1. Metro Colombo Urban Project - World...

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1. Metro Colombo Urban Development Project

Environmental Screening Report for 1. Improvements to Mutwal Outfall (box drain, tunnel inlet and outlet) 2. Reconstruction of Aluth Mawatha culvert 3. Embankment protection along selected locations of the Main Drain

Final Report

December 2011

Uni‐Consultancy Services University of Moratuwa

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E2886 v7

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Table of Contents

1. Project Identification 3

2. Project Location 3

3. Project Justification 5

4. Project Description 8

5. Description of the Existing Environment 11

6. Public Consultation 19

7. Environmental Effects and Mitigation Measures

7a. Screening for Potential Environmental Impacts 21

7b. Environmental Management Plan 29

8. Conclusion and Screening Decision 51

9. Screening Decision Recommendation 65

10. EMP implementation responsibilities and costs 66

11. Details of Persons Responsible for the Environmental Screening 69

Annexes

1. Photographs of some of the important locations along project roads

2. Detailed drawings of project components

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Metro Colombo Urban Development Project

Environmental Screening Report

1. Project Identification

Project title 1. Improvements to Mutwal Outfall (box drain, tunnel inlet and outlet) 2. Reconstruction of Aluth Mawatha culvert 3. Embankment protection along selected locations of the Main Drain

Project Proponent

Sri Lanka Land Reclamation and Development Corporation

2. Project Location

Location Location of the project is depicted in the Fig. 1.

Definition of Project Area

(The geographical extent of the project & areas affected during construction)

The project area is the (i) culvert across Aluth Mawatha, (ii) the canal banks of the Main Drain from St. Sebastian North Canal through Prince of Wales Avenue and to Port Access Road up to the culvert at Aluth Mawatha, (iii) Mutwal tunnel and the outfall

The geographical extent is shown in Fig. 1.

Adjacent land and features

See “Other features” in Section 5.

URBAN UPGRADING WORK

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Figure 1. Location map showing the Main Drain and the Mutwal Tunnel Outlet

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3. Project Justification

Need for the project

(What problem is the project going to solve)

The Colombo Drainage System comprises a network of large open drainage canals, smaller tributary canals and low-lying marshes functioning as natural retention basins. It functions to serve the drainage needs of the Greater Colombo area and reduces incidence of flooding and thereby protects the urban community, particularly the urban poor who inhabit low-lying regions of Colombo.

The system could be broadly divided into two, with canals to the north of Sri Jayawardenepura Mawatha as Colombo North system and that to the south as the Colombo South system (see Figure 1. The system has four outlets and three of which Dehiwala and Wellawatte Outfalls and Mutwal Tunnel directly discharging in to the sea, while the North Lock discharges in to the Kelani River. There is a fifth outlet for the spill waters of the Beira Lake, via a circular weir near the old Parliament; the canal system is no longer connected to the lake to prevent highly polluted canal waters entering the lake. When the Kelani River level is high, the gate at the North Lock outlet to Kelani River is closed, so that reverse flow (from the river into the system) cannot take place. This operation is now carried out by the Department of Irrigation. Mutwal Tunnel of diameter 1.8 meters, functions as the outlet of the Main Drain.

The head of the canal system could be considered as Parliament Lake, to the East of Kotte Lake. Under dry weather conditions the North Lock, Wellawatte and Dehiwala outfalls are the major outflow points. In a flood situation, with the North Lock closed due to high water level in the Kelani River, the system has to rely mainly Wellawatte and Dehiwala sea outlets. Also the Mutwal Tunnel helps ease the drainage problems of North Colombo to a great deal at times when the North Lock is closed.

Aluth Mawatha Canal, Mutwal Tunnel and Outfall

The Main Drain takes off the flow from St. Sebastian North Canal through a culvert crossing Prince of Wales Avenue and it runs mostly parallel to the Port Access Road and crosses the canal at two locations.

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Then the canal changes its direction to the North and enters Aluth Mawatha area by crossing the Railway Track to the Colombo Port. At Aluth Mawatha the Main Drain connects to the Mutwal Tunnel through Aluth Mawatha Culvert (of which the existing capacity is not adequate) followed by a box drain (3 m x 3 m; L = 82 m). There is an urgent need to increase the capacity of this culvert.

Mutwal Tunnel is approximately 1.8 m diameter horse shoe type tunnel of which the length is 570 m. The Mutwal Tunnel outlet is the only outlet that discharges storm water from the Colombo North area canal system directly into the sea.

