Draft DPR V2 -...

Draft DPR - Pinjal Dam

March, 2012

Municipal Corporation of Brihan Mumbai

224604 ENI IWU 1 0


March, 2012

Municipal Corporation of Brihan Mumbai

Mott MacDonald, 703 ‘A’ Wing, Prism Tower, Mind Space, Goregaon West, Mumbai 400 062, Maharashtra, India T +91 (0)22 3981 0100 F +91 (0)22 3048 0600, W www.mottmac.com

The Deputy Chief Engineer (WSP) MCBM - 2nd Floor, Sri Chhatrapati Shivaji Maharaj Market Building, Palton Road Mumbai 400 001


Mott MacDonald, 703 ‘A’ Wing, Prism Tower, Mind Space, Goregaon West, Mumbai 400 062, Maharashtra, India

T +91 (0)22 3981 0100 F +91 (0)22 3048 0600, W www.mottmac.com

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0 19/03/2012 SM, SG, PP NR, RC DA

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Chapter Title Page

1 Introduction 1-1

1.1 General __________________________________________________________________________1-1 1.2 Present water supply _______________________________________________________________1-1 1.3 Recommendations of Dr.Chitale committee ______________________________________________1-2 1.4 Population and water demand projections _______________________________________________1-2 1.5 Objective_________________________________________________________________________1-4

2 Basin Characteristics 2-1

2.1 General __________________________________________________________________________2-1 2.2 Topography of the Region____________________________________________________________2-1 2.3 Geology__________________________________________________________________________2-1 2.4 Rainfall __________________________________________________________________________2-1 2.5 Temperature ______________________________________________________________________2-2 2.6 Relative Humidity __________________________________________________________________2-2 2.7 Wind Speed ______________________________________________________________________2-2

3 Preliminary Dam Studies 3-1

3.1 Introduction _______________________________________________________________________3-1 3.2 Alternative Dam Sites _______________________________________________________________3-1 3.2.1 Alternative 1 ______________________________________________________________________3-1 3.2.2 Alternative 2 ______________________________________________________________________3-1 3.2.3 Alternative 3 ______________________________________________________________________3-2 3.2.4 Alternative 4 ______________________________________________________________________3-2 3.3 Location of the Dam ________________________________________________________________3-4

4 Hydrology 4-1

4.1 Precipitation ______________________________________________________________________4-1 4.2 Runoff ___________________________________________________________________________4-2 4.3 Evaporation_______________________________________________________________________4-3 4.4 Consistency Checks of Data__________________________________________________________4-4 4.5 Derivation of Missing Rainfall Data _____________________________________________________4-5 4.6 Yield Series Derivation: Rainfall-Runoff Analysis __________________________________________4-5 4.6.1 NWDA Report – Releases from Damanganga to Pinjal _____________________________________4-5 4.6.2 Water Resources Department, GoM____________________________________________________4-7 4.6.3 Present Yield Study ________________________________________________________________4-7 4.7 Flood Studies _____________________________________________________________________4-7 4.7.1 Irrigation Department, GoM___________________________________________________________4-7 4.7.2 Present Flood Study ________________________________________________________________4-8 4.7.3 Derivation of Unit Hydrograph_________________________________________________________4-9 4.7.4 Design Infiltration Loss and Design Base Flow____________________________________________4-9 4.7.5 Design Storm _____________________________________________________________________4-9 4.7.6 Convolution_______________________________________________________________________4-9 4.7.7 Conclusion ______________________________________________________________________4-10 4.8 Sedimentation Study_______________________________________________________________4-10

Content

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4.8.1 Dead Storage Capacity_____________________________________________________________4-10 4.8.2 Trap Efficiency ___________________________________________________________________4-10 4.8.3 Sediment Rate ___________________________________________________________________4-10 4.8.4 Total Sediment Volume_____________________________________________________________4-11 4.8.5 Sediment Distribution ______________________________________________________________4-11 4.8.5.1 Empirical Area Reduction Method_____________________________________________________4-11 4.8.5.2 Moody’s Method __________________________________________________________________4-12

5 Storage Planning 5-1

5.1 Demand-Supply ___________________________________________________________________5-1 5.2 Reservoir Simulation Studies _________________________________________________________5-1 5.2.1 Inflows___________________________________________________________________________5-2 5.2.2 Outflows _________________________________________________________________________5-2 5.2.2.1 Dedicated Supply __________________________________________________________________5-2 5.2.2.2 Losses During Water Supply__________________________________________________________5-2 5.2.2.3 Environmental Flows________________________________________________________________5-2 5.2.2.4 Seepage _________________________________________________________________________5-2 5.2.2.5 Evaporation_______________________________________________________________________5-2 5.2.3 Storage-Elevation & Area-Elevation Curves ______________________________________________5-3 5.2.4 Sedimentation_____________________________________________________________________5-3 5.2.5 Reservoir Simulation________________________________________________________________5-3 5.2.6 Impact of Assuming Initial Reservoir Storage on the Simulation_______________________________5-4 5.3 Reservoir Storage__________________________________________________________________5-5 5.4 Intake Invert Level__________________________________________________________________5-5 5.4.1 Pinjal-Gundovili Link ________________________________________________________________5-5 5.4.2 Availability of Water for Alternate Uses__________________________________________________5-6 5.4.3 Potential Utilisation of Buffer Storage ___________________________________________________5-6 5.4.4 Abstract of Reservoir Simulation_______________________________________________________5-6 5.5 Hydropower Potential _______________________________________________________________5-7 5.5.1 Demand of Electricity in India _________________________________________________________5-7 5.5.2 Power and Energy Studies ___________________________________________________________5-8 5.5.3 Head for Power Generation __________________________________________________________5-8 5.5.4 Head Loss Calculation ______________________________________________________________5-9 5.5.5 Installed capacity __________________________________________________________________5-9 5.5.6 Size of Generating Units ____________________________________________________________5-10 5.5.7 Annual Energy Generation __________________________________________________________5-10

6 Dam Studies 6-1

6.1 Geotechnical Investigation ___________________________________________________________6-1 6.1.1 Subsurface Soil Profile ______________________________________________________________6-1 6.1.2 Bed Rock ________________________________________________________________________6-1 6.2 Type of Dam ______________________________________________________________________6-2 6.2.1 Earthen Dam (Homogeneous or Zoned)_________________________________________________6-2 6.2.2 Rock-fill Dam______________________________________________________________________6-3 6.2.3 Gravity Dam ______________________________________________________________________6-3 6.2.4 Arch Dam ________________________________________________________________________6-3 6.2.5 Selection of Type of Dam ____________________________________________________________6-4 6.3 General Layout of the Dam___________________________________________________________6-4 6.3.1 Control Levels of the Project__________________________________________________________6-4 6.3.1.1 Free Board _______________________________________________________________________6-4 6.3.1.2 Control Levels_____________________________________________________________________6-4 6.4 Diversion Works ___________________________________________________________________6-5 6.4.1 Coffer Dam _______________________________________________________________________6-5

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6.4.2 Diversion Tunnel___________________________________________________________________6-5 6.5 Dam & its Appurtenances ____________________________________________________________6-5 6.5.1 Foundation _______________________________________________________________________6-5 6.5.2 Non-Overflow Section_______________________________________________________________6-6 6.5.2.1 Stability Analysis___________________________________________________________________6-6 6.5.3 Overflow Section___________________________________________________________________6-8 6.5.3.1 Location of the Spillway _____________________________________________________________6-8 6.5.3.2 Design of Ogee Spillway_____________________________________________________________6-9 6.5.3.3 Energy Dissipation Arrangements______________________________________________________6-9 6.5.3.4 Spillway Gates ____________________________________________________________________6-9 6.5.4 Construction Sluice________________________________________________________________6-10 6.5.5 Training Walls ____________________________________________________________________6-11 6.5.6 Galleries ________________________________________________________________________6-11 6.5.7 Grouting & Drainage _______________________________________________________________6-11 6.5.8 Contraction Joints _________________________________________________________________6-12 6.5.9 Instrumentation ___________________________________________________________________6-12 6.5.9.1 Obligatory Measurements___________________________________________________________6-12 6.5.9.2 Optional Measurements ____________________________________________________________6-12 6.5.10 Lighting, Ventilation and Other Facilities Inside the Dam ___________________________________6-13 6.5.11 Hydropower Works ________________________________________________________________6-13 6.5.12 Bypass Arrangement ______________________________________________________________6-13 6.5.13 Infrastructural Works_______________________________________________________________6-13 6.5.13.1 Access Road and Internal Roads _____________________________________________________6-13 6.5.13.2 Diversion Road ___________________________________________________________________6-13 6.5.13.3 Housing Colony___________________________________________________________________6-14 6.5.13.4 Electrical Power Supply ____________________________________________________________6-14 6.6 Salient Features __________________________________________________________________6-14

7 Environmental & Social Issues 7-1

7.1 Baseline Conditions ________________________________________________________________7-1 7.2 Environmental Conditions ____________________________________________________________7-2 7.2.1 Pre-Construction Phase _____________________________________________________________7-2 7.2.2 Construction Phase_________________________________________________________________7-3 7.2.3 Operational Phase _________________________________________________________________7-3 7.2.4 Environmental Monitoring Plan ________________________________________________________7-4 7.2.5 Environmental Management Plan______________________________________________________7-8 7.2.5.1 Pre-Construction Phase _____________________________________________________________7-8 7.2.5.2 Construction Phase_________________________________________________________________7-8 7.2.5.3 Operational Phase _________________________________________________________________7-9 7.3 Social Conditions _________________________________________________________________7-10 7.4 Cost Estimation___________________________________________________________________7-11

8 Cost Estimates 8-1

8.1 Civil Works _______________________________________________________________________8-1 8.1.1 I - Works _________________________________________________________________________8-1 8.1.1.1 A—Preliminary Works_______________________________________________________________8-1 8.1.1.2 B—Lands ________________________________________________________________________8-1 8.1.1.3 C—Works ________________________________________________________________________8-1 8.1.1.4 K—Buildings ______________________________________________________________________8-1 8.1.1.5 M—Plantation _____________________________________________________________________8-2 8.1.1.6 O—Miscellaneous__________________________________________________________________8-2 8.1.1.7 P—Maintenance ___________________________________________________________________8-2 8.1.1.8 Q—Special Tools and Plant (Vehicles) __________________________________________________8-2

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8.1.1.9 R—Communications ________________________________________________________________8-2 8.1.1.10 X—Environment and Ecology _________________________________________________________8-2 8.1.1.11 Y—Losses on Stock ________________________________________________________________8-2 8.1.2 II - Establishment __________________________________________________________________8-2 8.1.3 III - Tools and Plant_________________________________________________________________8-2 8.1.4 V - Receipt and Recoveries on Capital Account ___________________________________________8-3 8.1.5 Indirect charges - Audit and accounts___________________________________________________8-3 8.2 Estimated Cost of the Project _________________________________________________________8-3

Appendices I

Appendix A. Data _____________________________________________________________________________ II A.1. Observed Monthly Rainfall ____________________________________________________________ II A.2. Observed Monthly & Annual Runoff at Andhari G&D Site_____________________________________ II A.3. Consistency Checks of Data___________________________________________________________ II A.3.1. Rainfall ___________________________________________________________________________ II A.3.2. Runoff ____________________________________________________________________________ II A.4. Pan Evaporation Depths ______________________________________________________________ II A.5. PMP Data (IMD) ____________________________________________________________________ II A.6. Silting of Reservoirs in India ___________________________________________________________ II A.7. Geotechnical Engineering Report _______________________________________________________ II Appendix B. Design____________________________________________________________________________III B.1. Derivation of Missing Rainfall Data ______________________________________________________III B.2. Weighted Monsoon Rainfall ___________________________________________________________III B.3. Rainfall-Runoff Model ________________________________________________________________III B.4. Yield Series & Dependable Yield _______________________________________________________III B.4.1. Andhari G&D Site___________________________________________________________________III B.4.2. Pinjal Dam Site _____________________________________________________________________III B.5. Synthetic Unit Hydrograph ____________________________________________________________III B.6. Design Flood_______________________________________________________________________III B.6.1. Temporal Distribution of Rainfall________________________________________________________III B.6.2. Design Storm (IMD) _________________________________________________________________III B.6.3. Design Flood (IMD)__________________________________________________________________III B.6.4. Design Storm (CWC) ________________________________________________________________III B.6.5. Design Flood (CWC)_________________________________________________________________III B.6.6. CWC Recommendations______________________________________________________________III B.7. Sedimentation Analysis_______________________________________________________________III B.7.1. Trap Efficiency _____________________________________________________________________III B.7.2. Sediment Distribution at 17.9 Ha-m/100sq.km/year for 100 years ______________________________III B.7.3. Sediment Distribution at 17.9 Ha-m/100sq.km/year for 50 years _______________________________III B.7.4. Sediment Distribution at 3.57 Ha-m/100sq.km/year for 100 years ______________________________III B.7.5. Sediment Distribution at 3.57 Ha-m/100sq.km/year for 50 years _______________________________III B.8. Monthly Inflow Series for Reservoir Simulation_____________________________________________III B.9. Reservoir Simulation Studies __________________________________________________________III B.10. Free Board ________________________________________________________________________III B.11. Head Loss for Hydropower Generation__________________________________________________ IV B.12. Hydropower Generation _____________________________________________________________ IV B.13. Diversion Tunnel___________________________________________________________________ IV B.14. Design of Ogee Spillway and Energy Dissipation Arrangements ______________________________ IV B.15. Stability Analysis of Overflow Section___________________________________________________ IV B.16. Stability Analysis of Non-Overflow Section – Main Gorge____________________________________ IV B.17. Stability Analysis of Non-Overflow Section – Shallow Gorge _________________________________ IV B.18. Summary of Stability Analysis_________________________________________________________ IV Appendix C. Cost Estimates _____________________________________________________________________ V

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C.1. Rate Analysis: Unit Rates _____________________________________________________________ V C.2. Cost Estimates _____________________________________________________________________ V C.2.1. Civil Works ________________________________________________________________________ V C.2.2. Hydroelectric Power Plant_____________________________________________________________ V C.2.3. Abstract of Project Cost ______________________________________________________________ V Appendix D. Drawings_________________________________________________________________________ VI D.1. MMD-224604-C-DR-PIN-XX-0001 INDEX MAP OF PINJAL DAM _____________________________ VI D.2. MMD-224604-C-DR-PIN-XX-0002 ALTERNATIVE LOCATIONS OF PINJAL DAM AND

SUBMERGENCE __________________________________________________________________ VI D.3. MMD-224604-C-DR-PIN-XX-0003 LAND USE PATTERN AT THE LOCATION OF PINJAL DAM ____ VI D.4. MMD-224604-C-DR-PIN-XX-0004 THIESSEN POLYGON NETWORK SHOWING RAIN GAUGES &

GAUGE DISCHARGE STATIONS FOR PINJAL CATCHMENT_______________________________ VI D.5. MMD-224604-C-DR-PIN-XX-0005 SURVEYED CROSS SECTION WITH BORE HOLE DETAILS

FOR PINJAL DAM LOCATION________________________________________________________ VI D.6. MMD-224604-C-DR-PIN-XX-0006 AREA CAPACITY CURVE________________________________ VI D.7. MMD-224604-C-DR-PIN-XX-0007 GENERAL LAYOUT OF PINJAL DAM AND APPURTENANT

WORKS _________________________________________________________________________ VI D.8. MMD-224604-C-DR-PIN-XX-0008 PLAN AND ELEVATION OF PINJAL RIVER SHOWING

OVERFLOW AND NON OVERFLOW DETAILS___________________________________________ VI D.9. MMD-224604-C-DR-PIN-XX-0009 CROSS-SECTION OF OVERFLOW (OGEE SPILLWAY)

SECTION AT CH. 595.00 M __________________________________________________________ VI D.10. MMD-224604-C-DR-PIN-XX-0010 CROSS-SECTION OF NON-OVERFLOW SECTION AT CH.

432.00 M_________________________________________________________________________ VI D.11. MMD-224604-C-DR-PIN-XX-0011 CROSS-SECTION OF NON-OVERFLOW SECTION AT CH.

1800.00 M IN SMALL GORGE ________________________________________________________ VI D.12. MMD-224604-C-DR-PIN-XX-0012 CROSS-SECTION OF NON-OVERFLOW SECTION WITH

PENSTOCK ARRANGEMENT FOR POWERHOUSE AT CH. 255.00 M ________________________ VI D.13. MMD-224604-C-DR-PIN-XX-0013 PLAN AND CROSS-SECTION OF POWERHOUSE ____________ VI

Tables Table 1.1: Present Demand___________________________________________________________________1-1 Table 1.2: Present Available Water _____________________________________________________________1-1 Table 1.3: Available Source___________________________________________________________________1-2 Table 1.4: Population Projection by Arithmetic Average Method _______________________________________1-3 Table 1.5: Water Demand projections for the year 2021 and 2041 _____________________________________1-3 Table 3.1: Comparative Statement of Alternative Sites ______________________________________________3-3 Table 4.1: Raingauge Stations_________________________________________________________________4-1 Table 4.2: Statistics of Rainfall Series ___________________________________________________________4-2 Table 4.3: Details of G&D Site_________________________________________________________________4-2 Table 4.4: Statistics of Observed Runoff Series ___________________________________________________4-2 Table 4.5: Results of Sedimentation Analysis ____________________________________________________4-12 Table 5.1: Buffer Storage Scenarios ____________________________________________________________5-6 Table 5.2: Input to Abstract of Reservoir Simulation ________________________________________________5-6 Table 5.3: Abstract of Reservoir Simulation_______________________________________________________5-7 Table 5.4: Growth of Hydropower Capacity _______________________________________________________5-7 Table 5.5: 90% Dependable Flows for Power Generation ____________________________________________5-8 Table 5.6: Limits of Hydropower Generation ______________________________________________________5-9 Table 6.1: Subsurface Soil Properties ___________________________________________________________6-1 Table 6.2: Rock Properties ___________________________________________________________________6-2 Table 6.3: Uniaxial Compressive Strength of Rock Specimens________________________________________6-2 Table 6.4: Control levels of Pinjal Dam __________________________________________________________6-4 Table 6.5: Foundation Depths of the Dam ________________________________________________________6-6

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Table 6.6: Parameters considered in design of Pinjal Dam __________________________________________6-7 Table 6.7: Spillway Gate Dimensions __________________________________________________________6-10 Table 6.8: Salient Features __________________________________________________________________6-15 Table 7.1: Environmental Impacts ______________________________________________________________7-4 Table 7.2: CPCB Pollutant Concentration Limits ___________________________________________________7-5 Table 7.3: Classification of Water ______________________________________________________________7-5 Table 7.4: Environmental Parameters to be Monitored ______________________________________________7-6 Table 7.5: Environmental Management Plan______________________________________________________7-9 Table 7.6: Social Impacts and Management _____________________________________________________7-11 Table 7.7: Social Impact Mitigation and Monitoring Plans ___________________________________________7-11

Figures

Figure 4.1: Seasonal Runoff Variation ___________________________________________________________4-3 Figure 5.1: Installation Capacity for Hydropower __________________________________________________5-10

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1.1 General

Mumbai, the financial hub of India, is one of the rapidly populating cities, with a population of around

14.5 million. While majority of the population resides at the suburbs of the city, considering the

convenience to commute and other factors, the city has grown beyond its limits in accommodating the

people. Out of many infrastructural facilities provided by the city’s officials, assured water supply is

one of the major factors that contribute to large migration of people to Mumbai and meeting the

demand of water is one mammoth task as such. The Municipal Corporation of Greater Mumbai

(MCGM) has taken up initiatives to continuously supply water to the huge population and keep pace

with development as well. This resulted in searching new sources of water supply with conservation

measures as the main goal, thereafter fulfilling the growing demand of water supply for Mumbai.

1.2 Present water supply

The present estimated population of Mumbai is about 14.5Million. About 40% of this total population

resides in slum and remaining 60% in planned development. Slum population is eligible for availing

the water supply of 45 lpcd where as water supply to population in planned development is 135 lpcd.

Due to ongoing slum rehabilitation programme, cluster developments in the city, redevelopment of old

houses and development of land due to closure of textile mills with Floor Space Index(FSI) incentive,

increase in water demand is at very rapid rate. The national norm as per CPHEEO manual is 150lpcd.

The present demand with existing residential consumption pattern, industrial and commercial

requirement of about 500 MLD available supplies is tabulated below:

Table 1.1: Present Demand

Description Population (million) Supply Norms

(lpcd) Total Demand in

MLD

Population 14.5

Slum 40% 5.8 100 580

Planned Development 60% 8.7 200 1740

Industrial and commercial Demand 500

Leakages in distribution system at 30% 1208

Losses at WTP @ 0.25% 10

Transmission losses @2% 80

Add Enroute supply 120

Total

4238

Say 4240

Table 1.2: Present Available Water

Source Yield at source in MLD

Tulsi 18

Vehar 90

Tansa 410 + 90 Enroute

1 Introduction

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Source Yield at source in MLD

Modak sagar 455

upper vaitarna 635

Bhatsa I+II+III+IIIA+IIIB 1820

Total

3518

Say 3520

Above tables indicates a deficit of about 17% in available water supply against the demand and overall

satisfaction level of about 83%. Present water supply is intermittent supply hours ranging from 2hrs to

more than 12hrs depending upon the location of the water supply zone, drawal facility and the water

distribution network.

1.3 Recommendations of Dr.Chitale committee

The expert committee was appointed by Govt of Maharashtra in the year 1993, under the

chairmanship of Dr. Chitale (Ex-Secretary, Irrigation Dept) for advice on the long term planning for

augmentation of water supply to Mumbai. The committee recommended water supply norms for the

city at 240 lpcd considering the climate in Mumbai city, habits, and requirements for good health and

to prevail good environmental conditions. Based on the surveys carried by the committee, considering

the subtropical climate and modern gadgets, the planned development requirement is worked out as

240lpcd and that of slum at 150lpcd, considering the continuous water supply system. The committee

also recommended development of following sources in phases.

Table 1.3: Available Source

Sr. No. Source Basin Yield [MLD]

1 Middle Vaitarna Vaitarna 455

2 Gargai Vaitarna 455

3 Pinjal Vaitarna 865

The GoM has accepted Dr. Chitale Committee recommendations and approved the above mentioned

sources. MCGM has therefore taken up the Middle Vaitarna Project as an immediate additional source

of water supply. Simultaneously feasibility studies of Gargai and Pinjal Projects are under process.

1.4 Population and water demand projections

Mumbai City is the Financial Capital of India and has recorded highest rate of influx of migrants from

all parts of the country for past many years and will continue to attract people from all parts of India in

future too. The city has good infrastructure to cater the needs of the residents. Population growth

pattern of Mumbai is continuously rising and according to report of M/s Lee Associates, the

consultants appointed by Mumbai Metropolitan Region Development Authority (MMRDA) in the year

2007 for infrastructural development of Mumbai Metropolitan region (MMR), the population growth

pattern of past will continue till the year 2031. Population projection from the year 2031 to 2041 is

projected based on arithmetic average method which is adopted for old cities and small towns.

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Table 1.4: Population Projection by Arithmetic Average Method

Years Population

(millions)

Increase in Population

(millions)

Average increase in Population (1951-2031)

(millions)

Projected population till 2041

(millions)

1951 3.00 0.00

1961 4.20 1.20

1971 6.00 1.80

1981 8.30 2.30

1991 9.90 1.60

2001 11.98 2.08

2011 14.52 2.54

2021 17.15 2.63

2031 19.39 2.24

2041 21.21 1.82

1.82 21.21

The population growth till the year 2031 is linear projection of census population available form the

year 1951 to 2001. Further projection is done by arithmetic average of increase from the year 1951 to

2031 i.e. 1.82 million per decade. The population for the year 2041 with the above average, adopted

for old cities works out to 21.21Milllion.

The water demand projections for the year 2041 are based on following assumptions made by

Dr Chitale committee.

� Population in slums are supplied at the rate of 150 lpcd (24X7 scenarios).

� The consumers in the planned developments will continue to draw water at the rate of 240 lpcd.

Table 1.5: Water Demand projections for the year 2021 and 2041

Description Supply Norms in

lpcd Total demand in MLD (2021) Total Demand in MLD (2041)

Total population in Million 17.15(2021) 21.21(2041)

Slum (30%):

5.145 million(2021)

6.363 million(2041) 150 772 955

Planned Development (70%)

12.005 Millions (2021) 14.847 million (2041) 240 2401 3564

Industrial & Commercial Demand 550 550

Leakages in Distribution System @ 20% 930 1268

loses in at water treatment plant @ 0.25% 12 16

loses in transit & transmission @ 2% 94 128

Add enroute supply 150 200

Total 4909 6680

Thus at source the demand will be about 4909 MLD in the year 2021 and 6680 MLD in the year 2041.

Present available quantity at source is 3520 MLD against water demand of 4240MLD. The

augmentation will not only improve the satisfaction level but also facilitate continuous water supply and

to take the effective leak control measures. Demand and supply gaps are as follows:

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Year Total Demand, MLD Total Supply Existing, MLD

Demand / Supply Gap, MLD

2011 3926 3668 258

2021 4909 4168 741

2041 6680 4168 2512

1.5 Objective

The objective of this report is to study feasibility of Pinjal dam and prepare detailed project report

including detailed costs suitable for budgeting and take up construction works along with detailed

construction designs.

The report covers various aspects related to developing a storage reservoir on the Pinjal River, with

the aim of delivering a minimum yield of 865 MLD with 100% reliability. These include – investigation

details, designs, environmental and social studies and cost estimates.

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2.1 General

Origination of Pinjal is on the rocky slopes of Utwad Dongar(Hill), north of ridge separating the Upper

Vaitarna lake, at an elevation above 980 m formed by two streams in its initial course, with Utwad dongar

as the major one other branch arising at Shirghat towards south of the ridge at a lower elevation of 600 m

datum. Utwad dongar confluences with Kalakapri Nadi (River), taking a southward course.

A well defined Pinjal River emerges after its confluence with Devbandh Nadi, taking a South-Westerly

course, flowing south of the North Jawhar Nadi, until its confluence with Gargai River. Pinjal continues the

same course and joins Vaitarna near the villages of Alman/ Pingepada situated about 35 km downstream of

Modak Sagar dam that is built over Vaitarna River. The ground elevation at its confluence with Vaitarna

River is about 30 m. The length and catchment area of the Pinjal River up to its confluence with Vaitarna is

85 km and 654.3 square kilometers (sq.km) respectively.

The levels mentioned in the report are with respect to Mean Sea Level (MSL). MSL is 24.46m below the

Town Hall Datum( THD). Thus, for arriving at THD levels, Mean Sea Levels mentioned in this report should

be added with 24.46.

2.2 Topography of the Region

The topographical information pertaining to the Pinjal basin is available with Survey of India. This is covered

in toposheets (of scale 1:50,000) numbered 47E/1 and 47E/2.

The Sahyadri Range, which runs North to South, forms an unbroken boundary and has number of off-

shoots besides many spurs, isolated peaks, such as Kalsubai Harischandra Ghat and Matheran. The

general topography of the region is very undulating and crossed by various ranges, which are generally

lower in height as one travels West towards Arabian Sea from the main continental divide. The river has

steep slopes and is deep due to flow through narrow valleys; most of the flow takes place on rock beds in

its initial reaches, while the valleys open wide in its lower reaches. Lower reaches of the river mainly consist

of alluvial plains. River flows are interrupted by a large number of dykes of varying thickness. The climatic

condition in this region is tropical, very humid and warm. The proposed dam site is encountered by nine

lava flows of Deccan basalt, varying in thickness from 7 to 25 m.

2.3 Geology

The area is extensively covered by 766 m thick pile of basaltic lava flows of the Deccan Traps that occurred

during Upper Cretaceous to Palaeogene age. The basalt flows are typically quartz and hypersthenes,

normative with minor amounts of olivine theolites. The lava flows are classified under Sahyadri group which

divisible into eight formations. The oldest Salher formations are represented by a megacryst flow

constituting the top of this formation. This is overlain by Lower Ratangarh formation, comprising of mainly

compound pahoehoe flows exposed in the area.

2.4 Rainfall

Pinjal river basin receives most of its rainfall from the South-West monsoon during June to September.

Around 95% of the annual rainfall occurs during monsoon season and rest of the rainfall is mainly due to

orographic and convectional rains. July is the wettest month, with a rainfall of about 40% of the annual

2 Basin Characteristics

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rainfall. Annual maximum and minimum recorded rainfalls are 4,556 mm and 1,392 mm, respectively. The

average annual rainfall is 2,429 mm.

2.5 Temperature

The maximum average daily temperature is 32.9°C during April month. The minimum average daily

temperature is 16.8°C during January month.

2.6 Relative Humidity

Relative humidity is high during monsoon and low during spring, varying from 32% during March to 89%

during August.

2.7 Wind Speed

The basin falls in wind zone-II as per Indian Standards (IS 875) with a normal wind speed of 39.0 m/s.

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3.1 Introduction

For the stated purpose of building a dam on the Pinjal River, to meet the future demand of Mumbai city, a

suitable dam site must first be identified. A site selected for a storage reservoir needs to facilitate required

storage reliably and to safely take up the construction without causing great environmental setbacks and

involving minimal relocation and rehabilitation of the people affected by the project. Important rules in

selecting a dam site include the following:

� The site must be adequate enough to support the dam and its appurtenant structures

� The area for a reservoir dam need to be in a straight and narrow river reach with sufficient area on its

upstream to hold the planned storage

� The foundation of the dam should be relatively free of major faults and shears

3.2 Alternative Dam Sites

In line with the norms stated above in choosing a dam site, four alternative locations have been identified,

studied and presented at pre-feasibility stage, for proposing a dam over Pinjal River. Details of these

locations are shown in Drawing No. MMD-224604-C-DR-PIN-XX-0002; each of them is described in the

following sub-sections:

3.2.1 Alternative 1

It was proposed to locate the dam to store a catchment driven yield of about 185 million cubic meters

(MCM) at 75 % reliability covering the drainage of about 121 square kilometers (sq.km). This location is just

downstream of the confluence of two of Pinjal’s tributaries, Kalakapri Nadi and Devbandh Nadi. Pinjal River

opens wide in this vicinity, thus increasing the length between stable banks. The river bed level at this

reach is about MSL 200.00 m. This location may be useful to serve as upstream balancing reservoir than a

feeder because, standing alone, it cannot completely serve the supple objective of 865 million litres per day

(MLD). The yield at this location is less than 50% of the contemplated river yield, which necessitates for one

more storage reservoir downstream of this location to act as a feeder. This increases the cost per cubic

metre storage of water created, as well as doubles the environmental impacts due to the project.

The submergence area of the proposed dam at this site, for an FRL of 260.0 m, is 14.7 sq.km, with

moderate forest cover. This requires clearing of forests while creating planned storage, causing loss of

valuable species of existing flora and fauna. Deforestation would also result in erosion of soil, leading to

sedimentation problems. This alternative also requires displacement of the inhabitants of Pathardi,

Thakurwadi, Bhospada, Botashimal, Bhueiteki and Bhurreki villages.

As no roads are close by, approach to the dam site requires laying new roads and communication systems.

Thus, the cost per unit storage of water created through this Alternative is large, hence not a preferred

alternative.

3.2.2 Alternative 2

Another alternative location of the dam, further downstream compared to Alternative 1, is identified. It

covers about 174 sq.km of drainage area. The river bed level at this location is 140 m. Increase in storage

capacity is not appreciable (about 250 MCM) in comparison to the increase in height of the dam and cost.

3 Preliminary Dam Studies

3-2 224604/ENI/IWU/1/0


The area of submergence at this location is 11.0 sq.km with villages getting displaced being Barpawadi

Bahgatwadi and Akhada. The surrounding villages, namely, Hedvali, Bhopatgarh, Vadoli and Manchepada

are likely to get affected due to submergence connecting roads

The meandering course of the river prior to and after the proposed dam location is also not favourable to

take up the storage dam at this location. Hence, the same is not considered as a feasible option.

3.2.3 Alternative 3

This location is on upstream of the confluence with Gargai River, near Khidse village, Jawhar taluka of

Thane District in Maharashtra state. Drainage area up to the proposed alternative is 316 sq.km. The

corresponding annual catchment yield is 421.6 MCM and 512.3 MCM, at 95% and 75% dependability,

respectively. The yield of the river at this location is sufficient to meet the annual demand of water supply.

At full reservoir level (FRL) of 145.0 m, its submergence area upstream of the dam location is 20.0 sq.km.

This location also satisfies the following:

� Shape of the river valley at this site is nearly narrow which minimizes the dam length, thus reducing the

project cost per unit storage

� Dam site is open to a large drainage area on upstream to tap the desired inflows to fill the storage facility

� Neither the dam nor the area of submergence created by it falls within the reserved wildlife region

� Rim of the proposed storage is water-tight and stable

� Submergence due to water-spread is minimum

� Minimum cost of connectivity like roads, housing colonies, etc. due to the presence of existing road

networks towards both banks of the river

� Alignment of dam is across a straight reach of channel

� Avoids river-meandering locations immediately on upstream and downstream of proposed dam site

3.2.4 Alternative 4

One of the major setbacks in locating the dam after the confluence of Gargai River with Pinjal River is that a

part of submergence falls within the Tansa Wildlife Sanctuary, which plays host to an extensive variety of

flora and fauna. Nearly 50 types of animals and approximately 200 species of birds can be found in this

region.

Catchment area up to this alternative dam site is 368 sq.km, the river bed level being at 60 m. At this

location, the area of submergence is 22.9 sq.km for an FRL of 100.0 m. The yield of the river at this

location, as compared to that of Alternative 3, would be about 20% higher. However, as the Pinjal River

beyond its confluence with Gargai River opens wide, the length of the dam between stable banks increases

(about 8,500 m), in effect increasing the cost per unit storage substantially. Hence, this alternative is

discarded.

A brief of comparison between the alternatives considered for locating the dam site on Pinjal River is given

in Table 3.1.

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Table 3.1: Comparative Statement of Alternative Sites

Description Alternative 1 Alternative 2 Alternative 3 Alternative 4

Drainage Area (sq.km) 121.0 174.0 316.0 368.0

River Bed Level (m) 200.0 140.0 75.0 60.0

FRL (m) 260.0 200.0 145.0 100.0

Height of Dam above RBL (m) 60.0 60.0 70.0 40.0

Submergence Area (sq.km) 14.7 11.0 20.0 22.9

Length of proposed dam (m) 2400.0 1760.0 750.0 8580.0

95% Dependable Annual Yield (MCM) 161.0 232.0 421.6 491.0

75% Dependable Annual Yield (MCM) 185.0 250.0 512.3 596.6

Storage Requirement

Requires

another reservoir

to fulfil the

required demand

Requires another

reservoir to fulfil the

required demand

Sufficient storage can be created to meet

the downstream demand

Sufficient storage capacity can be

created, but the submergence area and

the length of the dam is large, which in

turn increases the project cost

Design Flood (cumecs) 2060.0 2963.5 5382.0 6267.7

Villages that get affected

Pathardi,

Thakurwadi,

Bhospada,

Botashimal,

Bhueiteki and

Bhurreki

Barpawadi Bahgatwadi

and Akhada

Hedvali, Bhopatgarh,

Vadoli and

Manchepada are likely

to get affected due to

submergence

connecting roads.

Khidse, Ujjani, Vire, Manmohai,

Manmowadi, Ene, Vadoli, Hedvali, Akhada,

Bhagatwadi, Barpachiwadi. Ongorichapada,

Dhaknichapada, Kondichapada,

Dakachapada, Vadachapada,

Kukaronapada, Ujjanipada and Bhatipada

Andhari, Dhabon, Vanganpada,

Chinchpada, Bhoirpada, etc.

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3.3 Location of the Dam

Alternative 3 is recommended for constructing a dam across Pinjal River as it satisfies the criteria

mentioned in Section 3.2.3. Coordinates of the dam site are: (19°47’0’’ N, 73°13’0’’ E). Catchment area up

to proposed dam site is 316 sq.km. The exact dam location and alignment have been fixed, based on

economical and hydrological considerations, by referring to relevant toposheets. Bore-log studies have also

been carried out to check the consistency of the foundation rock (see Section 6.1). Bore-log details have

been shown in Drawing No. MMD-224604-C-DR-PIN-XX-0005. Land-use map of the region is shown in

Drawing No. MMD-224604-C-DR-PIN-XX-0003. Hydrological studies, storage planning, preliminary designs

of the dam and appurtenant works, potential generation of hydropower are carried out for the proposed

dam site at this location. These studies are detailed in the subsequent chapters.

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4.1 Precipitation

Precipitation data for Pinjal basin is obtained from the State Data Storage Centre (SDSC) of Maharashtra

Government located at Nasik. SDSC has repositories of all hydrological and meteorological data related to

major river basins in Maharashtra state under the Hydrology Project (I & II). Precipitation data is obtained

from the SDSC in the form of daily recorded depth in mm of self-recording gauges (SRG’s).

Areal average rainfall, i.e. mean rainfall over a given area, is used to calculate runoff of a river. However,

areal average rainfall over a catchment cannot be measured at all times. Therefore, a finite number of rain

gauges are used to estimate an average value of rainfall over the entire catchment. This averaging can be

done using several methods, such as arithmetic-mean method, isohyetal method, Thiessen polygon

method, reciprocal-distance-squared method, etc. While studying Pinjal catchment, the Thiessen polygon

method is used to calculate the areal average rainfall.

The Thiessen polygon method of calculating areal average rainfall assumes that at any point in the

catchment, the rainfall is the same as that at the nearest gauge. So, the rainfall depth recorded at a given

gauge is applicable to a distance halfway to the next gauging station in any direction. Thus, portions of the

catchment area concerned are assigned to a raingauge. The rainfall over the entire catchment area is

estimated as the weighted average of rainfall at individual gauges, weighted using fractions of area

assigned to respective gauges.

∑=

=

J

j

jj PAA

P1

1 … (4.1)

where J is the total number of raingauges; jA is the area within the watershed assigned to jth gauge; jP is

the rainfall recorded at the jth gauge; and, the catchment area, ∑

=

=J

j jAA1

. There are J = four (4)

raingauge stations in and around the Pinjal catchment, the details of which are given in Table 4.1.

Table 4.1: Raingauge Stations

S.No. RG Station Period of data availability Number

of years Remarks

1 Suryamal 1981 to 2007 27 years Missing year - 2008

2 Mokhada 1901 to 2008 108 years

3 Jawhar 1955 to 2008 54 years

4 Khodala 1976 to 2007 32 years Missing year - 2008

Locations of these stations are shown in the Thiessen Polygon Map, attached as Drawing No. MMD-

224604-C-DR-PIN-XX-0004. Daily values of precipitation are available for all days of monsoon months viz.

from June to October, and up to November in some years. Daily values at Mokhada are available from

1901 to 2008 and is the longest record for 108 years, while that at Suryamal is for 27 years only (1981 to

2007) and is the shortest record. The maximum and minimum values of annual rainfall were recorded at

Khodala (4,556 mm during 1976-77) and at Mokhada (1,392 mm during 1918-19), respectively. Monthly

rainfall values (Appendix A.1) have been processed from daily data. For each station, month-wise

statistical parameters, like means/ standard deviations and coefficients of variation (CV), have been

4 Hydrology

4-2 224604/ENI/IWU/1/0


calculated. The mean, standard deviation and coefficient of variation of rainfall for Pinjal catchment is given

below, in Table 4.2.

Table 4.2: Statistics of Rainfall Series

MONTH June July August September

Mean 459.74 1000.06 829.00 335.44

Standard Deviation 183.76 352.32 302.26 205.17

Coefficient of Variation 0.40 0.35 0.36 0.61

From the above table, it is evident that the variation in rainfall is more during the starting and ending months

of monsoon, i.e. June and September, respectively. The variation during other monsoon months is lesser,

although when seen absolutely, it is significantly large. This means that the resulting runoffs may also vary

significantly, which impacts the design of Pinjal dam, both hydrologically as well as structurally. The

question of variability in runoff is probed further in the following section.

4.2 Runoff

A self-recording gauge located near village Andhari, Jawhar taluka of Thane district of Maharashtra, had

been recording Pinjal’s flows since 1976. Flow data available for the studies comprises of daily average

values recorded in cubic metres per second (cumecs or m3/s) at the gauge discharge station. Details of

data availability are as given in Table 4.3. The data covers the monsoon season fully, extending beyond

October in certain years. Observed data suggests that recessed low flows prevail in Pinjal till December.

The daily flow values have been processed to generate monthly and annual flows. Compiled monthly and

annual flows at Andhari gauge discharge station are shown in Appendix A.2.

Table 4.3: Details of G&D Site

Name of G&D Site Andhari

River/ Tributary Vaitarna/ Pinjal

Catchment Area (km2) 326.40 (say 327)

Period of availability of data 1975 to 2004 (30 years)

Annual mean flows of Pinjal at Andhari are calculated as 866 MCM and maximum flows occur in July

month. Seasonal variation of runoff based on the monthly averaged flows is presented in Figure 4.1.

Statistics of virgin flows of Pinjal River are summarised in Table 4.4.