The inlet to the tunnel is at a dilapidated state at the moment that needs urgent rehabilitation.

Thus the enhancement of the conveyance capacity of the Mutwal Outfall is essential and accordingly rehabilitation & upgrading of the system is required.

Purpose of the project

(what is going to be achieved by carrying out the project)

The purpose of the project is to:

- Increase the capacity of the culvert across Aluth Mawatha

- Accommodate improvements to Mutwal Outfall (box drain, tunnel inlet and outlet)

- Embankment protection along selected locations of the Main Drain

The purpose of the project is to derive the following benefits and the beneficiaries are listed below:

Benefits

∗ Enhancement of flood control. ∗ Reduction in allocations for flood relief for the Government. ∗ Increased in land values in adjacent areas. ∗ Improved health conditions & reduction in health

expenditure. ∗ Reduction in annual operation & maintenance cost to the

central government. ∗ Increased use of the canal system for recreational purposes

& waterfront development.

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Beneficiaries

∗ People residing close to the Main Drain and with the combined effect, the entire Colombo Metropolitan area.

∗ The Government and the agencies managing the storm water drainage.

Alternatives considered

(different ways to meet the project need and achieve the project purpose)

No other alternative is considered for the project as it is envisaged that there are no any technically feasible and economically viable engineering interventions that could be accommodated in place of the proposed option.

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4. Project Description

Proposed start date

The tender documents are expected to be ready by December 2011. Awarding of the tender will take place only after the 16th of March 2011. Construction period is estimated to be one year.

Proposed completion date

It will take minimum 12 – 15 months to finish the project from the date of opening bid documents.

Estimated total cost

Estimate: 3.34 US$ million

Present land ownership

Entire project lies in areas belonging to SLLRDC.

Description of the project

(with supporting material such as maps, drawings etc attached as required)

The detailed drawings of the project are given in Annex 2.

List of Proposed Activities 1. * Rehabilitation of Main Drain Bank Protection

New Gabion walls - 1450 m

New sheet pile walls - 57 m

Rehabilitation of gabion walls - 778 m

{Total length of Main Drain = 1650 m}

∗ Reinstatement of storm water drainage connections (hume pipe) to Main Drain through gabion walls and introducing catch-pits wherever required.

2. Aluth Mawatha Culvert Improvement

∗ Demolish and reconstruct 3.0 x 3.5 x 12 m reinforced concrete box culvert

∗ Connection of box culvert to existing 3.0 x 3.0 mm box drain leading to Mutwal Tunnel.

∗ Reinstatement of Aluth Mawatha at culvert locations ∗ Temporary shifting & relocation of service lines (electricity, water,

telecom, sewer) 3. Renovation of existing box drain (covers of the openings - 6 Nos.)

connecting Aluth Mawatha culvert & Mutwal Tunnel and anticipated catch-pits carrying storm water.

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4. Replacement of covers of Mutwal Tunnel manholes (03 Nos.) a). Stream lining of inlet area to suit the transition

∗ Introducing a trash screen

∗ Formation of 2 Nos. new storm water manholes at Mutwal inlet and connection of the above two to inlet areas.

∗ Construction of boundary fence around the inlet areas a (with a gate) as a safety measures.

5. Stream lining the Mutwal Outfall

In addition to the above, operation and maintenance of the drainage system is needed. The main drain, Mutwal box drain, & tunnel are under the custody of SLLRDC. Hence it will be maintained by Colombo North Regional Office; Drainage Division of SLLRDC. Following are the activities done under regular maintenance.

a). Regular observations

b). Surface clearing

c). Canal dredging

d). De-silting of box drain, tunnel & catch-pits.

Project Management Team

Agency:

The agency responsible for design and implementation is the SLLRDC and the organization structure for the project is given in Figure 2

Contact person: Ms. A.H. Thushari

Assistant General Manager (Special Projects) Sri Lanka Land Reclamation & Development Corporation

Nature of the consultation and input received:

Meeting and consultation at design office and site were done. Design drawings, master plans and other relevant information were too gathered.