Table 4.4: Statistics of Observed Runoff Series

River Annual

Mean

(MCM)

Standard

Deviation

(MCM)

Coefficient

of Variation

Skewness

Coefficient

Lag-1 Serial

Coefficient

Pinjal 865.5 336.9 0.39 0.88 0.28

Above table indicates that the variation in runoff series at Andhari G&D site is significant. A low value of lag-

1 serial coefficient highlights that the annual flows in Pinjal are independent. This means that the runoff

volume in Pinjal River in a given year is not dependent on that in the preceding year. Such independence of

data is useful when certain data points need to be either discarded or generated, due to inconsistencies in

observed runoff values or for extrapolation of the data set. The rainfall-runoff model, as described in

Section 4.6, uses lag-1 independence of runoff data in order to be developed.

4-3 224604/ENI/IWU/1/0


Figure 4.1: Seasonal Runoff Variation

0.00

50.00

100.00

150.00

200.00

250.00

300.00

350.00

June July August September October November December

Month

Avera

ge M

on

thly

Ru

no

ff (

Mcu

m)

4.3 Evaporation

Daily recorded data of pan evaporation at Suksale station (Vikramgarh taluka, Thane district) for the years

during 1994 to 2006 are considered for this study. Suksale is situated in a plain area at an elevation of 100

m (datum) outside the catchment boundary of Pinjal basin. 13 years of Suksale data have been processed

to generate mean monthly depths of evaporation, as presented in Appendix A.4. The annual mean

evaporation depth is 1,602 mm. The mean evaporation depth recorded for the month of August is 56 mm,

which is the lowest and that of May is 237 mm, the highest in a year. The observed values of pan

evaporation are multiplied by a Pan Factor to convert them to equivalent open-water evaporation values.

Following the practice of the Irrigation Department, pan factors to be applied to different seasons have been

assumed as below:

From 1st July to 14

th October = 0.7

From 15th October to 28

th February = 0.6

From 1st March to 30

th June = 0.8

On the basis of the above, an average pan factor over the whole year works out to 0.7. Monthly pan factors

are used to estimate the evaporation loss of water during reservoir simulation.

4-4 224604/ENI/IWU/1/0


4.4 Consistency Checks of Data

A time series is said to be consistent if all its values belong to the same statistical distribution. Inconsistent

data should not be used to predict the design parameters, since such data may indicate change in regime

of the concerned parameters, which needs to be accounted for while estimating them for design purposes.

A dataset may not be consistent due to various reasons. Some of them are (i) changes in the underlying

process or system, and (ii) changes in measuring the variables of the system, including defects in

equipment. In case of spatially variable measurements, such as rainfall, inconsistency resulting from the

former reason will be reflected in measurements taken at different locations. In such a case, the dataset

needs to be handled as it is, and no corrections need to be made to it. However, if it is the latter reason,

then, the inconsistency will be seen only in those measurements taken from that specific equipment where

changes have occurred.

Changes in working of raingauges can be checked and corrected, if necessary, through consistency checks

on data collected from them. Checking for inconsistency of a given dataset, which is one among many such

datasets collected, is done by double-mass curve technique. This method compares cumulative rainfall

measurements at a given raingauge station to the cumulative mean rainfall measurements at all the other

raingauge stations chosen to calculate the areal average rainfall over the catchment. It is important to note

that the accumulation of values is started from the latest record, backwards. A sudden change in the slope

of curve resulting from such comparison indicates a “changed” raingauge. This test is repeated on all the

raingauges of concern. In the event of finding changed equipment, the precipitation values beyond the

period of change of regime is corrected using the relation

a

c

xcxM

MPP = … (4.2)

where, cxP = corrected precipitation at any time period at station X

xP = original recorded precipitation at the same time period at station X

cM = corrected slope of the double-mass curve

aM = original slope of the double-mass curve

For datasets that are not prepared in conjunction with other datasets, consistency may be checked using

single-mass curve technique. For example, runoff of a river at a given point along its length may be

checked for consistency using this method. The cumulative values of runoff time series are plotted with

respect to time. Next, the plot is checked for changes in slope, which indicates a change in regime of the

variable under concern, runoff in our case, and hence, its consistency.

The following checks were performed to test the consistency of the data obtained from various sources.

They are:

1. Consistency based on Rainfall:

Data from all the four raingauge stations have been checked using double mass curve method, before

being used in the rainfall-runoff analysis. Details of consistency checks are attached as Appendix A.3.1. It

was observed that the data at all the stations is consistent.

2. Consistency based on Runoff:

Runoff data of Andhari G&D site has been checked for consistency using single mass curve method, before

being used for the rainfall-runoff analysis. These details also can be seen in Appendix A.3.2. Runoff during

4-5 224604/ENI/IWU/1/0


almost all the monsoon months has been found to be consistent, except during June. Data belonging to the

entire monsoon period has also been found to be consistent.

3. Consistency of Runoff by Runoff Factors:

The runoff data at Andhari G&D site, with a catchment area of 327 sq.km, has been verified by weighted

monsoon rainfall (WMR) for Pinjal catchment, using the Thiessen weights as discussed above. The

calculations are given in Appendix B.2. It is, thus, identified that the runoff data is not consistent in general,

with runoff values greater than rainfall over the basin for many years. The flow data of these years have

been discarded and same have been modified using rainfall-runoff modelling. However, before creating a

rainfall-runoff model, missing rainfall data were filled, the details of which are in the following section.

4.5 Derivation of Missing Rainfall Data

Periods of rainfall data availability at different stations identified for the study varies, and in some cases, the

data availability is only for a short duration. In the case of the raingauges chosen for this study, rainfall data

is available at almost all the stations from the year 1975—76 to 2008—09. Thus, this period has been

considered in the study. Missing data within this period, at different raingauge stations, have been

estimated using the normal ratio method, since the average monthly precipitation values at different

raingauge stations vary by more than 10%.

The normal ratio method proposes that a missing data point, at a given raingauge station and time period,

can be estimated as the weighted average of precipitation at other stations, where data pertaining to the

same time period is available. The weights used are the values of normal annual precipitation, i.e. 30-year

rainfall averages at the same duration as of that being estimated (a particular date, month, year, etc.). For

Pinjal studies, monthly precipitation values have been used. Thus,

+++=

m

mx

xN

P

N

P

N

P

M

NP ...

2

2

1

1 … (4.3)

where, xP , xN are the missing monthly precipitation and normal monthly precipitation, respectively, at a

raingauge station X; and mPPP ,...,, 21 & mNNN ,...,, 21 are the corresponding monthly precipitation and

normal monthly precipitation values at the neighbouring M stations 1, 2, … , M, respectively.

The details of gap-filling of missing data for the four (4) raingauges chosen for this study are presented in

Appendix B.1.

4.6 Yield Series Derivation: Rainfall-Runoff Analysis

4.6.1 NWDA Report – Releases from Damanganga to Pinjal

As per the Municipal Corporation of Greater Mumbai (MCGM), the projected water demand for Greater

Mumbai by 2021 AD is 1,789 MCM, equivalent to 4,900 Million litres per day (MLD). The present water

supply from different sources, viz., Vaitarna, Tansa, Bhatsa, Vehar and Tulsi rivers is 1,075 MCM (2,945

MLD) only. As such, there will be a shortage of 714 MCM (1,955 MLD) by 2021 AD. In order to cope up

with above requirement, it is proposed to divert surplus available water from Damanganga basin to Greater

Mumbai through Pinjal reservoir. Feasibility studies were carried out by National Water Development

Agency (NWDA) for “Damanganga-Pinjal Link Project”, which is a part of “Peninsular Rivers Component”

envisaging “Interlinking of West Flowing Rivers North of Mumbai and South of Tapi”. Damanganga-Pinjal

Link Project envisages transferring surplus water at the proposed Bhugad reservoir across Damanganga

River and Khargihill reservoir across Vagh River, a tributary of Damanganga River in Damanganga basin,

4-6 224604/ENI/IWU/1/0


for augmentation of water supply to Greater Mumbai, to meet its domestic and industrial water

requirements in the near future.

The following are some of the key lines of the project:

� The FRL of the Bhugad reservoir is fixed at 163.87 m based on detailed surveys and investigations. The

gross and live storage capacities of the reservoir are 426.39 MCM and 400.00 MCM, respectively.

� The total catchment area of Damanganga basin up to Bhugad dam site is 729 sq.km, of which 141

sq.km lies within the Gujarat state, while the remaining 588 sq.km lies within the Maharashtra state.

� 287 MCM of water at 100% dependability is proposed to be diverted from Bhugad reservoir to Khargihill

reservoir through Bhugad-Khargihill link tunnel (5.0 m diameter, 16.85 km long) during non-monsoon

period at supply rate of 1181 MLD. However, NWDA in a meeting held in Nov 2011 has informed MCBM

that the releases into Pinjal reservoir shall be on a continuous basis throughout the year.

� A 572.80 m long composite dam across river Vagh at Khargihill site near village Behadpada (Mokhada

taluka, Thane district, Maharashtra state) is proposed.

� The FRL of the Khargihill dam, fixed on the basis of detailed surveys and investigations, is 154.52 m.

The gross and live storage capacities have been fixed as 460.79 MCM and 420.50 MCM, respectively.

� The maximum height of the Khargihill dam would be 75.62 m. Catchment area up to this dam site is 710

sq.km, the whole of which lies in Maharashtra State

� The amount of divertible water at Khargihill dam, at 100% dependability, is 290 MCM during non-

monsoon period at supply rate of 1193 MLD.

� Thus, a combined release of 577 MCM (287 + 290 MCM) or 2374 MLD will be diverted through the

Khargihill-Pinjal link tunnel (5.25 m diameter, 25.7 km long) in to Pinjal reservoir, for downstream

demands, during non-monsoon periods.

The NWDA report also included the following details regarding the Pinjal dam:

� A 681 m long dam on Pinjal River near Khidse village (Jawhar taluka, Thane district)

� Its FRL has been fixed, on the basis of detailed surveys and investigations carried out by Government of

Maharashtra, as 141.00 m

� The gross and live storage capacities have been fixed as 413.57 MCM and 401.55 MCM, respectively

� Catchment area of the Pinjal sub-basin up to this dam site is 316 sq.km, the whole of which lies in the

Maharashtra state

� The divertible water to Mumbai city at Pinjal dam site at 75% dependability (as fixed by the Government

of Maharashtra) is 332 MCM (1,367 MLD).

� Thus, a combined release of 43.84 cumecs of water i.e. 3,741 MLD (= 2,374 MLD + 1,367 MLD) will be

diverted through Pinjal reservoir as envisaged by Government of Maharashtra.

4-7 224604/ENI/IWU/1/0


4.6.2 Water Resources Department, GoM

The Water Resources Department of the Government of Maharashtra had conducted a study on the Pinjal

River in the early 1970’s, in which a 71 m high masonry dam was proposed at almost the same location

(CA = 316.2 sq.km) as suggested by this report (CA = 316 sq.km). The dam proposed by the WRD,

however, was to irrigate 23,594 Ha of land in Thane district, Maharashtra. The 75% dependable yield at this

location was established as 444 MCM in this study.

4.6.3 Present Yield Study

Considering the above studies, however, the current yield, i.e. from the year 1976 to 2004 (30 years), at the

Andhari G&D site has been checked with WMR of catchment of Andhari. The results thus obtained had a

presence of outliers. Therefore, a rainfall-runoff model for the monsoon period (June—September) was

developed, the calculations of which are attached as Appendix B.3.

The steps followed in creating the rainfall-runoff model are as listed below:

1. Thiessen weights for all four (4) raingauge stations are determined

2. Annual WMR values, for a 30-year period (1975—2004), up to Andhari G&D site are calculated by

summing up weighted rainfall values for each monsoon month (June—September)

3. WMR values in mm for each year are compared to runoff values measured at Andhari G&D site in

mm for the same year

4. Runoff data of those years, in which the runoff depths are comparable (99%) to or greater than the

corresponding rainfall depths, are discarded

5. A linear regression curve is fit through the remaining rainfall-runoff data, which is used to generate

runoff depths that were discarded earlier

6. The annual monsoon runoff, thus generated, is summed with annual non-monsoon runoff of the

corresponding year to generate the annual runoff series at Andhari G&D site

7. Those years for which the monsoon runoff is generated, non-monsoon runoff is taken as 4.234% of

the monsoon runoff on the basis of gauged runoff at Andhari

8. Yield series obtained at Andhari is converted to that at the Pinjal dam site by weighing the annual

yield at Andhari with the ratio of catchment area of the dam site to that of the G&D site

Yield series at Pinjal dam site is derived for 34 years, i.e. 1975—2008. The 75% dependable annual yield at

Andhari G&D site (see Appendix B.4.1) and the Pinjal dam site (see Appendix B.4.2) are worked out as

527 MCM and 512.3 MCM, respectively, using R-R model. Similarly, the 95% dependable annual yield at

Pinjal dam site is 421.6 MCM.

4.7 Flood Studies

4.7.1 Irrigation Department, GoM

Data pertaining to short duration rainfall and runoff was not available for the Pinjal catchment during the

formulation of this project. A preliminary estimate of the design flood at the proposed dam site was done by

the Irrigation department, GoM, and was based on Synthetic Unit Hydrograph derived by Snyder method.

The magnitudes of one day, two days design storms are listed below:

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a. Rainfall data recorded within the Pinjal catchment:

Particulars Jawhar Mokhada Wada

One day 32.77 cm 39.47 cm 45.92 cm

Two days 50.14 cm 65.84 cm 61.36 cm

b. Rainfall recorded: adjacent Damanganga Valley:

Particulars Madhuban Colony Ratcholi township

One day 56.79 cm 57.30 cm

Two days 72.28 cm 84.41 cm

Recommendation was made to consider the rainfall depths that were recorded at Ratcholi for design

purpose, keeping the maximization factor of 20%. The storm distribution used for the flood study for 48

hours was calculated. Based on these calculations, the peak flood was estimated to be 2,694 cumecs.

4.7.2 Present Flood Study

Methodology adopted for estimating the design flood is based on IS 11223:1985, “Guidelines for Fixing

Spillway Capacity,” and according to the norms proposed by the Central Water Commission (CWC).

According to these guidelines, since the storage capacity of Pinjal dam is more than 60 MCM, it should be

designed for the Probable Maximum Flood (PMF). Accordingly, the Design Flood has been worked out,

using the classical Unit Hydrograph (UG) principle.

It is well-known that the unit hydrograph theory is based on the following four assumptions:

1. Effective rainfall is uniformly distributed over the total catchment area in the specified duration

2. The base of direct runoff hydrograph for different magnitudes of rainfall excesses, but for the same

duration derived from the unit of hydrograph of specified duration, is constant

3. The ordinates of direct runoff hydrograph of common base are directly proportional to the total

quantum of runoff represented by each hydrograph

4. The hydrograph of runoff of a basin for a given period of rainfall reflects the cumulative physical

characteristics of the basin.

In order to adhere to the aforesaid assumptions, the following principle has been used in the following

analysis:

1. Unit period is chosen as 1-hour so that the effective rainfall could be considered uniformly

distributed without appreciable error.

2. For deriving unit hydrograph for a catchment, correct discharge data at sufficiently close intervals

(half hourly, hourly depending upon the size of the catchment) together with concurrent rainfall

data, preferably for isolated flood storms, is essential, at least for a period of three to four years,

covering about 15 events. However concurrent rainfall-runoff data isn’t available for the dam site

but the river discharges are gauged at Andhari river gauging station.

As mentioned in Section 4.1, the rainfall data have been obtained from the State Data Storage Centre

(SDSC), Water Resources Department, GoM located at Nasik. SDSC acts as repositories for all the

hydrological and meteorological data related to major river basins in Maharashtra under the Chief Engineer,

Hydrology-I project. On the diagnosis of the data, it’s observed that short duration rainfall data, in respect of

the raingauges located in and around the catchment, is not available. Due to the paucity of rainfall data, it is

not possible to derive the unit hydrograph strictly by the rational, rainfall runoff equation method or flood

4-9 224604/ENI/IWU/1/0


event based UG. Therefore, it is attempted to generalize the parameters influencing the unit hydrograph

strictly by using Synthetic Unit Hydrograph (SUH) method as per CWC Flood Estimation Report for West

Coast Region sub-zone 5 (a & b).

4.7.3 Derivation of Unit Hydrograph

In the absence of concurrent rainfall-runoff data available for the dam site, unit hydrograph has been

derived using CWC Flood Estimation Report, sub-zone 5 (a & b). This uses the Snyder Method of deriving

a UG. Various parameters of the UG are related to the physiographic parameters of the catchment

concerned, such as the catchment area (A), average slope (S) and length of river (L), through regression

analysis of many catchments in a sub-region. The physiographic parameters for derivation of unit

hydrograph at the Pinjal dam site are worked out using catchment area (A), slope (S) and length of river (L).

The equivalent slope and the derived UG are appended as Appendix B.5.

4.7.4 Design Infiltration Loss and Design Base Flow

Infiltration loss of 0.10 cm/hr and base flow of 0.15 m3/s/sq.km, as recommended in CWC Flood Estimation

Report, sub-zone 5 (a & b), have been adopted.

4.7.5 Design Storm

Details regarding the project-specific storm study by Indian Meteorological Department (IMD), New Delhi,

have been obtained. The Probable Maximum Precipitation (PMP) and time distribution, as per IMD vide

letter dated 31st March, 2010, are taken to consideration. The 1-day PMP value of 80.2 cm for Pinjal dam is

given by the IMD, with clock-hour correction of 15% (attached as Appendix A.5). The clock hour correction

of 0.15 times the storm depth is restricted to a maximum value of 50 mm (Ref: CWC “Recommendation on

Storm Parameters for Design Flood Estimation” – December, 1993).

One-day PMP value of 104.06 mm has also been computed from the CWC’s “PMP Atlas” for West-flowing

Rivers of the Western Ghats. One-day SPS value of 860 mm, based on the 02-07-1941 storm, centred at

Dharampur has been taken corresponding to catchment area of 316 sq.km. A maximisation factor of 1.21 is

used to evaluate the 1-day PMP (see Appendix B.6.6), over which the clock hour correction is applied as

mentioned in the earlier paragraph.

The time distribution of rainfall suggests that 77% of the 24-hour PMP occurs in the first 12 hours of the

storm and the remaining 23% occurs during the succeeding 12 hours (see Appendix B.6.1). Accordingly,

the 24-hour PMP is apportioned to two bells and hourly rainfall distribution in each bell is worked out.

Matching the descending orders of UG ordinates and the excess rainfall of each of the bells separately and

arranging the corresponding rainfall values in reverse order, gives the critical sequence of rainfall, which

produces the maximum flood at the dam site. The rainfall hyetograph corresponding to the PMP is, thus,

obtained by placing the individual bells side-by-side on the time axis. These details are presented in

Appendix B.6.2 and Appendix B.6.4, for IMD-based PMP and CWC-based PMP, respectively.

4.7.6 Convolution

Each rainfall value in the critical sequence, arrived at in the earlier section, is multiplied to the UG ordinates

to obtain direct runoff hydrograph (DRH) for that rainfall. Ordinates of the DRH’s, thus obtained, are

summed up after progressively lagging the individual DRH’s by 1-hour (equal to the rainfall duration). Thus,

the rainfall hyetographs are convoluted through the catchment to obtain the design flood. Based on this

study, a peak flood values of 5,382 cumecs and 6,900 cumecs have been worked out for IMD data and

CWC data, respectively (see Appendix B.6.3 and Appendix B.6.5).

4-10 224604/ENI/IWU/1/0


These values were sent to the CWC to accord its approval. However, the CWC recommended using the

peak flood value arrived at by taking the IMD data, i.e. 5,382 cumecs. The relevant correspondence with

the CWC is attached in Appendix B.6.6.

4.7.7 Conclusion

The Probable Maximum Flood (PMF) of 5,382 m3/s is proposed for Pinjal Dam. A detailed flood study report

has been submitted to MCBM for Pinjal.

4.8 Sedimentation Study

All natural channels of water bring varying amounts of suspended particles/ sediment along with them, from

their respective upper reaches. However, the amount of sediment brought by them varies due to various

reasons. Dams are constructed for two main purposes - to build-up storage behind the dam and to regulate

it as per the project planning. The principal purpose of constructing dams is to store water when it is

available in abundance and utilize the same for hydropower generation, irrigation, municipal water supply or

recreation, according to the purpose for which the dam is constructed. However, sediment deposition in the

reservoir reduces the storage available for water. The rate of silting in a river regime depends on the

climatic conditions, nature of the soil, topography and land-use and hydro-physical conditions of the

catchment. Sediment deposition, by itself, is inevitable. Therefore, sufficient provision of space should be

made in a reservoir for the accumulation of silt load so that its functioning does not get impaired during its

useful life. This necessitates the estimation of the silt load likely to get accumulated over time.

4.8.1 Dead Storage Capacity

The dead storage capacity of a reservoir is its volume corresponding to an elevation below which water

cannot be drawn from the reservoir. Guidelines as per “Fixing the Capacity of Reservoirs – Methods, Part-

2: Dead Storage”, IS 5477 (Part-2):1994, and “Compendium of Silting of Reservoirs in India”, Government

of India, have been taken into consideration, to fix the dead storage capacity of the Pinjal reservoir. No part

of the Pinjal catchment, corresponding to the dam site, is intercepted by any other project. Thus, the entire

catchment area of the Pinjal River up to the dam site, i.e. 316sq km has been considered to estimate the

sediment yield for 50 and 100 years.

4.8.2 Trap Efficiency

Once sediment entering the reservoir is known, the fraction of this load that can be retained/ trapped in the

reservoir needs to be estimated. Trap efficiency, as it is called, depends upon the sediment load

characteristics, the detention time of inflow, and the nature and operation of reservoir outlets. Detention

time is a function of the ratio of storage capacity to inflow, and the shape of the valley. A tentative

estimation of silt load into Pinjal storage and its distribution has been worked out, to know the probable

level up to which silt is getting deposited. This is done in order to facilitate planning the outlet levels for flow

regulation through the reservoir.

4.8.3 Sediment Rate

To estimate annual quantity of sediment deposition, sediment rating curves based on periodic sampling

data is necessary, which is not available for Pinjal Basin. Silt storage required at proposed reservoir on

Pinjal River could not be estimated as per standard procedures; in this background recourse is made to

regional analyses and synthesis. The estimated silt storage for the proposed reservoirs has been arrived at

by the following assessment.

� Borland and Miller have classified the reservoir into four categories, as described in IS 5477 (Part-

II):1994, according to which Pinjal reservoir is determined as Type-III reservoir (Appendix B.7.1).

4-11 224604/ENI/IWU/1/0


� The rate of sedimentation for Pinjal catchment varies from 357 m3/sq.km/year to 524 m

3/sq.km/year, as

per the Manual of Irrigation Works in Maharashtra, published by the Government of Maharashtra. In the

present case, a good forest canopy exists in the Pinjal catchment. Although the catchment has steep

terrain, the silting rate is controlled by putting levee-like structures in its hilly regions. Therefore, a lower

sedimentation rate of 357 m3/sq.km/year was considered during pre-feasibility.

� As per the CWC observations (ref: Appendix B.6.6), the silt rate that was considered (357

m3/sq.km/year) was stated to be on lower side. Hence, a value of 1,790 m

3/sq.km/year as

recommended in Compendium on Silting of Reservoirs in India (2001) for “West flowing rivers beyond

Tapi and South-Indian rivers”), is adopted for estimating dead storage (Appendix A.6)

4.8.4 Total Sediment Volume

Based on the above, estimates of quantities of sediment deposited in Pinjal reservoir are as follows:

1. During 50 years:

Rate of silt deposition = 1,790 m3/sq.km/year

For 50 years, the silt deposition from the catchment area of 316 sq.km =

28.28)1,790)/(10(50316 6=×× MCM

2. During 100 years:

Rate of silt deposition = 1,790 m3/sq.km/year

For 100 years, the silt deposition from the catchment area of 316 sq.km =

5656107901100316 6 .)/(),( =×× MCM

4.8.5 Sediment Distribution

The sediment entering a storage reservoir gets deposited in it with the passage of time, and thereby,

reduces its dead storage as well as its live storage capacity. This causes the bed level near the dam to rise

and the raised bed level is termed as new zero elevation (NZE). It is, therefore, necessary to assess the

revised areas and capacities at various reservoir elevations, such that the assessment can be useful to pre-

plan necessary future changes in reservoir operation, if any. Determining the revised storage-elevation

relationships, based on sediment-loading of the reservoir, also helps in fixing the live storage of the

reservoir and in locating the outlets to withdraw water from it for downstream needs.

Several methods exist for predicting sediment distribution in reservoirs. In this study, two of them, as given

in IS 5477 (Part-II):1994, have been used. They are: (1) Empirical Area Reduction Method, and (2)

Moody’s Method.

4.8.5.1 Empirical Area Reduction Method

Borland and Miller have classified reservoirs into four categories, namely, (a) gorge, (b) hill, (c) flood plain-

foot hill, and (d) lake, based on the ratio of the reservoir capacity to the reservoir depth plotted on a log-log

scale. To compute the type of reservoir, a log-log plot of depth (ordinate) and capacity (abscissa) of the

reservoir has been prepared (see Appendix B.7.1), and the slope of the best-fit straight line is obtained as

0.52. Its reciprocal (= 1.92) classifies Pinjal basin as Type-III (hill).

A design curve is used to estimate the area of probable sediment deposition in the reservoir at different

depths. Equation of the curve is as follows:

4-12 224604/ENI/IWU/1/0


nm

p pCpA )1( −= … (4.4)

where, Ap is a non-dimensional relative area at relative depth ‘p’ above the stream bed, and C, m and n are

non-dimensional constants which have been fixed depending on the type of reservoir.

4.8.5.2 Moody’s Method

This method uses two parameters f(p) and f’’(p) to determine the NZE, as in the following equations:

)(

)(1)(

pa

pVpf

−= … (4.5)

)(

)()('

pHHA

pHVSpf

−= … (4.6)

where, f(p) = a function of the relative depth of reservoir for one of the four types of theoretical design

curves (one each for the type of reservoir)

V(p) = relative volume at a given elevation

a(p) = relative area at a given elevation

f’(p) = a function of the relative depth of reservoir for a particular reservoir and its anticipated

sediment storage

S = total sediment in the reservoir in Ha-m

V(pH) = reservoir capacity at a given elevation in Ha-m

H = total depth of reservoir for normal water surface in m, and

A(pH) = reservoir area at a given elevation in Ha

In Moody’s method, a graph is plotted between the relative depth, p, versus f’(p) as well as versus f’(p). The

intersection point of the two curves gives the NZE value, without the need for any more trials, unlike in the

Empirical Area Reduction method. Thus, Moody’s method is a direct way to find the NZE.

Based on the methods of estimating sedimentation, as described above, the sediment distribution for Pinjal

reservoir has been worked out for two useful-life periods, i.e. 50 years and 100 years. For an original bed-

level of 75.5 m, details of sedimentation analysis based on the two methods mentioned above are as in .

Calculations for arriving at the same are given in Appendices B.7.2—B.7.5.

Table 4.5: Results of Sedimentation Analysis

S.No.

Sedimentation

Rate

(m3/sq.km/y)

Method 50-year

NZE (m)

100-yr

NZE (m)

Trap

Efficiency

(%)

1 357 Empirical Area Reduction 76.25 77.00 99.24

2 357 Moody’s 76.89 77.10

3 1,790 Empirical Area Reduction 83.50 91.28

4 1,790 Moody’s 84.10 90.10

A conservative value of 91.28m has been considered as NZE for further analysis.

5-1 224604/ENI/IWU/1/0


5.1 Demand-Supply

Allocated supply from Pinjal reservoir to Mumbai city is 865 MLD (315.73 MCM). The annual yields at the

proposed dam site as presented and approved by CWC during Hydrological Study Report are 421.6 MCM

and 512.3 MCM, for 95% and 75% dependability respectively. On this basis, reservoir simulation studies

are conducted to fix the storage volume as well as the full reservoir level (FRL).

The capacity-elevation curve at the proposed dam site evolved based on the topographical survey, is

shown in Drawing No. MMD-224604-C-DR-PIN-XX-0006. It is evident that the primary requirement of this

dam is to meet water supply at a constant rate of 865MLD. However, additional water shall be made

available at Pinjal dam from Bhugad and Khargihill dams. NWDA has clarified that constant water supply of

1586MLD shall be made at Pinjal through out the year. The possible alternative demands are analysed as

follows:

� Irrigation: The Pinjal River Project report prepared by the Water Resources Department of the

Government of Maharashtra in the early 1970’s highlights the need for irrigation in the regions

surrounding the proposed dam site.

� Gargai Dam: Dr. Chitale Committee has proposed that the water from Gargai River, also a tributary of

Vaitarna River, may have to be tapped into to meet the future water-supply demand of Mumbai city.

However, around 90% of the course of Gargai River falls within Tansa Wildlife Sanctuary, where

creating a storage reservoir may not be an environmentally feasible option. In this case, the

contemplated water supply from Gargai River to Mumbai city can be drawn from remaining waters of the

proposed Pinjal reservoir, partly or even fully (Reservoir Simulation Studies in Section 5.2 for more

details).

Maximising the storage capacity of the Pinjal reservoir also has another usage. When the reservoir is not

full, it can act as a “detention pond” for Damanganga-Pinjal flows (see Section 4.6.1). D-P Link flows are

envisaged as 1586 MLD or 1.586 MCM per day. Thus, for instance, a 20 MCM of additional storage

capacity in the Pinjal reservoir can detain D-P Link flows for about twelve days.

5.2 Reservoir Simulation Studies

Simulating a proposed reservoir using realistic inflows and outflows is necessary to fix the storage capacity

and control levels of the reservoir, such as the full reservoir level (FRL), the maximum water level (MWL),

the minimum drawdown level (MDDL). Reservoir simulation studies are carried out using available data and

necessary assumptions regarding proposed release patterns. The assumptions made have been described

in this report in the respective sections. The simulation is run for a period of 34 years, i.e. from 1975 to

2008 same as the period for which rainfall-runoff modelling is done.

Inputs to the simulation are as follows:

� Monthly inflows

� Monthly outflows from the reservoir

� Storage-Elevation-Area curves of the reservoir

� Sedimentation and

� Initial reservoir storage

5 Storage Planning

5-2 224604/ENI/IWU/1/0


5.2.1 Inflows

Monthly inflow series for the simulation is derived from the rainfall-runoff model (see Section 4.6). The

annual inflows that are derived from the model are converted into monthly inflows in the same proportion as

that of the monthly inflow series averaged from observed runoff at Andhari G&D site. The values thus

obtained are attached as Appendix B.8.

5.2.2 Outflows

Outflows from the reservoir occur due to various “sinks,” as listed below:

� Outflows appropriated for water supply, irrigation and hydropower.

� Losses during water supply that need to be sourced prior to supply

� Environmental flows that need to be released downstream

� Loss due to seepage from the reservoir

� Loss due to evaporation

5.2.2.1 Dedicated Supply

Pinjal reservoir shall be designed to meet its objective: 100% reliable water supply from Pinjal reservoir to

Mumbai at a constant rate of 865 MLD.

5.2.2.2 Losses During Water Supply

A loss rate of 0.2 m3/s per million square metres of wetted area is assumed for water supply through a

tunnel. Preliminary calculations indicated that a tunnel of about 5.5 m is required to transport the water that

will be taken from the Pinjal reservoir as well as that transferred from Damanganga. Thus, a 0.8% loss of

water by volume is obtained, which is considered to be supplied from the reservoir.

5.2.2.3 Environmental Flows

Creating a storage reservoir on a river stops water from going to its downstream. However, there will

always be life dependent on the waters of this river, downstream of the reservoir.

The committee under CWC on Ecological Flows (for other than Himalayan Rivers) had recommended 0.5%

of 75% dependable annual flow expressed in cumecs. However, this condition was explicitly mentioned for

perennial rivers. Hence, some amount of monthly inflows is left out of the reservoir into the original course

of the river to meet the ecological requirements. This is considered as 10% of monthly inflows in the

simulation study.

5.2.2.4 Seepage

A reservoir usually occupies a huge area and infiltration losses into the soil/ rock on which it sits are

substantial. However, adequate data on seepage losses for the entire submergence area is not available.

Hence, no allowance is made for this loss (IS 5477 (Part-III):1969).

5.2.2.5 Evaporation

Monthly pan evaporation depth (see Section 4.3) data is available for the period 1994—2006. For other

simulation years, i.e. 1975—1993 and 2007—2008, average monthly pan evaporation depth is used to

calculate actual evaporation from the reservoir.

5-3 224604/ENI/IWU/1/0


5.2.3 Storage-Elevation & Area-Elevation Curves

These curves are useful in determining and calculating the storage, corresponding level of water and

corresponding water-spread of the reservoir, in any month of the simulation. Together, they help in

calculating the spills, deficits, evaporation, seepage losses, etc. Reservoir simulation cannot be done

without establishing storage-elevation and area-elevation relationships. Detailed survey data is used to

ascertain these curves, which are attached as Drawing No. MMD-224604-C-DR-PIN-XX-0006.

5.2.4 Sedimentation

Reservoir simulation is carried out, taking into account its sedimentation. IS 5477 (Part-I):1999

recommends considering a new zero elevation (NZE) corresponding to 100-year sedimentation of the

reservoir. Hence, 100-year sedimentation at a rate of 1,790 m3/sq.km/year has been considered and the

most conservative NZE obtained using Empirical Area Reduction method (see Section 4.8.5) is used in the

simulation.

5.2.5 Reservoir Simulation

Reservoir simulation is done for monthly flows and storages. For this purpose, the terminology used is as

per IS 5477 (Part-I):1999. The steps followed for the simulation are as follows:

1. Assume an initial reservoir storage (S00), minimum drawdown level (MDDL) and full reservoir level

(FRL)

2. Add the inflow of first month of the first year (I11), taken from the inflow series generated, to the

storage. The gross storage, thus obtained (−

11S ), is the amount of total water available for that month.

Determine the elevation corresponding to −

11S , −

11L , from the storage-elevation relation.

110011 ISS +=−

… (5.1)

a. If −

11S is greater than the sum of reservoir capacity (SR, calculated from the assumed FRL and

storage-elevation curve) and the required outflow for that month, O11, then, the additional water needs to be “spilled” from the reservoir.

=

=

+−=

+>

−

−

11

1111

1111

Outflow Actual

0Deficit

)( Spill

),( If

O

OSS

OSS

R

R … (5.2)

b. If −

11L is less than the MDDL, then, the gross storage, −

11S , is enough just to fill the reservoir but

no amount of required outflow can be withdrawn from the reservoir.

=

=

=

<−

0 Outflow Actual

Deficit

0 Spill

, If 1111 OMDDLL … (5.3)

c. However, if the gross storage, −

11S , is less than the sum of reservoir capacity and the required

outflow for that month, O11, and if −

11L is greater than the MDDL, then, the actual outflow depends

on whether the active storage (equal to gross storage less the storage corresponding to MDDL,

5-4 224604/ENI/IWU/1/0


“the inactive storage”) is able to fulfil the required outflow demand or not. This is depicted in the following equations.

=

=

=

>>+<−−

11

11111111

Outflow Actual

0Deficit

0 Spill

, & & )( If

O

OSMDDLLOSS AR … (5.4a)

=

−=

=

<>+<−−

A

AAR

S

SOOSMDDLLOSS

Outflow Actual

Deficit

0 Spill

, & & )( If 1111111111 … (5.4b)

d. In determining the required outflow, the water-spread corresponding to −

11L is estimated from the

area-elevation relationship, which is used to calculate the evaporation volume for that month from the corresponding pan evaporation value used.

e. Thus, the actual outflow, Oa, and the net storage of water left in the reservoir, +

11S , are

determined.

11,1111 aOSS −=−+

… (5.5)

3. +

11S acts as the initial storage for the second month of the same year, for the simulation, −

12S , and so

on.

4. Step 2 is repeated progressively for all the months of the simulation.

5. The reliability, R, of the reservoir is defined as the ratio of number of years during which deficits in one or more months occurred, ND, to the total number of years of simulation, N. It is expressed as a percentage.

%100×=

N

NR D

… (5.6)

6. As per IS 5477 (Part-I):1999, a reservoir built for the main purpose of water supply must be designed for 100% reliability. Therefore, if the reliability is less than 100%, one of the following steps can be taken and the simulation is repeated:

a. Increase the storage capacity of the reservoir: Since a lesser storage capacity may lead to more spills, increasing the former may conserve water that is otherwise spilled for usage during deficit periods, thus increasing reliability.

b. Reduce the MDDL: Reducing the level from where water is drawn from the reservoir increases its active storage, thus increasing the ability of the reservoir to deal with deficit periods more effectively. Thus, this measure increases reliability.

Many trials of reservoir simulation may be required to arrive at an economical storage capacity and MDDL, while maintaining 100% reliability as well as giving enough room for the sediment to settle (dead storage).

5.2.6 Impact of Assuming Initial Reservoir Storage on the Simulation

As a major fraction of annual inflows into the reservoir occur during four monsoon months (June—

September), and since the reservoir storage capacity assumed is close to 95% dependable annual flows,

5-5 224604/ENI/IWU/1/0


the inflows almost match the reservoir storage capacity most of the time. Thus, the different values of initial

storage assumed did not affect the end result of simulation studies.

The calculation-sheet of one of the reservoir simulation studies is attached as Appendix B.9. An abstract of

important findings from the simulation is given in Table 5.3.

5.3 Reservoir Storage

From the past studies carried out by the Government of Maharashtra (GoM), a full reservoir level (FRL) of

141.00 m has been proposed for the Pinjal dam. The gross and live storage capacities were fixed as

413.57 MCM and 401.55 MCM respectively. However, the 95% dependable yield at dam site is 421.6

MCM.

Further, it is observed, from analysis of toposheets surrounding the submergence area, that there is a

possibility of increasing the storage capacity of the reservoir to a higher value than that fixed by the GoM,

without any negative impact in terms of submergence related resettlement and rehabilitation (R&R). This

would facilitate additional storage either to meet the partial irrigation demands previously envisaged OR

provide buffer storage to meet other demands such as industries. These details are further explained

below.

The gross storage capacity of 483 MCM is now planned at an FRL of 145 m MSL. Accounting for

sedimentation, a live storage capacity (above NZE of 91.28 m) of 473.10 MCM shall be available. However,

the MDDL calculations that are governed by the head requirements of transmission tunnel for water supply,

which is explained in subsequent sections.

The adequacy of this storage capacity is determined from reservoir simulation studies. Another variable that

needs to be fixed yet is the invert level of outflow openings from the reservoir. In case no invert level

satisfies the desired outflows, as per Section 5.2.2, the storage capacity shall be increased and the

reservoir simulation carried out again. However, it is found from the simulation that the storage capacity that

is fixed above satisfies the outflow demands adequately for an outflow opening invert level determined as

given below.

5.4 Intake Invert Level

In general, fixing the invert level of intake works/ intake invert level (IIL) of a dam is governed only by the

sedimentation criterion: the IIL is placed slightly above the NZE determined by sediment deposition

calculations. However, every project is unique and there may be other criteria that govern the IIL. One such

criterion in this project is the hydraulic design of the connecting link tunnel from the proposed Pinjal

reservoir to Gundovili

5.4.1 Pinjal-Gundovili Link

Water taken from the Pinjal reservoir is routed to a treatment facility at Bhandup Complex, via Gundovili,

through multiple tunnels, which are currently in different stages of planning, design and construction. The

Pinjal—Gundovili Link (PGL) is envisaged as a tunnel, about 63 km long, the intake point of which will be

close to the proposed dam site on Pinjal River. From hydraulic back-calculations made through the

Bhandup—Gundovili—Pinjal linkage, it has been established that the minimum hydraulic grade line (HGL)

of flow at the Pinjal-Gundovili tunnel intake must be MSL 103.83 m. Thus, although sediment deposition

consideration allows the IIL at Pinjal dam to be located at around 94 m, the Pinjal-Gundovili Link HGL

governs the IIL, which equals 106.87 m, from hydraulic considerations.

Therefore, considering this restriction on fixing the IIL, reservoir simulation studies are carried out to

determine the same.

5-6 224604/ENI/IWU/1/0


5.4.2 Availability of Water for Alternate Uses

Satisfying 100% reliability for water supply requires the IIL to be as low in the reservoir as possible, while

the HGL restriction on the IIL places a bottom limit on its location. Thus, to determine whether 100%

reliability can be achieved with a higher IIL, reservoir simulation was carried out. It is found from the

simulation that the maximum IIL that can be achieved at 100% reliability, with a water supply of 865 MLD,

equals 122.01 m (MSL). This is greater than the minimum IIL of 106.87 m, arrived at from HGL

considerations.

Therefore, by lowering the IIL to 106.87 m, it is found from the reservoir simulation that 1,219.5 MLD of

water can be supplied from the reservoir at 100% reliability. Thus, apart from the 865 MLD that is required

to be supplied to Mumbai, 354.5 MLD of surplus water is available for alternate uses, such as irrigation/

bulk industrial needs.

5.4.3 Potential Utilisation of Buffer Storage

Due to the HGL consideration, the IIL from Pinjal dam has been kept at 106.87 m, which is much higher

than the new zero elevations (NZE), considering different sedimentation scenarios (see Table 5.1). Thus, in

this case, a large fraction of inactive storage corresponds to buffer storage.