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Figure 2. Implementation arrangements for MCUDP under SLLRDC

PROJECT MANAGER

DEPUTY PROJECT MANAGER

Consultant Engineer (Contracts & Claims)

Planning Engineer

Design Engineer

Accountant

Quantity Surveyors

Draughtsmen

AO/Clerk

Computer Operators

Office Aide

Driver

Consultant (Land Acquiring)

Land Officer

Project Engineer

(B)

Project super‐visor

Project Engineer

(A)




Environmentalist

Social Planner

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5. Description of the existing environment

5.1 Physical features – Ecosystem components

Topography and terrain

The topography of Sri Lanka is marked by great diversity caused by long years of faulting and erosion of the landscape. The central mountainous region with the highest elevations covered by virgin forests and grasslands rises up to about 2,500 m above mean sea level. The surrounding plains, which rise to about 50 to 100 m above sea level, are largely used for agriculture and homesteads, but still have virgin scrubland where the population distribution is lower. This general topography of the country can be divided into three distinct geographical areas or well marked peneplains featuring the coastal belt, the plains, and the central highlands. The Colombo district which incorporates the project area falls into the so called lowest peneplain of Sri Lanka (after P.G. Cooray – Geology of Sri Lanka, 1984). The elevation variation of Colombo district situated in this coastal peneplain ranges to a maximum elevation of 150 m from sea coast. The terrain in Colombo largely consists of gently undulating plains and low-lying flatlands with a high density of drainage paths formulating a geography consisting of a mix of land and water. The city has many canals and the 65-hectare (160-acre) Beira Lake situated in the heart of the city is one of the most distinctive landmarks of Colombo. Mutwal is part of the Colombo Core Area and lies about 3 km north-east to the Colombo commercial hub. The Mutwal sea outfall which has a 5 m3/s capacity is one of the five outlets of Colombo drainage system and it drains the low-lying catchment and accumulated runoff in the connected drainage canals directly to the sea through 6 feet diameter tunnel constructed through underlying rock. The general topography of the project area in Mutwal and Aluth Mawatha where drainage improvement, embankment rehabilitation and culvert expansion works have been proposed consists of largely flat or mildly sloping low-lying terrain. Elevations vary only from 0 m MSL (at sea level) to 6

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m MSL in high areas. Therefore, the slopes encountered in the project area are flat to mild (<0.8 %) and gently slope in seaward direction while the contour lines are aligned approximately parallel to the shoreline.

Soil (type and quality)

The geology of Colombo is representative of the geology of the western coast of Sri Lanka and has existed for much of the Quaternary era. Bore holes drilled in central Colombo City show that this area once formed an estuary of the Kelani River and the Kalu Ganga River, the two main rivers that drain into the sea on the western coast. A few kilometers upstream in the inland valleys, there is a high-level gravel formation consisting of quartz pebbles embedded in a matrix of laterite separated with pebble-free layers of laterite. The floodplains along the rivers consist mainly of alluvial deposits. The floodplains of Kelani River also provide thick alluvial profiles for unconfined aquifers, in addition to the productive overburden along tributary banks. Vast area (over 90%) of Sri Lanka is underlain by metamorphic crystalline rocks of Precambrian age, which includes the project area, which cover a variety of Gneisses. The geology of Colombo is representative of the geology of the western coast of Sri Lanka and has existed for much of the Quaternary era. This is shown in the 1:10,000 and 1:50,000 geological maps of Colombo region produced by the Geological Survey and Mines Bureau. The typical rock types of this basement include Biotite gneiss, Hornblende Biotite gneiss, Charnockites, Charnockitic gneisses, Quartzite and undifferentiated Meta sediments. The floodplains along Kelani River and the Kalu Ganga rivers consist mainly of alluvial deposits. The floodplains of Kelani River also provide thick alluvial profiles for unconfined aquifers, in addition to the productive overburden along tributary banks. According to Survey Department soil maps (Figure 3) the main soil types in the project area are as follows.

• Red Yellow Podzolic soils with soft or hard laterite and undulating terrain • Bog and Half bog soils: flat terrain • Alluvial soils of variable texture and drainage: flat terrain • Regosols on recent beach sands: flat terrain

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Field surveys and observations carried out using trial pit holes have indicated that the local geology in the proposed project area is characterized by organic clays with sand and deep bedrock while the soil types include peaty and sandy clays with clayey laterite types sporadically distributed in patches. It is presumed that these site-specific features are the most important ones as the environmental impact is considered.

Figure 3. Soil Maps of the Study Area (Source: Greentech)

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Surface water (sources, distance from the site, local uses and quality)

Sources

The most prominent source of surface water in the vicinity is the Main Drain and the surface water drainage canal network that is connected to it.

Distance from the site

Project area includes the Main Drain, Aluth Mawatha culvert, banks of the canal and Mutwal tunnel and the outfall.

Local uses

The canal plays an important role in conveying surface drainage and flood waters. Although the local people do not derive other benefits than diverting their surface drainage into these canals, the intrinsic function is vital and most important in draining the flood waters of the area. There are numerous illegal discharge points of grey water from residences, commercial establishments and warehouses located adjoining the canal, and due to appalling level of water pollution, no other local uses can be derived from the water body.

Quality

Recently measured data is not available for water quality of the Main Drain.

It is visible that the turbidity and total suspended solid content are very high in the water. It is highly likely that dissolved oxygen, and pH are too not in the range that is amenable for biological activities but conducive for anoxic conditions to prevail mainly due to the lack of dissolved oxygen. Nutrient enrichment is apparent in the canal due to disposal of domestic and industrial wastewater and solid waste into the canal over time.

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Ground water (sources, distance from the site, local uses and quality)

Sources

According to the Land Use Division of the Irrigation Department, the project area falls within the local or discontinuous moderate to low aquifer in fractured rock. Only available source of ground water is abstracting water from shallow wells. Distance from the site

The ground water table is very shallow and is about 0.5 m on average close to the Canal, and can be at a level from almost at surface up to 2.0-3.0 m.

Local uses

Only a handful of households use shallow wells to abstract water. Even those who have shallow wells do not use water for daily consumption; they use the wells only occasionally for bathing and washing of clothes.

Quality

There are no data available for quality of ground water. However, it can be assumed that dissolved solid levels including salinity to be high as the project area is located very close to the coastal belt. The ground water can get contaminated due to dilapidated state of sewer connections due to leakages.

Flooding The downstream areas in Mutwal, especially the area surrounding Aluth Mawatha Road, has suffered from intermittent flooding in the recent past presumably. This is mainly due to unfavorable downstream conditions caused by inadequate capacity of the culvert at Aluth Mawatha that does not facilitate additional flow as a result of elevated flood levels and in part due to temporary blockage of existing storm water drainage system by debris, solid waste disposal and siltation. Recorded flood levels in Aluth Mawatha Road and adjacent localities are in the range of 0.3 ~ 0.6 m during monsoon months.

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Air quality (any pollution issues)

Heavy vehicle movements along Aluth Mawatha in the project area lead to high levels of air pollutant emissions, such as dust including particulate matter, smoke including CO, CO2, NOx, SOx etc. Such air pollution episodes can aggravate during peak hours when traffic movements are impeded. Construction sites in the vicinity and within the project area affect the air quality in the area immediately surrounding such construction activity. Fugitive dust particles could escape into the atmosphere during such construction activities and during transportation and subsequent storage and handling. Emanation of foul odors from the canal, especially during dry weather when water levels are low, could take place from rotting solid wastes thrown in the water and sewage discharges.

Noise level and vibration (Any anticipated issues)

Existing ambient noise and vibration levels in the area are consistent with highly urban and light industrial and businesses. There is also heavy traffic noise from major roads such as Aluth Mawatha, St. Andrew’s Road and Elli House Road. Intermittent high levels of noise and vibration levels are observed due to train operations of Petroleum Corporation. Industrial activities and commercial activities of most of the major roads mentioned above contribute to high levels of noise. Noise and vibration levels in the area would increase slightly due to the proposed construction activities.

5.2 Ecological features – Eco-system components

Vegetation

(trees, ground cover, aquatic vegetation)

Main Canal, Aluth Mawatha

The canal embankment is highly affected by human interventions. Therefore, no trees can be found along the canal stretch from the railway line to the Aluth Mawatha Canal. Some trees were recorded upstream of the railway line and within the vicinity of the project area viz, Terminalia catappa (Kottan), Ficus religiosa (Bo), Cocus nusifera (Pol), Mangifera indica (Amba).

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Culvert

There is a Bo tree (Ficus religiosa) located on top of the culvert and its roots have penetrated through the canal and the culvert.

Mutwal outfall

The outfall is area also dominated by man-made activities including settlements, commercial establishments and industrial activities and no trees were found. However, ground cover of Bim thambaru (Ipomoea asarifolia) and Elephant's ear (Colocasia esculenta) were found near the sea outfall.

Presence of wetlands There are no wetlands found within and vicinity of the project area.