Table 5.1: Buffer Storage Scenarios

S.No. Sedimentation

Rate (m

3/sq.km/y)

Number of Years

(y)

New Zero Elevation

(m)

Intake Invert Level (m)

Buffer Storage (MCM)

1 0 75.50 53.0

2 50 84.10 37.2

3

1,790

100 91.28

106.87

19.0

This buffer storage can be utilised for alternate needs. However, in every case the water supply demands

must be met. This requires effective management of spills from the reservoir, which is possible if a

Reservoir Operation Policy is developed. More detailed reservoir simulation must be done to develop

operation policies, which is left as a future prospect to explore.

5.4.4 Abstract of Reservoir Simulation

Various scenarios of reservoir operation have been evaluated through reservoir simulation studies (see

Section 5.2). A brief of the assumptions made for performing reservoir simulation study is given in Table

5.2. A few important results taken from the studies, to design the dam and its appurtenant structures are

presented in Table 5.3.

Table 5.2: Input to Abstract of Reservoir Simulation

S.No. Input Parameter Value Units

1 Years of simulation 34 years

2 Sediment Rate 1,790 m3/sq.km/y

3 Years of sedimentation 100 years

4 Corresponding NZE 91.28 m

5 Conveyance loss rate 0.2 m3/s/Msq.m

6 Conveyance loss (% of outflow) 0.8 %

7 Environmental flows as a fraction of monthly inflows

10 %

5-7 224604/ENI/IWU/1/0


Table 5.3: Abstract of Reservoir Simulation

S.No.

Full Reservoir

Level

(m)

Gross Reservoir Capacity

(MCM)

Net Water

Supply*

(MLD)

Intake Invert Level

(m)

Reliability

(%) Comments

1 865 122.01 100

2 1,219.5 100

Maximum possible IIL at 100% reliability

3 1,300 88

4 1,400 74

5

145.00 483.0

1,500

106.87

71

*In addition to the considered environmental flows, conveyance, seepage and evaporation losses, as mentioned above

5.5 Hydropower Potential

In view of the power shortage in Maharashtra and the emphasis power generation business has received in

recent years, it is prudent to consider the possibility of power generation from the storage reservoir. As per

the present scope, the potential for hydropower generation for the proposed storage created at Pinjal is

briefly explored. The HGL elevation at Pinjal-Gundovili Link intake shall be 103.83 m, whereas the FRL at

Pinjal dam is 145.0 m. Therefore, a maximum operational head of about 41 m (during monsoon period) is

available to generate hydropower at the project site. Considering the shortage of power in the country, the

proposed hydro-electric power (HEP) plant is planned as a base-load station, instead of a peaking-power

station, since water is to be supplied to Mumbai city at 100% reliability.

5.5.1 Demand of Electricity in India

The power sector of India has grown in power generation from 1300 MW capacity during Independence to

102,907 MW, due to efforts of the Government of India (GoI) to regularly allocate funds and add to

capacity. However, in spite of the GoI’s plans, the present power availability is not enough to cater to the

needs of the country, as there is a peak shortage of power of around 10,000 MW (13%) and 40 billion units

of energy deficit (7.5%).

The GoI has made plans for a capacity addition of 100,000 MW by 2012 to solve the problem of shortages.

In the following table, it can be seen that capacity addition is a high priority for the government.

Table 5.4: Growth of Hydropower Capacity

Actual or Estimated Installed Capacity at

the End of Plan Period Plan Period

Total (MW) Hydro (MW)

Planned

Hydropower as %

of Planned Total

Power

9th plan (1977-98 to 2001-02) 108,362 29,593 27

10th plan (2002-03 to 2006-07) 160,034 40,025 25

11th plan (2007-08 to 2011-12) 212,107 61,613 29

12th plan (2012-13 to 2016-17) 279,000 84,000 30

13th plan (2017-18 to 2021-22) 370,000 115,000 31

Year 2022-23 to 2025-26 463,000 150,000 32

5-8 224604/ENI/IWU/1/0


The Central Electricity Authority has, more recently, made an assessment that there will be significant

power supply deficiencies in the country in next decade. The proposal of Pinjal HEP project, therefore,

proposes to assist in addressing this shortfall.

The need for developing the hydropower potential of this project is, therefore, demonstrated by the shortfall

in power supply, together with the increased attractiveness of the project relative to water supply project

actually taken up by the Municipal authorities. It is anticipated that the Pinjal HEP plant may either supply

power to the Western grid or may be used as a captive power station for the electricity needs around the

dam and its colonies.

5.5.2 Power and Energy Studies

Power and energy studies have been conducted to determine the potential hydropower benefits of the

water supply scheme, using the same proposed water supply intake. For this study, a simulation model,

that combines reservoir simulation and hydropower simulation, has been used to determine the main

scheme parameters, such as the installed capacity, average effective head available for power generation.

The details of the model used are given in the following sections.

Energy generation for a hydropower scheme should be determined for a 90% dependable annual yield. It

can be seen from the runoff series (Appendix B.4.2) that the 90% dependable annual yield is 444.5 MCM,

which closely matches with the yield during the year 1995—96. The water supply scheme is designed to

supply 865 MLD from Pinjal reservior and 1,586 MLD of Damanganga—Pinjal flows. Thus, a total of 2,451

MLD of water shall be supplied to Mumbai city via the Pinjal-Gundovili Link. Thus, these releases are used

to assess potential power generation.

Table 5.5: 90% Dependable Flows for Power Generation

Inflows

(MCM)

Minimum Discharge available for Water

Supply cum Power Generation Month

Pinjal Flows Damanganga Flows (cumecs)

July 225.53 48.98 28.3

August 73.15 48.98 28.3

September 56.29 47.40 28.3

October 51.00 48.98 28.3

November 25.55 47.40 28.3

December 0.00 48.98 28.3

January 0.00 48.98 28.3

February 0.00 44.24 28.3

March 0.00 48.98 28.3

April 0.00 47.40 28.3

May 0.00 48.98 28.3

June 71.39 47.40 28.3

5.5.3 Head for Power Generation

Joint reservoir simulations are carried out to calculate the reservoir levels in different months by considering

90% dependable inflows and desired outflows. The FRL and the IIL of the reservoir are fixed at 145 m and

106.87 m, respectively. Based on these values, the maximum, minimum and average gross heads work out

to 31.30m, 17.41m and 25.56m, respectively. The average head available for 90% dependable inflows is

considered to calculate the power potential.

As per IS 12800 (Part-III):1991, the HEP plant is designed to be operative within 0.65 to 1.25 times the

average design head, the details of which are given in Table 5.6.

5-9 224604/ENI/IWU/1/0


Table 5.6: Limits of Hydropower Generation

Dependable Inflows

(%)

Average head available for

HEP generation

(m)

Minimum Drawdown Level

for HEP

(m)

Maximum Reservoir

Elevation for HEP

(m)

90 25.56 123.44 138.78

The minimum drawdown level and the maximum reservoir level, as calculated above, are based on the tail-

water level, the average value of which is taken as 106.83 m.

5.5.4 Head Loss Calculation

A penstock designed as per IS 11625:1986 and IS 4880 (Part-III):1976, shall convey water from the

reservoir to the hydraulic machinery installed in the HEP plant. The non-overflow cross-sectional details,

along with the penstock arrangement, are shown in Drawing No. MMD-224604-C-DR-PIN-XX-00012

Head loss in this water conductor system must be accounted for, to estimate the power generated more

accurately. Two methods are commonly used to calculate the expected head loss in a water conductor

system:

1. Manning’s formula

2. Darcy-Weisbach formula

The calculation of head loss using Manning’s formula has been popularly used in India. The same has been

adopted in this study, because the values of the Manning’s roughness coefficient, n, have been established

for different materials with reasonable experience and confidence. Calculation of head loss is presented in

Appendix B.11. It is observed that head losses in the water conductor system are of the order of 1.265 m.

5.5.5 Installed capacity

Installed capacity of the powerhouse has been selected based on the following considerations:

� Assessment of energy generation with various installed capacities

� Utilisation of designed flows for water supply from Pinjal dam to Mumbai

� Incremental value of energy generation with the increased installed capacity

� Annual load factor

The effect of installed capacity has been examined in detail to work out the optimum size of the project for

maximising power generation without affecting continuous water supply to Mumbai city. Power potential

study has been carried out for different installed capacities ranging from 1 MW to 12 MW with an increment

of 1 MW. These calculations are detailed in Appendix B.12.

Figure 5.1 shows the annual energy generated at different installed capacities, for 90% dependable flows.

It can be seen from the figure that the increase in power generation is very steep till about 7 MW and

further rise is gentler. After 7 MW of installed capacity, no significant increase in generation is seen. Thus,

the installed capacity of the power plant has been selected as 8 MW (2×4 MW) with an annual plant load

factor of 72%.

5-10 224604/ENI/IWU/1/0


Figure 5.1: Installation Capacity for Hydropower

8.76

17.52

26.28

34.91

41.84

47.2550.37 50.48 50.48 50.48 50.48 50.48

0

10

20

30

40

50

60

0 1 2 3 4 5 6 7 8 9 10 11 12 13

Installed Capacity (MW)

An

nu

al E

ne

rgy

Ge

ne

rate

d (

GW

h)

5.5.6 Size of Generating Units

The size of generating units is based on the following constraints:

1. Only 865 MLD of water will be supplied from the Pinjal reservoir during the initial phase of its

development. The additional 1,586 MLD of Damanganga-Pinjal Link flows will be available after about

7-8 years after Pinjal dam development.

2. Maintenance and rehabilitation cycles of the installed units that generate power shall not interfere with

the water supply to Gundovili in any case.

Thus, keeping in view the above constraints, three (3) units of 4 MW each have been proposed for this

project. Of these three, one shall be acting as a standby unit, allowing for maintenance of another unit.

Initially, for the duration when Damanganga-Pinjal Link is not ready, only two units of 4 MW each may be

commissioned, one of them acting as a standby unit. Eventually, a third unit may be added to the HEP

plant.

5.5.7 Annual Energy Generation

Annual energy generation for the 90% dependable annual inflows (Damanaganga and Pinjal), with an

installed capacity of 8 MW, is limited to 50.48 GWh. If there are no Damanaganga flows, the annual energy

generation considering Pinjal inflows shall be 17.87 GWH. This is because the discharge used for power

generation is fixed by the downstream supply from the reservoir. The only variable in power generation is

the head available in the reservoir at a given point of time. By installing the powerhouse, additional benefits

are being created for the project.

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6.1 Geotechnical Investigation

This section describes the geotechnical fieldwork and laboratory testing carried out as part of this study.

Geotechnical investigations were undertaken at the Pinjal dam site in July 2009, as part of the foundation

assessment for Pinjal storage dam. Twelve bore-holes were drilled on the proposed dam alignment. The

locations of these bore-holes represent key points of the dam structure. Disturbed as well as undisturbed

soil samples and rock samples were collected, which were then inspected and logged. The entire

geotechnical investigation report is attached as Appendix A.7. Important results of the investigation are

extracted from the Report and are presented in the following sub-sections:

6.1.1 Subsurface Soil Profile

The subsurface soil profile shows yellowish brown silty clay, followed by weathered rock. Details of the soil

profile are as in Table 6.1.

Table 6.1: Subsurface Soil Properties

S.No. Tests Values Units

1

Sieve Analysis:

Gravel

Sand

Silt

Clay

7.43

54.16

15.97

22.44

%

2

Atterberg Limits:

Liquid Limit

Plastic Limit

Shrinkage Limit

Plasticity Index

43.73

23.48

17.07

20.25

%

3 Specific Gravity 2.68 -

4 Natural Moisture

Content

15.655 %

5 Dry Density 1.62 g/cm3

6.1.2 Bed Rock

Bed rock is encountered at the shallow depth of 3 m to 5 m with core recovery (CR) and rock quality

designation (RQD) as high as 77% and 71%, respectively. Test bores indicate foundation quality rock at

about 1.5 m close to the river bed. For the spillway proposed in the main river gorge, good quality exposed

rock is available. The foundation grade line of the dam will mainly rest on amygdaloidal basalt massive trap

and, in some portions, on volcanic bracia. The bed rock shows very good unconfined compressive strength

and point load index, with and without saturation of 7 days. Rock mass rating (RMR) values are also

obtained from laboratory tests and field observations.

6 Dam Studies

6-2 224604/ENI/IWU/1/0


Average rock properties are as given in Table 6.2.

Table 6.2: Rock Properties

S.No. Rock Particulars Values

1 Density 2.27g/cm3

2 Water absorption 2.07%

3 Specific gravity 2.30

4 Porosity 1.38%

5 UCS 116.02 kg/cm2

6 Young’s Modulus 132,000 kg/cm2

7 Poisson ratio 0.24

8 Abrasion value 24.4%

Relatively newly-formed rocks that are free from structural defects have high compressive strengths.

Characteristic strengths of rocks of different types encountered at dam site are depicted below in Table 6.3.

Table 6.3: Uniaxial Compressive Strength of Rock Specimens

S.No. Location Greyish Amygdaloidal Basalt

(kg/cm2)

Compact Basalt

(kg/cm2)

1 Dam Alignment

Right bank 1,079-1,523 1,139-2,278

2 Dam Alignment

Left bank 997-1,467

3 Spillway

4 Gorge 1,383-2,440

6.2 Type of Dam

Dams may be classified into a number of categories, depending upon the purpose for which they are built

(water supply, flood mitigation, etc.), their use (diversion, storage, etc.), size (high, low, small, large, etc.),

hydraulic design (overflow & non-overflow), and materials used for their construction (earthen, rock-fill,

gravity, arch, etc.). According to usage, dams are classified as storage dams or diversion dams. Storage

dams are built for serving various purposes like municipal water supply, irrigation, hydropower generation,

recreation and/or flood control. Diversion dams, on the other hand, are built to create head in a river to

divert water for conservative purposes, through a head regulator. The purpose for which a storage dam is

built will influence its design. Based on the hydraulics, dams are classified as overflow dams and non-

overflow dams. However, the most common classification of a dam is based upon the material used to build

the structure. Various types of dams, differentiated based on the material used for their construction, and

the way each type of dam withstands the reservoir-imposed loading is briefly discussed in the following

sub-sections.

6.2.1 Earthen Dam (Homogeneous or Zoned)

Earthen dams are the most common type of dams, the construction of which involves use of natural and

locally available materials that require minimum processing. There is no stringent policy with regard to the

foundation grade rock and its characteristics for building earthen dams. However, construction of the dam

requires special type of soil from specifically marked borrow areas.

Earthen dams may be homogeneous or zoned. In a homogeneous earthen dam, naturally available earth is

used and it is ensured that hydraulic gradients are within the body of the dam. In zoned dams, impervious

hearting and pervious shell material are used, impregnating with chimney sand filter and drainage

arrangements. Seepage through the foundation can be reduced by providing cutoff trench filled with

6-3 224604/ENI/IWU/1/0


impervious material or by providing diaphragm walls. Adequate free board needs to be provided to avoid

overtopping of earthen dams.

Earthen dams require appurtenant structures to serve as spillways, outlet works, etc. The design procedure

involves pseudo static analysis in which the slopes, berms, etc. are worked out for a critical slip circle to

satisfy the factor of safety criterion for upstream and downstream slopes under different conditions.

6.2.2 Rock-fill Dam

Rock-fill dams use rocks of different sizes to provide stability and an impervious surface membrane to

achieve water tightness. Surface membranes may be concrete, asphalt or any other durable material. A

rubble cushion is provided between the main rock-fill and the upstream impervious membrane. A cutoff wall

is provided at the upstream toe of a rock-fill dam to create a watertight connection between its surface

membrane and foundation. Rock-fill dams require a foundation which does not settle and rupture the

watertight membrane. Rock-fill dams are suitable to remote locations, where supply of good rock is ample

and where the scarcity of soil for constructing an earthen dam. Stability analyses of rock-fill dams are

carried out by wedge analysis and the slopes are worked out. Like earthen dams, the rock-fill dams also

need appurtenant works to avoid overtopping and its consequent damages.

6.2.3 Gravity Dam

Gravity dams are a favourite choice when hard rock, with minimal fault planes, is available at a reasonable

depth, to bear its enormous weight. Gravity dams may be aligned straight or curved, its simplest theoretical

cross-section being a right-angled triangle. The main principle of the gravity dam design is that the forces

acting against it are resisted by its own weight, such that the resultant of all the forces acting on the dam

passes through middle third of its base. The dam must withstand various combinations of stresses, that

arise as a result of corresponding loading conditions, as per IS 6512:1984. Experience has shown that

reinforced concrete dams are costlier in comparison to roller-compacted concrete dams. Therefore, in the

recent past, gravity dams are being constructed using roller-compacted concrete.

Roller-compacted concrete (RCC) dams can be designed and constructed rapidly as well as economically.

This is because the RCC dam construction technology is based on highly mechanised activities of

transporting RCC, placing, spreading and compacting, which results in a faster construction process. The

method of design of RCC dams is also simpler, compared to a more elaborate method of designing other

types of dams. This is also one of the keys to completing RCC dams quickly and economically, while

maintaining adequate quality. Simpler dam design also allows its builder to construct the dam in a

continuous and speedy manner. RCC construction sequences and their timing play a significant role for the

continuous construction progress, particularly during wet seasons, with regard to the placement speed,

construction schedule, and river diversion considerations. The river diversion problems can be handled with

ease, as after the initial portion is constructed, spillages of water during frequent flash floods can be

permitted to overtop the constructed portion of the dam without planning for any additional diversion.

6.2.4 Arch Dam

In sites where the abutments are strong with good rock and the river is narrow and deep, arch dams are

preferred. Loads are transferred to the foundation through the abutments; thus, the section of the dam is

generally slender, compared to that of other types of dams. However, such sites rarely exist, limiting the

construction of arch dams.

6-4 224604/ENI/IWU/1/0


6.2.5 Selection of Type of Dam

Topography and catchment properties provide quantitative information regarding water availability or yields

at the proposed dam site. This parameter has a significant influence on the choice of type of dam, design,

and environmental and social issues, like rehabilitation and resettlement.

In case of Pinjal dam, in the region surrounding the proposed dam site, rock is available at shallow depths

and there is less soil cover over hard rock. Therefore, there would be shortage of locally available hearting

materials within reasonable lead. Moreover, the catchment corresponding to the selected site falls in a

heavy rainfall zone, where there is a possibility of large flows in the river within a small duration, which may

not be able to be bypassed through the diversion works. Thus, an earthen or a rock-fill dam will not be

suitable at this location. In such a site, roller-compacted concrete gravity dam is the most suitable. Thus,

the proposed dam is designed as a Roller Compacted Concrete Gravity structure.

6.3 General Layout of the Dam

Pinjal dam consists of the following components:

1. Diversion works

2. Dam in the main gorge

3. Dam in the saddle

4. Spillway on the right flank of the main gorge

5. Energy dissipation arrangements

6. Construction sluice

7. Hydropower arrangements

8. Bypass arrangement for water supply works

Description and provisions for these components for the proposed dam is in the following sections. A brief

view of the entire layout of the dam and its appurtenant works is given in MMD-224604-C-DR-PIN-XX-

0007.

6.3.1 Control Levels of the Project

6.3.1.1 Free Board

Free board is the vertical distance between normal pool elevation and top of the dam. Free board

calculations are carried out as per IS 10635:1993, which are included in Appendix B.10.

6.3.1.2 Control Levels

Some of the important control levels of the project are as listed in Table 6.4.

Table 6.4: Control levels of Pinjal Dam

S.No. Particulars Levels

(in metres; MSL)

1 Top of Dam (TOD) 148.000

2 Full Reservoir Level (FRL)/

Maximum Water Level (MWL)

145.000

3 Spillway Crest Level (SCL) 133.000

4 Intake Invert Level (IIL) 106.870

5 River Bed Level (RBL) 75.500

6-5 224604/ENI/IWU/1/0


6.4 Diversion Works

Regardless of the type of dam, whether concrete or embankment types, it is necessary to de-water the site

for final geological inspection, foundation improvement and for the construction of the first stage of the dam.

In order to carry out the above works, the river has to be diverted temporarily. It is, hence, proposed that

the river be diverted during the initial stages of the construction of the dam.

6.4.1 Coffer Dam

Diversion channels are often classified according to the type of diversion namely, single stage or multiple

stage diversion scheme. In the former, which is more suitable for narrow valleys, the same set of diversion

channel and coffer dams is utilized throughout the period of construction. In the latter, however, the

channels and coffer dams are shifted from place to place in accordance with phasing of the work. A single

stage diversion is proposed for constructing this dam.

6.4.2 Diversion Tunnel

As sufficient overburden and good rock is found along the proposed diversion route, river diversion can be

done by constructing a diversion tunnel, to divert water from upstream of the river to downstream of the

river, without causing damage to the storage structure.

A concrete dam is allowed to get overtopped during floods when construction activity is not in progress. The

resulting damage is either negligible or could be tolerated without much concern. Therefore, it is customary

to adopt a diversion flood that is just adequate to be handled during the non-monsoon season, when the

construction activity of the dam is continued. Generally, the largest observed non-monsoon flood or non-

monsoon flood of 100 year return period is adopted as a diversion flood. As there is no non-monsoon flood

data available at the proposed dam site, the design flood assumed for the diversion works is 1% of the

design flood considered for designing the spillway of the dam, which equals 54 m3/s.

A tunnel of 5.0 m diameter is proposed to allow passing of this flood. Hydraulic calculations to arrive at the

same are presented in Appendix B.13. A tentative alignment of the diversion tunnel is shown in Drawing

No. MMD-224604-C-DR-PIN-XX-0007

6.5 Dam & its Appurtenances

The Pinjal dam alignment has been fixed based on the latest survey data, which would provide an

economical section of the gravity structure. The alignment is nearly perpendicular to the flow direction in the

main river course. Total length of the dam (including Overflow and Non-overflow sections) is 545 m and the

average dam height is 41.2 m. A spillway is proposed on the right flank of the dam. The main dam consists

of 36 monolith blocks of 15 m each.

6.5.1 Foundation

The induced stresses on the foundation rock, due to weight of the dam and other loads at this site is about

150-200 t/m2 (= 15-20 kg/cm

2). Although the characteristic strength of rocks (see Table 6.3) is very high

compared to the anticipated dam loads, presence of faults in the rock mass affects its overall behaviour. It

is, however, found that even for low RMR values there is a considerable factor of safety for the anticipated

dam loads. Accounting for all these factors, the foundation depths for various sections of the dam structure

have been fixed, based on 70% core recovery of foundation rock, as given in Table 6.5.

6-6 224604/ENI/IWU/1/0


Table 6.5: Foundation Depths of the Dam

S.No. Chainage

(m)

Ground

Level (GL)

(m MSL)

Bore-

Hole

Number

CR

(%)

RQD

(%)

RL at 70%

CR and RQD

(m MSL)

Dam Foundation Level

below GL

(m)

1 180 137.830 10 85 85 135.300 2.53

2 210 120.701 5 71 71 113.200 7.50

3 240 108.356 6 97 97 100.900 7.46

4 270 100.384 7 67 67 88.900 11.48

5 330 81.163 8 87 87 73.660 7.50

6 360 77.163 9 97 97 70.260 6.90

7 390 76.311 12 77 75 71.810 4.50

8 420 75.500 2 77 65 71.000 4.50

9 450 78.574 3 69 63 73.300 5.27

10 480 81.571 4 65 65 73.570 8.00

11 510 83.500 1 96 96 71.000 12.50

12 600 103.493 11 69 69 99.000 4.49

6.5.2 Non-Overflow Section

The non-overflow (NOF) section of the dam stretches between chainage (Ch.) 160 m to Ch. 595 m and Ch.

675 m to Ch. 705 m, along the axis of the dam. The length of NOF section is 465 m, with a proposed top

width of 12 m. The downstream side of NOF is provided with a slope of 0.9H:1V. The average heights of

the non-overflow section on the left side and the right side of spillway are 52.3 m and 13.6 m, respectively.

Cross-sectional details of a NOF section are shown in MMD-224604-C-DR-PIN-XX-0010.

A shallow gorge/ breach section is located between Ch. 1710 m and Ch. 1900 m, the elevation at its

deepest point being 136.83 m at Ch. 1800 m. In this stretch of 190 m long, roller-compacted concrete

(RCC) gravity-type non-overflow dam section is proposed, the top of which is at 148.0 m. Thus, the

maximum height of this dam section is 11.4m. The proposed top width of this section is 10.0 m, with a slope

of 0.9H:1V on its downstream face. Cross sectional details of this NOF section are shown in Drawing No.

MMD-224604-C-DR-PIN-XX-0011. Plan and elevation of the same can be seen in Drawing No. MMD-

224604-C-DR-PIN-XX-0008

6.5.2.1 Stability Analysis

The sections of Overflow (OF) and Non-overflow (NOF) are designed based on BIS Codes IS 6512, IS

6934, IS 1893, to withstand hydrostatic, hydrodynamic, silt, wave and likely seismic forces. Stability

analysis of the Non-overflow section is carried as single block without considering the lateral anchorage

due to abutments and anchorage reinforcement driven into the foundation rock.

The following requirements and assumptions have been considered in design criteria, according to IS

6512:1984.

� The overflow section should be adequate enough to carry the design flood without causing any

destruction to the dam structure and its components

� Stress transfer from body structure to the foundation should follow elastic laws; they should act as an

inseparable monolithic structure

� Unit length of dam as a slice between two vertical planes normal to the base has been considered for

analysis, without lateral stress transfers to the abutments

� The governing criteria for stability are the factor of safety against over turning and sliding

� No movement of foundation due to load transfer

� The concrete body of NOF/OF structures is homogeneous, isotropic and uniform elastic material

� No differential movement takes place either at foundation or in the body of dam

6-7 224604/ENI/IWU/1/0


� All loads are carried by gravity action

� The normal stress variation from upstream to downstream or vice versa is uniform and linear

Table 6.6: Parameters considered in design of Pinjal Dam

S.No. Material Values Adopted

for Design

1 Roller-compacted concrete 24 kN/m3

2 Water 9.81 kN/m3

3 Silt 3.6 kN/m3

4 Earth quake coefficient 0.04

5 Uplift 100%

6 Angle of internal friction over rock 42º

7 Wind velocity at FRL 138.3 km/h

8 Seismic coefficient Zone III

9 Importance factor 3

Various Forces:

Various forces considered for the design as per IS 6512:1984.

� Self weight of dam

� Horizontal water pressure

� Weight of water on upstream inclined face of the dam

� Uplift force at the base of the dam section

� Wave pressure

� Weight due to piers and bridge for overflow section design

� Wind forces

� Seismic forces as per IS 1893:1984

Load Combinations:

IS 6512:1984 defines the following load combinations

1. Load combination B:

Normal Operating Condition: Full reservoir elevation, normal dry weather tail water, normal uplift and silt.

2. Load combination C:

Flood discharge condition Reservoir at MWL, all gates open, normal uplift, and silt.

3. Load combination E:

Load Combination ‘B’ with earthquake but no ice

4. Load combination F:

Load combination ‘C’ but with extreme uplift (drains inoperative)

5. Load combination G:

Load combination ‘E’ but with extreme uplift (drains inoperative)

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Load combination ‘G’ is considered in the current design. Based on these adverse load combinations, and

using appropriate safety factors, the stability analysis has been carried out. Permissible stresses adopted

are as per the provision in IS code for concrete construction. The stability analysis of NOF and OF sections

is carried out on the basis of provisions contained in IS 6512:1984 and suitable dimensions that provide

adequate stability to the dam are adopted. Detailed calculations of stability analysis are attached as

Appendices B.15, B.16 and B.17. A summary sheet, highlighting the critical stresses is attached as

Appendix B.18.

6.5.3 Overflow Section

Before designing the overflow section of a dam, the type of spillway, its location and energy dissipation

arrangements (EDAs) downstream of the spillway are fixed, based on the recommendations of IS

10137:1982. A cross-sectional view of the OF section is given in Drawing No. MMD-224604-C-DR-PIN-XX-

0009. Plan and elevation of the same can be seen in Drawing No. MMD-224604-C-DR-PIN-XX-0008.

6.5.3.1 Location of the Spillway

The main parameter considered for the location of the spillway is the cost of the Energy Dissipation

Arrangements (EDA’s), which need to be tested through model experiments based on IS 4997:1968 and IS

7365:1985, and gate operational ease during floods. The possible spillway locations at the proposed dam

site are

a) main gorge,

b) one of the dam’s flanks, and

c) saddle.

If the spillway is located in the main gorge, high head of water creates very high velocities at the spillway

toe, requiring lengthy, expensive and special EDA. On the other hand, locating the spillway in the flanks

need long guide- and spray- walls to train the flow into the natural river channel. However, at the proposed

dam site, since there is good rock available at shallow depth, envisaging minimal guide-walls, the spillway

is proposed to be located on the right flank of the dam.

The location of spillway is studied in conjunction with the EDA, which are suitably provided based on the

following:

a) Tail-water rating curve and jump rating curve

b) Height and length of guide walls

c) Provision of spray walls

Energy dissipation arrangements normally provided are:

a) Horizontal type (USBR Type-I to Type-IV), when the tail-water rating curve and the jump rating

curve do not differ by more than 10% (IS 4997:1968)

b) Roller/ Slotted bucket type, where the jump rating curve lies below the tail-water rating curve.

c) Trajectory bucket type, where there is deficiency in tail-water and good foundation grade rock is

available

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At the proposed dam site, steep slopes along the downstream of the spillway (around 1 in 15) as well as

that of the main river course (around 1 in 750) do not allow tail-water to pool to large depths. Moreover,

there is good rock found at shallow depths at the dam site. Therefore, a trajectory bucket-type energy-

dissipation device is proposed.

The existing ground profile downstream of the proposed spillway section may need to be excavated to

allow for an apron to avoid any scouring immediately downstream of the spillway. Provision of a concrete

apron of nominal length of 15m downstream is recommended to prevent the scour near the bucket lip (IS

6934:1998 and IS 10137:1982). Training walls extending beyond the end of the buckets generally serve to

guide the flow into the river channel to protect the wrap-rounds of the adjacent river banks.

6.5.3.2 Design of Ogee Spillway

An overflow section is proposed in the main gorge of the river, on the right flank of the dam, from Ch. 595.0

m to Ch. 675.0m. Good foundation grade rock is available at shallow depth and accordingly the foundation

level will be kept in sound rock where anticipated core recovery is equal to or greater than 70%.

The bed level of river at the spillway location varies from 103.47 m to 130.08 m. The crest level of spillway

is fixed at RL 133.0 m with downstream slope of 0.9H:1V. An Ogee-shaped crest spillway is used, which is

made to conform closely to the shape of lower nappe of an aerated, free-flowing jet of water over a sharp-

crested weir, the head over its crest being equal to the design head of the spillway. The shape of upstream

and downstream profile is designed as per IS 6934:1998. Details of the Ogee profile are attached as

Appendix B.14.

6.5.3.3 Energy Dissipation Arrangements

Therefore, the spillway has been designed with its surface having an Ogee profile and trajectory bucket-

type of energy dissipation arrangements. The bucket is provided with a radius of 20 m, the lip making an

angle of 30° with the horizontal (IS 7365:1985). The elevation of the bucket lip is kept at an elevation of

102.60 m. The flow coming down the spillway is thrown away from its toe to a considerable distance of

128m to downstream as a freely discharging upturn jet which is then trained into the main course of the

river, thereby avoiding excessive scour immediately downstream of the spillway. Detailed calculations are

attached in Appendix B.14. The hydraulic load per sq m of bucket surface is calculated as 16.72 t/m2,

which is less than the permissible maximum theoretical pressure of 18t/m2 as specified in IS 7365:1985

EDAs are shown in Drawing No. MMD-224604-C-DR-PIN-XX-0009

6.5.3.4 Spillway Gates

An ungated spillway is not economically viable because it requires increasing the dam height, in addition to

increase in length of the overflow section to pass the design flood, thereby increasing the submergence

area on the upstream side of the dam.

Flood routing studies are done based on Modified Pul’s method, to pass the design flood of 5,382 cumecs

through the spillway gates by fixing suitable spillway length and gate dimensions, as per IS 11223:1985.

The results are shown in Table 6.7:

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Table 6.7: Spillway Gate Dimensions

Effective

Length,

L (m)

Head over

Spillway

(m)

Number

of

Spans/

Gates

TOD

(m)

MWL

(m)

Crest

Level

(m)

Flow

through

Gates

(cumecs)

61 13.0 5 148 145 132.0 5910.19

70 12.0 5 148 145 133.0 6014.87

78 11.0 5 148 145 134.0 5882.20

90 10.0 5 148 145 135.0 5883.00

105 9.0 5 148 145 136.0 5860.16

114 8.5 5 148 145 136.5 5839.69

125 8.0 5 148 145 137.0 5846.57

138 7.5 5 148 145 137.5 5859.05

153 7.0 5 148 145 138.0 5857.26

From the above calculations, five (5) radial gates of size 14.0 m×12.0 m are chosen, which would

effectively discharge the design flood with minimal submergence.

The spillway consists of four (4) RCC piers, designed to be 2.5 m wide (along the dam axis). Thus, the

overall length of the OF section of the proposed dam is (70+4×2.5 =) 80 m. They are rested on good

foundation grade rock available in the spillway location. Their structural design should be done as per IS

13551:1993. Further, details like staircase and lift well, road bridge, instrumentation, etc. are proposed as

per the standard practice. The gates are operated using hydraulic hoists. Reinforced cement concrete

(RCC) road bridge of 7.5 m width is proposed all along the dam axis.

6.5.4 Construction Sluice

Sluices are provided in the body of the dam mainly to release regulated supplies of water for a variety of

purposes. During initial stages of construction of a concrete dam, construction sluices can be used to

release flood waters, or to allow passage of non-monsoon flows without hindrance to the construction

activity. Construction sluices are also useful to operate in drought conditions. As per IS 11485:1985,

purposes of sluice are mentioned below briefly:

� River diversion

� Irrigation

� Generation of hydro-electric power

� Water supply for municipal or industrial uses

� Pass flood discharge in conjunction with the spillway

� Flood control regulation to release water temporarily stored in flood control storage space

� Depletion of the reservoir in order to facilitate inspection of the reservoir rim and the upstream face of

the dam for carrying out remedial measures, if necessary;

� Furnish necessary flows for satisfying prior right uses downstream; and

� For maintenance of a live stream for abatement of stream polation, preservation of aquatic life, etc.

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Thus, in the current case, a horizontal construction sluice of diameter 3.5 m is proposed at Ch. 405.0 m

(Drawing No. MMD-224604-C-DR-PIN-XX-0007).

6.5.5 Training Walls

Training walls along the sides of the spillway are constructed to contain and manage flows from the

spillway. Therefore, it must be higher in elevation than the profile of the highest possible flow. A free-board

of at least 2.50 m is given above the trajectory of the jet that is thrown from the spillway.

Training walls are also provided along the sides of the flow from the apron, downstream of the spillway, to

the Pinjal river course (Drawing No. MMD-224604-C-DR-PIN-XX-0009)

6.5.6 Galleries

The height of the dam is 76.50 m over the foundation grade rock. As per IS 10135:1985, it is obligatory to

provide a drainage gallery when the dam height exceeds 20 metres above foundation grade rock. A

foundation gallery is proposed to collect seepage water from the body of the dam so as to reduce uplift, and

to facilitate easy inspection of dam so as to monitor the structural behaviour of the dam. It is so located so

that it is as close as possible to the foundation grade rock line. The minimum concrete cover over the

foundation grade rock to the bottom of the foundation gallery is about 1.5 m.

A foundation gallery of size 2 m×2.5 m has been proposed in the body of the dam. The provision of 2.25 m

height is to facilitate transporting grouting equipment to place curtain grouting and to drill drainage holes.

The upstream face of foundation gallery is kept in line with the upstream face of the dam. As per IS 12996

(Part-I):1992, the foundation gallery must be at a distance of the maximum of 5% hydrostatic head and 3m,

from the upstream face of the dam. Hence, the galleries are provided at a distance of 3.5 m from the

upstream face of the dam.

As per IS 12996 (Part-I):1992, two inspection galleries of 1.5 m×2.25 m each are proposed above the

foundation gallery, at intervals of 26 m. Thus, these three galleries are located at elevations of 74 m, 100 m

and 126 m, wherever possible. Where ground elevations do not permit continuity of a gallery, it is

discontinued and connected, by a vertical shaft with a ladder, to a higher gallery.

Drainage holes, running vertically from the inspection galleries towards the foundation gallery, are proposed

at 3 m (centre to centre) to carry water seeping into the galleries safely downstream.

6.5.7 Grouting & Drainage

Grouting is proposed to reduce the deformability of jointed or shattered rock and to reduce the permeability

of the foundation rock. Foundation grade rock at the proposed dam site is amygdaloidal compact basalt,

which is watertight in nature and may not require elaborate treatment. However, some dykes are present in

the foundation rock, which may have linked with small cracks in it. Therefore, to seal any rock crevices and

plug excessive seepage of water, consolidation grouting within the upstream 1/3rd

of the base width is

proposed. Grouting is done until required Lugeon values are achieved, which may require secondary and

even tertiary grouting to be done (IS 6066:1994).

As per the geotechnical report (Appendix A.7), curtain grouting is required for the foundation rock at the

dam site. Single line grout curtains with a primary spacing of 12 m are proposed. For secondary and tertiary

grouting, if necessary, it can be reduced to 6 m and 3 m, respectively. Curtain grouting can be done from

the foundation gallery, with 75 mm diameter holes up to a depth equal to 75% hydrostatic head (= 52 m).

The depth of the grout curtain depends upon the type and conditions of the rock mass with respect to its

permeability. As per IS 11293 (Part-II):1993, the empirical formula, D = [(2/3)×H + 8] is used to calculate

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the depth of curtain grout (D), where H is the maximum hydrostatic head. Therefore, the depth of the

curtain grout is arrived as 55 m below drainage gallery.

Drainage from the foundation rock into the foundation gallery relieves uplift pressures on the dam

foundation. Normally, the depth of a 75 mm diameter drain-hole is about two thirds of that of curtain grout,

i.e. (2/3)×55 = 36 m. Drainage holes must be drilled only after the curtain grouting is completed.

6.5.8 Contraction Joints

The proposed concrete gravity dam is very long (545 m), measured along the dam axis from one bank of

the river valley to the other. Therefore, to relieve thermal stresses on the dam structure, it is necessary to

divide it into blocks, along the transverse direction, and to fill the gaps by providing transverse contraction

joints.

The dam structure is divided into 36 monolith blocks of 15 m each. A standard copper water seal is

proposed on upstream side. A PVC water-stop is proposed on downstream side between dam blocks.

Positioning and design of these water-stops is as per standard practice (IS 12200:2001 & IS 15058:2002).

6.5.9 Instrumentation

Normally, instruments are installed in a concrete gravity dam to measure the various parameters that

indicate the structural health of the dam and the state of the foundation. These instruments have been

classified into two types: obligatory and optional measurements, by IS 7436 (Part-II):1997.

6.5.9.1 Obligatory Measurements

� Uplift pressure at the base of the dam at a sufficient number of transverse sections

� Seepage into the dam and appearing downstream there-from

� Temperature of the interior of the dam

� Displacement measurements.

− Those determined by suspended plumb lines;

− Those determined by geodetic measurements where warranted by the importance of the structure

− Those determined by embedded resistance joint meters at contraction joints where grouting is

required to be done

6.5.9.2 Optional Measurements

The following measurements are optional and may be undertaken where warranted by special

circumstances of project. These would be beneficial for high dams, for structures of unusual design, for

structures where unusual or doubtful foundations exist, for the verification of design criteria and for affecting

improvement in future designs:

� Stress

� Strain

� Pore pressure (as distinct from uplift pressure), and

� Seismicity of the area and dynamic characteristic of the structure.

Surveillance of seismic environment of the project site needs special attention in case of large dams to

know about the seismicity of the region before taking up construction. Creation of a reservoir generates

additional load on the surrounding area and underlying geological strata. Thus, it becomes essential to

know the change in the seismicity pattern, if any, due to creation of the large reservoir. The behavior of dam

during an earthquake also needs to be assessed. For these purposes, a seismological laboratory may be

established near the project site.

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6.5.10 Lighting, Ventilation and Other Facilities Inside the Dam

Ventilation, lighting, water supply, air supply, sanitation, fire-fighting system, telephone, elevators, first aid,

etc. may be provided in the proposed dam, as per IS 9297:1979.

Ventilation pipes of 500 mm diameter are proposed at 50 m (centre to centre). They start at roofs of the

galleries provided and emerge from the downstream face of the dam section (see Drawing No. MMD-

224604-C-DR-PIN-XX-0009)

6.5.11 Hydropower Works

Details of hydropower generation are given in Section 5.5. Location of the powerhouse can be seen in

Drawing No. MMD-224604-C-DR-PIN-XX-0007. Three (3) numbers of turbines, designed to produce 4 MW

each, are installed at the proposed hydro-electric power (HEP) plant. A tentative arrangement of the plant is

presented in Drawing No. MMD-224604-C-DR-PIN-XX-0013.

6.5.12 Bypass Arrangement

As described in Section 5.5.3, there is a range of effective water head within which hydropower generation

will be economical. However, if the reservoir water elevations are out of this range (presented in Table 5.6),

economical operation of the HEP plant may not be possible. Additional studies are required to be done to

determine the exact limits on the effective head available, for efficient hydropower generation.