Fish and fish habitats

Fish sampling was not carried out. However, schools of small fish can be found plenty in the canal.

Birds (waterfowl, migratory birds, others)

Other than the common birds observed during the rapid screening survey such as Saxicoloides fulicata (Indian Robin), Copsychus saularis (Oriental Magpie Robin), Acridotheres tristis (Common Mayna), Streptopelia chinensis (Spotted Dove), Pelecanus philippensis (Spot Billed Pelicon), Ardeola grayii (Indian Pond Heron) no endemic or threatened animal species were recorded.

Presence of special habitat areas (special designations & identified sensitive zones)

There are no such special habitats demarcated as protected areas within and immediate surroundings of the project area.

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Other features

Residential/Sensitive Areas (Eg, Hospitals, Schools)

Throughout the study area on either side of the canal is occupied by underserved settlements. No sensitive land uses such as schools, hospitals were recorded. The Mutwal tunnel outlet traverses the Colombo Fishery Harbour Corporation before it discharges to the sea.

Traditional economic and cultural activities

Most of the households of the area are involved in informal sector activities.

No traditional economic or cultural activities recorded.

Archeological resources

No Archeological resources are located in the project area.

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6. Public Consultation

Public consulted Consultation method

Date Details/Issues raised

Mr. Ramkumar (Left Bank near the culvert) Mr. Siriniwasan (Left Bank near the culvert) Ms. Pilamina (President / Community Leader of the right bank)

Mr. Sinnathambi (On the tunnel trace)

Mr. Perera (On the tunnel trace)

Informal Interviews

19.12.2011

Before the widening of the canal, they had a good access to the canal bank, but after the widening, the access road gradually eroded. During the proposed improvements it is necessary to provide access to these premises. (Only one house) The community on the left bank had got access from a road on the rear boundary and that was closed by the owner and therefore the canal bank is the only access they have. It is important to make the canal bank road available for these two families. Construction of the gabion wall is a good option as it will prevent encroachments. After previous improvements, the area did not go under water. The cover slabs of the tunnel are broken at many places creating a big danger for children who play on this trace.

The canal trace (the covered section) is the access road to this settlement. Children play on this trace and always there is a danger due to collapse of cover slab. If the project can upgrade this stretch as a good access road the community will benefit

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Sashi Kumar (Resident of Aluth Mawatha and Three Wheeler Driver)

M.H Wilfrida, Mary Isabel, Ajith Kumar (residents of 321 Garden –along the Mutuwal box drain trace linking with the tunnel inlet

09.12.2011

09.12.2011

largely.

The project is a positive initiative. However, the traffic situation during the construction of the culvert need to be planned properly as this road is heavily used by containers and trucks headed for the port.

It is expected that the project will ease the flood risk in the area and reduce water stagnation. Temporary cutting off access to the Garden is not a major issue when the box drain is open for rehabilitation as there are two main alternative routes.

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7. Environmental Effects and Mitigation Measures

7a. Screening for Potential Environmental Impacts

Screening question Yes No Significance of the effect

(Low, moderate, high)

Remarks

1 Will construction and operation of the Project involve actions which will cause physical changes in the locality

Yes Low

Most of the interventions are carried out along the canal hence no physical changes in topography and landform is anticipated other than strengthening of the canal banks with gabion structures, landscaping, paving of foot walks and road surfaces.

2 Will the Project involve use, storage, transport, handling or production of substances or materials which could be harmful to human health or the environment or raise concerns about actual or perceived risks to human health?

Yes Low

Transport of material and construction activities, including excavation, demolition of the existing culvert and material piles will emit dust and fugitive particles which may pose a health hazard to vulnerable persons in the immediate surrounding on temporary basis. The wind will be the triggering factor for such impacts though it is sporadic in nature.

3 Will the Project produce solid wastes during construction or operation?

Yes Moderate

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During construction:

There will be small amounts of construction debris produced during demolition of existing culvert across the road, structures and pavements, excavation of trenches.

During operations:

There will be street sweepings, solid waste collected at garbage bins and dump areas which need regular collection and disposed appropriately. In addition, debris and sediments, floating matter and other solid waste carried by surface drainage which can collect at manholes, catch pits etc. that needs proper disposal. Regular cleaning of side drains and road will too generate such material. Culverts will also generate spoil material.