In the absence of these studies, a bypass arrangement is proposed to supply water to Gundovili at 100%

reliability (see Drawing No. MMD-224604-C-DR-PIN-XX-0007). Additional energy present in the water

drawn without producing electricity needs to be dissipated to bring the HGL at Gundovili tunnel intake to

103.83 m. Further studies are required to be done to ascertain this arrangement.

6.5.13 Infrastructural Works

A 7.5 m wide road way is proposed along the dam axis, for 465 m length of non-overflow section of the

dam, which also connects to the nearby access roads. An RCC road bridge of 7.5 m wide of 80 m length

above overflow section is proposed.

Other major infrastructural works, like access/ approach and diversion roads, colonies, etc. are discussed in

the following sub-sections:

6.5.13.1 Access Road and Internal Roads

The dam is located 1 km away from Khidse village. In order to transport men and material required for

construction as well as post-construction operation and maintenance of the dam, it is necessary to connect

the dam site to the nearest state highway or other major roads. Further, various pathways, called internal

roads, are necessary for their movement to various parts of the dam site. Internal roads are proposed at

different levels from bed level to top of the dam for easy access of the entire site during construction. They

facilitate onsite inspection, installation of machinery, carrying construction material, etc. The total length of

the proposed access as well as internal roads is about 3.69 km (see Drawing No. MMD-224604-C-DR-PIN-

XX-0007). Out of this, stretches of about 1.97 km may be dismantled after construction.

6.5.13.2 Diversion Road

An existing road connecting Barpachwadi and Jhap from Pinjal, which is about 39.6 km long, will get

submerged due to formation of Pinjal reservoir. In order not to disturb existing connectivity between towns/

villages, is suggested to divert the submerging stretch of the existing road, based on the FRL of 145 m.

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Thus, new diversion roads have been proposed from Pinjal to Barpachwadi (20 km) and from Pinjal to Jhap

(14.5 km). Therefore, the total diverted route is around 34.5 km long.

The width of the proposed road is planned to be 5.0 m, with a 4 m-wide carriageway and 0.5 m wide

shoulders on both sides of the road. A maximum gradient of 1V:20H has been restored for short stretches

of the road alignment. A wearing course of 40 mm thick asphaltic concrete over a 50 mm thick base course

of bituminous macadam has been considered throughout. Sub-base course of WBM would have a

thickness of 150 mm in cutting. In rest of the alignment, the ruling gradient is limited to 1V:50H.

6.5.13.3 Housing Colony

For effective implementation of the project, concerned personnel are proposed to be located near the

construction site. Hence, it is required to construct a staff colony, offices, stores etc. nearby the dam. A

housing colony is proposed on the left bank of the Pinjal dam for 15 families. It will have telecommunication

lines, internal roads, electric supply, sewage disposal arrangement and water supply connections, in

addition to other common facilities. 2 houses out of the provided 15 are reserved as guest houses, in order

to facilitate accommodating officials visiting the dam site.

6.5.13.4 Electrical Power Supply

Arrangements for electrical power required during construction of the dam and allied works, along with the

maintenance of the colony, form a major part of infrastructure works. By referring to projects of similar

nature, which are located in Maharashtra, a tentative power requirement for the colony and dam is

considered as 2 MVA and 3 MVA, respectively. This power requirement at the site is proposed to be made

available by establishing substations, one near the housing colony and the other at the dam location. The

substation located at the housing colony would cater to the needs of the staff quarters, water supply

system, road lighting etc. and the substation at the dam would cater to the needs of dam construction

machinery, site lighting, dewatering pumps, etc.

6.6 Salient Features

Select salient features of the proposed Pinjal dam, including aspects of hydrology, engineering and design

are shown in Table 6.8.

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Table 6.8: Salient Features

Description Value Units Comments

HYDROLOGY

Catchment area up to the G&D site is 327 sq.km

Catchment area up to the proposed dam site is 316 sq.km

Annual catchment yield up to Andhari G&D site at 75% dependability 527 MCM

Annual catchment yield up to Andhari G&D site at 95% dependability 442 MCM

Annual catchment yield at 95% dependability at dam site 421.6 MCM

Annual catchment yield at 75% dependability at dam site 512.3 MCM

One-day PMP used for design 80.2 cm Provided by the IMD

Design Flood 5,382 cumecs

RESERVOIR CHARACTERISTICS

River bed level 75.5 m

Full reservoir level 145.0 m

Gross storage at proposed Pinjal dam site 483 MCM

New Zero Elevation, considering 1,790 m3/sq.km/y for 100 years 91.28 m

New Zero Elevation, considering 1,790 m3/sq.km/y for 50 years 84.10 m

WATER SUPPLY

Rate of water supply from Damanganga to Pinjal, considering supply all round the year 1,586 MLD

Rate of water supply from Pinjal to Gundovili, considering supply all round the year 865 MLD

Total rate of water supply via the Pinjal project to Gundovili, considering supply all round the year 2,451 MLD

RESERVOIR SIMULATION STUDIES

Maximum invert level of the intake, considering 865 MLD supply at 100% reliability 122.01 m

Maximum water supply rate at 100% reliability, considering the intake invert level at 106.87 m 1,219 MLD

Surplus water available for alternate uses, considering the intake invert level at 106.87 m 354 MLD

HYDROPOWER

Installation capacity for Pinjal flows only (865 MLD) 4 MW

Installation capacity for flows via Pinjal project (2,445 MLD) 8 MW

Size of units 4 MW/unit

Number of units 3 - One standby unit

Total installed capacity 12 MW

Annual energy generation 50.48 GWh

Plant load factor 72 %

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Description Value Units Comments

OVERFLOW SECTION

Type of spillway Ogee -

Minimum foundation level 98.5 m

Total length of spillway 80.0 m

Effective length of spillway 70.0 m

Number of piers 4 m

Width of piers 2.5 m

Spillway crest level 133.0 m

Width of road bridge 7.5 m

Energy dissipation arrangement Trajectory-

bucket -

Bucket invert level 100.0 m

Bucket radius 20.0 m

Bucket lip angle (with horizontal) 30.0 degrees

Gate dimensions (Radial Gates) 14.0×12.0 m

NON-OVERFLOW SECTION (Main Gorge)

Type of dam (Roller Compacted Concrete) Gravity -

Height of dam from deepest foundation level up to FRL 75 m

Length of dam 465.0 m

Top of dam 148.0 m

Top width of dam 12.0 m

Invert level of intake for water supply 106.87 m Governed by Gundovili

HGL

NON-OVERFLOW SECTION (Shallow Gorge)

Type of dam (Roller Compacted Concrete) Gravity -

Height of dam from minimum foundation level up to FRL 11.4 m

Length of dam 190.0 m

Top of dam 148.0 m

Top width of dam 10.0 m

7-1 224604/ENI/IWU/1/0


National Environmental Engineering Research Institute (NEERI) is currently undertaking an EIA/EMP

analysis of Pinjal Dam. However, the current study provides an insight into the baseline methodology to

assess environmental, social impacts and mitigation measures involved.

Impacts of dams and reservoirs onto the environment and society are diverse in nature, ranging from being

temporary and short term to permanent and long term. Hence, selection of a dam site becomes an

important step, which helps in minimising the environmental and social impacts caused due to dam

construction at Pinjal River. Given below is the list of various environmental and social impacts, which

would be caused as a result of dam construction.

7.1 Baseline Conditions

1. Inundation of Natural Habitats: Due to creation of reservoirs, there may be a loss of endemic and rare

species of flora and fauna, sometimes even resulting in extinction of a few species. The loss, however,

would be mostly seen in terrestrial habitats than in aquatic habitats.

2. Deterioration of Water Quality: The quality of water in the river could be deteriorated, compared to the

original river water quality, due to reduced oxygenation in a reservoir compared to that in running

waters. Moreover, stagnant waters in a reservoir allow detention and concentration of pollutants.

Anaerobic decay of biomass in the reservoir, due to lack of sunlight penetrating its deeper layers, may

result in biological stratification (a condition caused due to lack of oxygen in the deeper layers of the

reservoir).

3. Water-borne Diseases: Infectious diseases can spread around the reservoir, due to stagnant waters

breeding mosquitoes and other insects, and presence of unclean surroundings in the vicinity of the dam

site. Diseases like dysentery and cholera are common because of presence of contaminated water.

4. Aquatic Life: Reservoirs have major effect on fish and other aquatic life. Major impacts include blocking

of upstream fish migration and hindrance to downstream fish migration. Many endemic fish and other

aquatic species cannot adapt to artificial lakes. Changes in downstream river flow pattern severely

impact the fish, as a result of water quality deterioration. In extreme cases, it may result in killing the

fish species and thereby damaging aquatic habitats due to low oxygen levels.

5. Reservoir Sedimentation: Sediment transport downstream of a river and its deposition on the Plains is

responsible for the fertility of the soil. Due to sediment-trapping nature of a reservoir, downstream soil

fertility is affected.

6. Access Roads: New roads constructed to access the dams can result in the major land use changes.

Deforestation is a major factor caused due to the road construction, in turn contributing to a loss of

biodiversity, accelerating erosion and other environmental problems associated with it.

7. Loss of Cultural Property: Places with archaeological and historical importance could be at risk and

may be destroyed as a result of construction of roads, borrow pits and other miscellaneous works

associated with dam construction.

7 Environmental & Social Issues

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8. Displacement of People: Major adverse social impacts of dams are the involuntary displacement of

people. This may have impacts on the environment because of conversion of natural habitats to places

suitable for accommodating people who are displaced. Moreover, all the above environmental impacts

may affect the livelihoods and life styles of those depending on them. For example, fishermen

dependent on the river waters will be drastically affected due to a reduction in fish yields of the river

downstream of a dam.

The process from clearing the site for construction of a dam to successful working of the dam, at the

proposed dam site, would impact the environment of the site and surroundings, apart from the socio-

economic conditions existing within. Therefore, there are a lot of ways in which constructing a dam on a

natural water course adversely impacts environment and society. Some of the above mentioned aspects

are dealt with in more detail in the following sections. For this purpose, dam construction has been

categorised into three phases. They are: pre-construction phase, construction phase and operational

phase. The chosen dam site, along with the land-use pattern, is shown in Drawing No. MMD-224604-C-DR-

PIN-XX-0003

7.2 Environmental Conditions

The environmental impacts assessment consists of three phases mentioned below:

1. anticipate the environmental impacts

2. monitoring of the impacts

3. management of the assessed impacts

7.2.1 Pre-Construction Phase

The factors considered while selecting the site for Pinjal dam construction are as follows:

a. whether the site is prone to flash floods

b. frequency of occurrence

c. areas getting affected

The evacuation and clearance of the dam site is an important step for Pinjal dam construction. This step is

necessary for the foundation in hard rock, spillway, hydro-electric powerhouse, tail-race channel and other

infrastructure works, and placing the evacuated soil/rock in a dump area. In order to process this action for

the proposed dam site, blasting materials like gelatin sticks, ammonium nitrate and electronic detonators

would be used, which contribute towards environmental degradation – noise, water and air pollution.

Land clearance for Pinjal dam construction in the chosen dam site would result in release of pollutants like

NOx, SO2 gases and Particulate Matters, apart from fugitive emissions as a result of blasting and crushing

of stones for land clearance. Materials used for the construction would be brought from Kalyan or Thane to

the site: a distance of about 90 km, by heavy vehicles. Transportation of materials, would contribute to air

pollution as a result of vehicular emission as well as dust. Noise pollution is another problem caused as a

result of blasting, usage of construction equipments and crushers, with assessment becoming an essential

step.

Deforestation and land clearances are another segment in the pre-construction activity affecting not only

land but also air and noise quality as well. It results in loosening of the soil cover thus contributing towards

increased sedimentation, soil erosion, loss of soil fertility and flash floods. This limits the storage capacity of

the reservoir and robs downstream waters off sediment.

Another factor to be considered during the pre-construction phase is the migration of fish. As a result of

impoundments of the Pinjal River by the proposed dam, there occurs a physical change in riverbeds

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resulting in a change in physico-chemical environment and in cutting upstream-downstream linkages. This

barrier affects migration of fish species.

Presence of archaeologically and historically important monuments within the submergence area must also

be mapped and taken care of, before starting the construction.

7.2.2 Construction Phase

This phase involves transportation of materials to the dam site and construction process. Various raw materials used during this phase include water, steel, cement, fly-ash, wood, glass, paints, polyvinyl chloride (PVC), rubber, etc. Transportation of these materials using heavy vehicles induces the noise, water and air pollution. Similarly, it would affect the groundwater and soil quality as well, in case of any leakage of fuel from the vehicles transporting the construction materials.

Clearing the land cover, for construction, results in a loss of rare species of flora and fauna, if any.

The length of roads being submerged, due to creation of Pinjal reservoir, is around 42 km. Construction of

new roads to replace the submerged ones increases the environmental footprint of the project. River

diversion is another necessary step to de-water the site for final geological inspection, foundation

improvement and for the construction of the initial stages of the dam. This involves blasting rock to create a

5.0 m diameter tunnel, which creates noise, water and air pollution. Establishment of a temporary workers’

colony on the site would lead to release of sewerage and chances of spread of water borne diseases are

high in these areas. A disposal plan of solid waste and effluents must be carefully planned and strictly

adhered to during construction. Otherwise, chances of deteriorating the water quality present in the chosen

site will be high.

7.2.3 Operational Phase

The Pinjal dam would be constructed keeping the FRL to 145.0m. The lake that would be formed by the

storage on Pinjal River will stretch over a length of 5.4 km. The reservoir once built would tend to change

the temperature of the water present in it. This results in temperature variation in water resulting the water

to be cooler in summer and warmer in the winter, than it would be without being in the dam. Since this

water would flow into the river, the altered temperature would change the temperature of the water present

in the river. Therefore, it would impact the plant and animal life present both in the reservoir as well as in

the river, creating environment that is unnatural to the local species.

Reservoir sedimentation and deforestation impacting the endemic species of plants and animals are a few

of the common problem areas during this phase.

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Thus, to sum up, Table 7.1 showcases the environmental impacts of three phases.

Table 7.1: Environmental Impacts

Parameters Impacts Expected

Pre-Construction Phase

Air quality Release of SO2, NOx and other pollutants as a result of blasting during site

evacuation. Fugitive emissions due to crushing; vehicular emissions

Water quality Disposal of effluents at various location of sites; release of sewerage

Land environment; soil

erosion

Deforestation and land clearance for construction of various other

infrastructure facilities apart from the reservoir

Loss of soil fertility; flash floods

Noise quality Blasting and construction equipments; crushing of the stones

Aquatic ecology Changes in the river; change in the physicochemical environment, thus

affecting the various species that are dependent on the river

Barrier across the river, thus affecting the routes for migration

Pubic health water

borne disease

Increased chances of outbreak of water borne disease in the workers colony,

lacking the sewerage treatment

Construction Phase

Air quality Usage of raw materials for the construction of the dam; transportation of

these materials to the project site; dust emissions

Land Environment Loss of rare species of flora and fauna from the project site

Water quality Effluents released from various sources like worker camps, crushers etc

released into main stream

Noise level quality Noise from the equipments used

Muck disposal and solid

waste

Muck generated from the chosen dam site and allied activities

Solid waste would be released from the worker’s colony

Public health safety;

Solid waste

management

Minor accidents may occur at the project site during construction phase;

generation of solid wastes from the workers colony

Operational Phase

Catchment area Reservoir sedimentation occurrence chances at higher rate

Terrestrial ecology

Deforestation resulting in loss of endemic species of plants and animals

present in the site.

Aquatic ecology Changes in physical and chemical characteristics of the river would affect the

local species of plants and animals as well as those present in the river

7.2.4 Environmental Monitoring Plan

For analysing air, water, land and noise levels, for the chosen dam site at Pinjal River, methodologies

adopted have to be clearly specified. The land-use/ land-cover pattern of the chosen alternative site has to

be determined using Remote Sensing studies, satellite imagery, and topographic sheets, together with

establishing the ground-truth. Standard methods ought to be used for categorizing the flora and fauna

involving detailed field survey.

To regulate air quality, air quality monitoring stations have to be established for regular checking done 24

hours as per the National Ambient Air Quality Standards, issued by the Central Pollution Control Board

(CPCB). Air monitoring stations have to be established, within a radius of 10 km from the Pinjal Dam site,

covering villages present upstream, downstream. Measurement of air quality would be done during pre-

monsoon, post-monsoon and winter seasons. As per the CPCB, concentration limits of various pollutants,

to be measured using time weighted average, are given in Table 7.2.

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Table 7.2: CPCB Pollutant Concentration Limits

Pollutants

Time for calculating

weighted average

(hours)

Concentration in

Ambient Air

(µg/m3)

SO2 24 80

NOX 24 80

PM 10 24 100

PM 2.5 24 60

Similarly, noise quality should also be calculated based on the standards by National Ambient Noise Quality

Standards (NANQS) with establishment of noise monitoring stations within 10 km radius of the Pinjal Dam

site, located both upstream and downstream.

Water quality has to be regulated continuously for both surface and ground sources taking many

parameters to consideration. These parameters include pH, Dissolved Oxygen, Biochemcial Oxygen

Demand (BOD) for periods of five or seven days, Chemical Oxygen Demand (COD), Absorption Ratio, total

coliform organisms, Electrical Conductivity, etc. as given by the World Health Organization. Minimum of 10

samples have to be collected for assessing the quality of surface and ground water. The samples should be

collected from the dam site and villages located within a radius of 10 km.

Classification of water has been done by CPCB, based on the purpose for which it is used, as listed in

Table 7.3:

Table 7.3: Classification of Water

Water

Class Purpose Criteria

Class A Drinking water source without

conventional treatment but after

disinfection

• Total Coliform organisms MPN/100 ml shall be 50 or less

• pH between 6.5 and 8.5

• Dissolved Oxygen 6 mg/l or more

• BOD 2 mg/l or less

Class B Water for use for organized outdoor

bathing

• Total Coliform organisms MPN/100 ml shall be 500or less


• Dissolved Oxygen 5mg/l or more


Class C Waters for use as drinking water source

with conventional treatment followed by

disinfection

• Total Coliform organisms MPN/100 ml shall be 5000 or less

• pH between 6 and 9



Class D Waters to maintain aquatic life • pH between 6.5 and 8.5


• Free ammonia (as N) 1.2 mg/l or less

Class E Waters for irrigation, industrial cooling

and controlled waste disposal


• Electrical conductivity less than 2250 mico mhos/cm

• Sodium absorption ratio less than 26

• Boron less than 2 mg/l

The collected samples are to be sent for testing to verify whether the water existing at the Pinjal dam site is

in compliance with the standards and is safe for further consumption. Other factors, like assessment of soil

quality and meteorological aspects have to be monitored as a part of environmental monitoring for the

chosen alternative.

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A Catchment Area Treatment Plan should be designed and monitored with the aim of delineating micro-

watersheds in the river catchment and mapping of areas which are significantly degraded requiring various

biological and engineering treatment measures. Usage of Remote Sensing and GIS should be done to

identify such areas. This plan must be prepared year-wise, with physical and financial details.

Major forest land that would be submerged covers an area of 6.45 sq. km which is around the Pinjal Dam

site. Based on the Catchment Area Treatment Plan, afforestation and establishment of greenbelt is an

essential step to be taken into consideration to make up for the loss of forest area. This activity has to be

performed in consultation with Maharashtra State Wildlife Department.

A Disaster Management Plan has to be planned while designing the dam and before undergoing

construction, taking different conditions into consideration. Various parameters like evaluation of a disaster,

such as advance knowledge of occurrence of flood due to dam break, vulnerability analysis, hazard area

mapping and likely effects on life and property, etc. have to be considered. Public Health Delivery System is

another scope in this phase, where identification of possible threats due to dam construction and other

activities have to be identified. Suitable mitigating measures have to be implemented, like regular health

checkups and programs for checking endemic diseases for the people involved with the dam constriction.

Environmental parameters that have to be monitored are given in Table 7.4.

Table 7.4: Environmental Parameters to be Monitored

Item Parameters Frequency Location

Construction Phase

Air Quality SO2, NOX, CO2, SPM (PM10 and

PM2.5)

24 hourly for two

alternate days in a

month for every

quarter during

construction period or

as per the norms of

Central Pollution

Control Board

(CPCB)

Following

locations:

• Construction

Site

• Ongrichapada

• Vire

• Khidse

• Ujjani

(anticipated

villages within an

area falling under

10 km radius)

Ambient Noise Level Equivalent Noise Level 24 hourly for two

alternate days in a

month for every

quarter during

construction period or

as per the norms of

Central Pollution

Control Board

(CPCB)

• Construction

Site

• Ongrichapada

• Vire

• Khidse

• Ujjani

(anticipated

villages within an

area falling under

10 km radius)

Surface Water Quality pH, temperature, turbidity, Free

Ammonia, Biological Oxygen

Demand (BOD), Chemical

Oxygen Demand (COD), Na,

Absorption Ratio, Total coliform

organisms, Electrical Conductivity

One sample every

quarter till the

construction period

• At Dam site

• Nearby

villages

7-7 224604/ENI/IWU/1/0



Drinking/ Ground

Water Quality

Temperature, pH, Conductivity,

Odour, Taste, Turbidity, Oil and

Grease, BOD, COD, Dissolved

Oxygen (DO), Total Dissolved

Solids (TDS), Sodium, Potassium,

Sulphites, Potassium and

Phosphorus, Water holding

capacity, porosity, total hardness,

Sodium, Potassium, Calcium,

Sulphites, Chlorides, Fluoride,

Lead, Iron, Faecal Coliform and

Total Coliform

One sample every

quarter till the

construction period

1 sample to be

collected from the

worker’s camp

water supply site

Nearby villages

Soil Quality Particle size distribution, Texture,

pH, Electrical Conductivity, Cation

exchange capacity, Sodium

Absorption Ratio (SAR),

Permeability, Water holding

capacity, Porosity, Nitrogen,

Potassium and Phosphorus

One sample in every

season for every

quarter till the

construction period

• 1 sample near

dam site

• 1 sample at

muck disposal

site

• 1 sample at

worker’s camp

site

Ecology Terrestrial and Aquatic Entire project site

Meteorological

aspects

Wind direction, velocity,

temperature, humidity, rain

At one of the

ambient air quality

sampling sites

Operational Phase

Surface Water Quality pH, temperature, turbidity, Free

Ammonia, Biological Oxygen

Demand (BOD), Chemical

Oxygen Demand (COD), Na,

Absorption Ratio, Total coliform

organisms, Electrical Conductivity

Once in every

season (pre

monsoon, monsoon

and post monsoon)

• Reservoir

• Nearby

villages

within an area

falling under 10 km

radius

Drinking/ Ground

Water Quality

Temperature, pH, Conductivity,

Odour, Taste, Turbidity, Oil and

Grease, BOD, COD, Dissolved

Oxygen (DO), Total Dissolved

Solids (TDS), Sodium, Potassium,

Sulphites, Potassium and

Phosphorus, Water holding

capacity, porosity, total hardness,

Sodium, Potassium, Calcium,

Sulphites, Chlorides, Fluoride,

Lead, Iron, Faecal Coliform and

Total Coliform

• Sample from

project colony

• Nearby

villages

within an area

falling under 10 km

radius

Erosion and siltation Soil erosion rates and slope

stability of embankments of dam,

efficacy of soil and conservation

measures

According to the

Catchment Area

Treatment Plan

River bank of

Pinjal

Terrestrial ecology Status of afforestation, program of

greenbelt development, changes

According to the

Catchment Area

Dam location and

its surroundings

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in migration patterns of the

terrestrial fauna

Treatment Plan (within an area

falling under 10 km

radius)

Aquatic ecology Status of phytoplankton,

zooplankton, benthic life, fish

composition, changes in migration

patterns of the aquatic fauna

species

According to the

Catchment Area

Treatment Plan

Dam location site

7.2.5 Environmental Management Plan

7.2.5.1 Pre-Construction Phase

In order to manage the impacts identified, necessary steps shall be taken. As mentioned earlier, this phase

requires evacuation of site done by blasting and crushing of the stones. Risk assessment is an important

step mandatory prior to any step taken for controlling pollution. Apart from this, safety precautions must be

taken during blasting. Measures, such as prior notification of the date and time of blasting to the workers,

have to be taken to consideration. Clearance of any workers present in the site before the time of blasting is

another safety precaution to avoid major accidents. Provisions, like ear muffs and ear plugs, have to be

supplied to the workers present in the site during the time of blasting and while using the crushers to crush

the stones.

Blasting also contributes towards air as well as noise pollution. Hence, hourly measurement of air quality

and noise equivalent noise levels has to be monitored during daytime and night times and compare it with

the standards as per National Ambient Air Quality Standards (NAAQS) as well as National Ambient Noise

Quality Standards (NANQS), as specified by the CPCB.

7.2.5.2 Construction Phase

While constructing the Pinjal dam, safety precautions have to be taken for handling the construction

materials by the workers. They should be provided with gloves while handling the paints and care should be

taken while carrying the materials made up of glass. This phase has a high risk for occupational hazards

and hence, mitigation measures have to be planned accordingly.

Transportation of construction materials and the process of construction of the dam lead to air pollution.

Pollutants like Particulate Matter (PM, SPM), NOx, CO2, CO and CH4 may be released. Any leakages of

fuels from vehicles may result in pollution of groundwater as well as soil. Dust emission from vehicles as

well as from raw materials like cement also contributes to air pollution. Necessary steps, such as regular

water spray to minimise fugitive emissions and baseline ambient air monitoring given by CPCB, have to be

taken to minimise the pollution generated during this phase.

The construction phase involves treating the effluents released from various sources such as worker

camps, crushers, etc., before being released into the main stream, thus requiring construction of settling

tank to precipitate suspended impurities. Treatment facilities have to be adopted for treating the sewage

thereby avoiding deterioration of water quality of the receiving water body. Solid waste disposal should be

planned in a way proving harmless to the environment.

Noise levels are to be checked and personal protective gears to be provided during periods of noise

exposure. Maintenance of equipment and machinery are to be checked regularly. Measures have to be

taken for the characterization and proper disposal of muck expected to be generated at various sites. A

first-aid box needs to be provided at the construction site.

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7.2.5.3 Operational Phase

Check on reservoir operation, surveillance, spraying of insecticide are few of the steps to be implemented

to control the water related diseases, likely to be prevalent in the Pinjal Dam site. Green Belt Development

is another step where action plans in identification of shrubs, ornamental plants and trees with respect to

elevation, water availability and type of soil, climate factor and local needs are to be done. This would inturn

result in the integration of landscape and restoration by creating green belt around the reservoir periphery

by nursery development, plantation, maintenance and completion of work. Delineating of staff for execution

of green belt development is also an important step. Soil erosion and siltation are to be taken care of with

check on embankments of dam, soil efficacy and necessary conservation steps should be taken. Also

changes in migration patterns of the aquatic fauna species have to be taken into consideration during the

operation phase. Management plan thus would involve catchment area treatment so as to avoid reservoir

sedimentation and also there would exist a requirement of constructing STP in order to treat the disposed

sewerage from the colonies.

A summary of the environmental management plan is given in Table 7.5.

Table 7.5: Environmental Management Plan

Environmental

Component Management Plan

Air Pollution During Construction

• Installation of dust extraction unit on the crusher to control the dust

generated during the crushing of stones at the preliminary stages

• Regular water spraying with water to be done over the stacked fine

aggregates thus preventing any fugitive emissions

• Baseline ambient air monitoring as per Central Pollution Control Board

(CPCB) norms

Water Pollution During Construction

• Treatment of effluent from sources like crushers, workers’ camps before

discharging to the main stream

• Construction of settling tank to settle the suspended impurities

During Operation

• Employing of suitable treatment facilities in order to treat the sewerage

generated from the colony thus avoiding deterioration of water quality of

the receiving water body

Noise Pollution During Construction

• Continuous exposure to the noise levels above 90 dB (A) has to be

avoided

• Personal protective gears such as ear plugs or ear muffs to be worn

during periods of noise exposure

• Regular maintenance of equipments and machineries

• Silencers and mufflers of the individual machinery to be regularly

checked

• Baseline ambient noise monitoring as per CPCB

Soil Erosion During Construction

• Selection of proper muck disposal site to avoid muck going into the river

• Adoption of soil erosion control measures i.e. engineering measures,

vegetative measures, reduction on use of fuel wood and management

measures

Terrestrial Ecology • Provision of grazing lands thereby reducing pressure on the forests

existing

• Mandatory afforestation to be employed

Aquatic Ecology • A minimum flow of during lean season should always be available in the

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Environmental

Component Management Plan

stretch between Dam and discharge point in order to maintain the aquatic

ecology

Road Construction:

Environmental

Management

During Construction

• The materials left in excess during the road construction are to be

collected and dumped in the designated muck disposal

• After disposal operation is completed at the dump site, dump yard has to

be vegetated and contoured

Muck Disposal Plan • After dumping the muck, disposal sites have to be restored

• Measures to be taken for the preservation of top soil layers

Pollution control from

the Workers’ Colony

• Legally compulsory provisions on various factors such as health,

sanitation and appropriate working conditions including accommodation

must be adhered to

• Solid waste management – facilities for collection, conveyance and safe

disposal of solid waste

Reservoir and River

Fish Management

During Operation

• Reservoir and river stretches downstream and upstream of the proposed

dam ought to be stocked with fingerlings

Mandatory

Afforestation &

Greenbelt

Development

• Consultation with the Forest Department, Thane District for necessary

action plan

7.3 Social Conditions

The submergence area corresponding to the proposed dam consists of 12 villages and 10 padas. They are:

Khidse, Ujjani, Vire, Manmohai, Manmowadi, Ene, Manmohai, Vadoli, Hedvali, Akhada, Bhagatwadi,

Barpachiwadi. Ongorichapada, Dhaknichapada, Kondichapada, Barpachiwada, Dakachapada,

Vadachapada, Dakchapada, Kukaronapada, Ujjanipada and Bhatipada. The submergence involves flora

and fauna in addition to affecting socially and economically backward people living in such areas. The

resettlement and rehabilitation (R&R) of the families have to be undertaken by the Government of

Maharashtra, ensuring the proper infrastructural facilities to the persons affected. Apart from the R&R, there

are other aspects to be included. They are:

During the pre-construction phase, land acquisition and other properties associated with it is an important

task to be undertaken. Employing local people for executing the Pinjal dam project is an essential step. The

Government of Maharashtra should assign adequate compensation to the dam-affected people, according

to the rehabilitation plan. The contractors taking up the project have to contribute towards local area

development by providing the local people with hospitals, schools, colleges, auditorium, etc.

Mitigation measures involve management of migrated population and protection of their rights, along with

capacity building of the local institutions for effectively handling additional responsibility for better

coordination and administration. Physical and mental health of the migrated population and the local host

community to be taken under consideration and should be serviced, thus providing effective health care

and counselling services. A summary of the social impacts of the Pinjal project and the ways they can be

tackled is presented in Table 7.6 and Table 7.7.

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Table 7.6: Social Impacts and Management

Table 7.7: Social Impact Mitigation and Monitoring Plans

Components Management Plan

Public Health During Construction and Operation

• A First- Aid post site to be allocated near the construction site

• Regular monitoring of water samples

Social Impact Mitigation • Site selection for construction of Dam and other infrastructural

facilities to be done facilitating the minimum acquisition of private land

• The capacity building of the local institutions for effectively handling

additional responsibilities must be taken up for better coordination and

administration

• Effective health care and counselling services to be provided at the

regular intervals for monitoring the physical and mental health of the

worker population as well for the local host community

Monitoring Plan

Public Health • Various health parameters including incidences of water born

diseases have to be monitored twice a year

7.4 Cost Estimation

Cost allocations for Environmental Management Plan and Social Assessment have to be planned for

allocation, since they may constitute a significant portion of the overall project cost. Such costs must also

include cost allocated to Environmental Monitoring Program, R&R studies, management measures and

other miscellaneous factors.

Parameters Anticipated

Impacts Management Measures

Pre construction phase

Socio-economic Acquisition of land as well as other properties; increase in the employment potential

Compensation as per the rehabilitation plan by the Government of Maharashtra

Construction phase

Socio-economic Increase in greater employment opportunities

Government would be providing certain percentage of power at free of cost; The company taking up the project would contribute towards development of infrastructural facilities like hospitals, schools, colleges, auditoriums etc

Operational phase

Socio-economic Migratory population handling

Protection of their rights along with capacity building of the local institutions for effectively handling the additional responsibility for better coordination and administration. Physical and mental health of the migrated population and the local host community to be taken under consideration for effective health care and counselling services

8-1 224604/ENI/IWU/1/0


Estimates of quantities of various items of civil works are based on preliminary layout drawings. Moreover,

costs of some items, such as signages, are not significant. For all such items, lump-sum provisions have

been made, based on judgement and provisions on other projects of similar nature. Thus, cost estimates of

the proposed Pinjal dam project are prepared, the details of which are given in this chapter. A few of the

unit rates, considered to arrive at the same, are given in Appendix C.1.

8.1 Civil Works

The estimated cost of civil works is based on both feasibility studies as well as preliminary planning and

designs carried out as per relevant IS codes for different components of works. These estimates, however,

do not involve environmental costs and social costs associated with the project.

A provision of 5—10% of the cost has been made to cover contingencies in the estimates of different

components of the civil works. Thus, the cost of Pinjal dam, without considering the proposed hydro-electric

power (HEP) house is INR 365.49 crores (see Appendix C.2.1). If the HEP plant is considered, then, the

resultant cost of Pinjal dam, including electro-mechanical works is INR 391.52 crores, the estimated cost of

HEP plant being INR 26.03 crores (see Appendix C.2.2).

Apart from these base costs, other items that add to the overall project cost are as given below:

8.1.1 I - Works

8.1.1.1 A—Preliminary Works

A provision of 2% of the cost of civil works has been made for preliminary items, such as topographic

surveys, geological and geophysical investigations, including drilling and drifting, environmental and

ecological studies, and consultants’ fees for preliminary as well as detailed engineering and design, and

preparation of project report.

8.1.1.2 B—Lands

This estimate includes acquisition and compensation charges of the land required for works and that

coming under submergence and for other properties like houses, wells, trees etc.

8.1.1.3 C—Works

This estimate includes the cost of civil engineering structures, including intake structures.

8.1.1.4 K—Buildings

Requirement of buildings for execution and subsequent running of the project is covered under this sub-

head. This includes provision for residential and non-residential buildings, both permanent and temporary.

This is done based on the expected size of the organisation at the site (excluding contractors’ labour), for

the actual execution of the project. It also takes into account the requirements for construction facilities to

be developed.

8 Cost Estimates

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8.1.1.5 M—Plantation

A provision has been made for planting trees, together with their maintenance and protection along the

project roads, colonies and important project components such as areas around the dam and powerhouse.

8.1.1.6 O—Miscellaneous

A provision of 3% of the cost of civil works has been made, in accordance with the government guidelines,

for the following major items.

• Capital cost of electrification, water supply, sewage disposal, drainage, etc.

• Maintenance and service charges during execution period

• Miscellaneous

8.1.1.7 P—Maintenance

A provision of 1% has been made of total cost of C--Works, K--Buildings and R--Communications. This

includes cost of maintenance of building approach roads and other structures during the project

construction period.

8.1.1.8 Q—Special Tools and Plant (Vehicles)

Provision has been made for vehicles such as cars, jeeps, buses and ambulances. Provision for

construction equipment has not been made under this head, as the construction of civil works will be

carried out by a separate agency.

8.1.1.9 R—Communications

Assessment of the total length of new roads, major bridges, requirements for improvement of existing

roads, strengthening of existing bridges and similar works has been made based on the site visit to project

areas.

8.1.1.10 X—Environment and Ecology

An estimated 1% has been made of the total cost of civil works for maintaining and improving the

environmental status of the project area.

8.1.1.11 Y—Losses on Stock

A provision of 0.25% of I - Works less A—Preliminary, B—Land, and Q—Special T&P has been made.

8.1.2 II - Establishment

A provision of 8% of I - Works less B—Land has been allowed for establishment costs.

8.1.3 III - Tools and Plant

An allowance of 1% of I - Works has been made for survey instruments, office equipment and other small

tools and plant.

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8.1.4 V - Receipt and Recoveries on Capital Account

Total recoveries on account of temporary buildings and Q—Special T&P (Vehicles), by way of resale or

transfer, are considered.

8.1.5 Indirect charges - Audit and accounts

A provision of 1% of the cost of I - Works for audit and accounts charges has been considered.

8.2 Estimated Cost of the Project

Overall cost, including land, buildings, environment & ecology, tools, transportation and other

miscellaneous costs is INR 1,134.38 crores.

The abstract sheet, describing various costs, is included in Appendix C.2.3.

I 224604/ENI/IWU/1/0


Appendix A. Data _____________________________________________________________________________ II Appendix B. Design____________________________________________________________________________III Appendix C. Cost Estimates _____________________________________________________________________ V Appendix D. Drawings_________________________________________________________________________ VI

Appendices

II 224604/ENI/IWU/1/0


A.1. Observed Monthly Rainfall

A.2. Observed Monthly & Annual Runoff at Andhari G&D Site

A.3. Consistency Checks of Data

A.3.1. Rainfall

A.3.2. Runoff

A.4. Pan Evaporation Depths

A.5. PMP Data (IMD)

A.6. Silting of Reservoirs in India

A.7. Geotechnical Engineering Report

Appendix A. Data

III 224604/ENI/IWU/1/0


B.1. Derivation of Missing Rainfall Data

B.2. Weighted Monsoon Rainfall

B.3. Rainfall-Runoff Model

B.4. Yield Series & Dependable Yield

B.4.1. Andhari G&D Site

B.4.2. Pinjal Dam Site

B.5. Synthetic Unit Hydrograph

B.6. Design Flood

B.6.1. Temporal Distribution of Rainfall

B.6.2. Design Storm (IMD)

B.6.3. Design Flood (IMD)

B.6.4. Design Storm (CWC)

B.6.5. Design Flood (CWC)

B.6.6. CWC Recommendations

B.7. Sedimentation Analysis

B.7.1. Trap Efficiency

B.7.2. Sediment Distribution at 17.9 Ha-m/100sq.km/year for 100 years




B.8. Monthly Inflow Series for Reservoir Simulation

B.9. Reservoir Simulation Studies

B.10. Free Board

Appendix B. Design

IV 224604/ENI/IWU/1/0


B.11. Head Loss for Hydropower Generation

B.12. Hydropower Generation

B.13. Diversion Tunnel

B.14. Design of Ogee Spillway and Energy Dissipation Arrangements

B.15. Stability Analysis of Overflow Section

B.16. Stability Analysis of Non-Overflow Section – Main Gorge

B.17. Stability Analysis of Non-Overflow Section – Shallow Gorge

B.18. Summary of Stability Analysis

V 224604/ENI/IWU/1/0


C.1. Rate Analysis: Unit Rates

C.2. Cost Estimates

C.2.1. Civil Works

C.2.2. Hydroelectric Power Plant

C.2.3. Abstract of Project Cost

Appendix C. Cost Estimates

VI 224604/ENI/IWU/1/0


D.1. MMD-224604-C-DR-PIN-XX-0001 INDEX MAP OF PINJAL DAM

D.2. MMD-224604-C-DR-PIN-XX-0002 ALTERNATIVE LOCATIONS OF PINJAL DAM AND SUBMERGENCE

D.3. MMD-224604-C-DR-PIN-XX-0003 LAND USE PATTERN AT THE LOCATION OF PINJAL DAM

D.4. MMD-224604-C-DR-PIN-XX-0004 THIESSEN POLYGON NETWORK SHOWING RAIN GAUGES & GAUGE DISCHARGE

STATIONS FOR PINJAL CATCHMENT

D.5. MMD-224604-C-DR-PIN-XX-0005 SURVEYED CROSS SECTION WITH BORE HOLE DETAILS FOR PINJAL DAM LOCATION

D.6. MMD-224604-C-DR-PIN-XX-0006 AREA CAPACITY CURVE

D.7. MMD-224604-C-DR-PIN-XX-0007 GENERAL LAYOUT OF PINJAL DAM AND APPURTENANT WORKS

D.8. MMD-224604-C-DR-PIN-XX-0008 PLAN AND ELEVATION OF PINJAL RIVER SHOWING OVERFLOW AND NON OVERFLOW

DETAILS

D.9. MMD-224604-C-DR-PIN-XX-0009 CROSS-SECTION OF OVERFLOW (OGEE SPILLWAY) SECTION AT CH. 595.00 M

D.10. MMD-224604-C-DR-PIN-XX-0010 CROSS-SECTION OF NON-OVERFLOW SECTION AT CH. 432.00 M

D.11. MMD-224604-C-DR-PIN-XX-0011 CROSS-SECTION OF NON-OVERFLOW SECTION AT CH. 1800.00 M IN SMALL GORGE

D.12. MMD-224604-C-DR-PIN-XX-0012 CROSS-SECTION OF NON-OVERFLOW SECTION WITH PENSTOCK ARRANGEMENT FOR

POWERHOUSE AT CH. 255.00 M

D.13. MMD-224604-C-DR-PIN-XX-0013 PLAN AND CROSS-SECTION OF POWERHOUSE

Appendix D. Drawings

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