4 Will the Project release pollutants or any hazardous, toxic or noxious substances to air?

Yes Low

There will be bituminous material used during overlay and re-surfacing of Aluth Mawatha, bituminous patching, crack sealing, carriageway edges and shoulder repairs.

5 Will the Project cause noise and vibration or release of light, heat energy or

Yes Low

The project activities will cause noise and vibration

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electromagnetic radiation?

during demolition of the existing culvert, asphalt overlay, excavation of trenches, and during compaction, construction of gabion walls, transport of material etc. These impacts are temporary in nature and will cause inconvenience to the neighboring people only.

6 Will the Project lead to risks of contamination of land or water from releases of pollutants onto the ground or into surface waters, groundwater or coastal wasters?

Yes Low

The canal where the base of the gabions will be placed will need to be excavated to remove the soft surface sediment layer. Such excavated material should be disposed of safely. Stock piling of excavated sediment material, soil, debris and other material may release pollutants back into surface waters, groundwater or coastal waters. If the excavated bottom sediment is contaminated with heavy metals, and if those removed materials are not properly handled and disposed, they might pose a significant environmental and health risks to the residents and downstream marine ecosystems.

7 Will the project cause localized flooding and poor drainage during construction

Is the project area located in a flooding location?

Low

Temporarily blocking of existing drainage flows may be required during constructional activities for the proposed tunnel improvement works in Mutwal, culvert and bank restoration/ rehabilitation works

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along the Main Drain leading to localized flooding. Raised embankments and raised finish levels, stock piling of construction debris and other materials may block existing drainage flow paths, causing flow stagnation and poor drainage leading to temporarily flooding effects.

Aluth Mawatha Road in the proposed project area is an identified flood prone area and the ensuring of proper construction practices like provision of improved drainage network, maintaining naturally stable slopes, vegetation replanting/turfing, etc. will improve drainage conditions, reducing flood risk during the construction phase and in the aftermath of project completion. Additional pumping and dewatering should be arranged during the construction phase, if the alternative flow diversions provided are not adequate.

8 Will there be any risks and vulnerabilities to public safety due to physical hazards during construction or operation of the Project?

Yes Low

Excavation for Gabion wall construction may cause the adjoining properties to collapse causing destruction to accessibility. (Particularly the family staying close to the culvert)

Safety issue in terms of injuries caused by construction material, machinery and falling into

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excavated trenches by neighbors and commuters could be anticipated.

9 Are there any transport routes on or around the location which are susceptible to congestion or which cause environmental problems, which could be affected by the project?

Yes Low

Due to the closure of Aluth Mawatha for construction of the culvert and asphalt overlay, traffic would be diverted through the main Mattakuliya road which by-passes Aluth Mawatha but connect the same destinations. It is likely that Aluth Mawatha can be operated for one-way traffic while the construction of the culvert is in progress. The traffic on the Mattakuliya road will be increased as Aluth Mawatha is used by traffic headed to the port. However, this will be a temporary impact.

10 Are there any routes or facilities on or around the location which are used by the public for access to recreation or other facilities, which could be affected by the project?

Yes No Low

There are no significant recreational, or similar facilities located on or around the project area.

11 Are there any areas or features of high landscape or scenic value on or around the location which could be affected by the project?

No Since project mainly deals with work along the canal and roads, no impact is anticipated.

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12 Are there any other areas on or around the location which are important or sensitive for reasons of their ecology e.g. wetlands, watercourses or other water bodies, the coastal zone, mountains, forests which could be affected by the project?

Yes Low

No such sensitive areas are found in the project area other than the coastal area.

13 Are there any areas on or around the location which are used by protected, important or sensitive species of fauna or flora e.g. for breeding, nesting, foraging, resting, migration, which could be affected by the project?

No No such areas are found.

14 Is the project located in a previously undeveloped area where there will be loss of green-field land

No The project area and the surrounding is fully developed and one of the high density residential areas in the city of Colombo.

15 Will the project cause the removal of trees in the locality?

Yes There is a Bo tree (Ficus religiosa) which has grown on the culvert that has to be removed during construction.

16 Are there any areas or features of historic or cultural importance on or around the location which could be affected by the project?

No There are no cultural/religious places which are located along the roads which are affected during construction.

17 Are there existing land uses on or around the location e.g. homes, gardens, other

Yes Low

The land use of either side of the project area is

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private property, industry, commerce, recreation, public open space, community facilities, agriculture, forestry, tourism, mining or quarrying which could be affected by the project?

dominated by high density residential development (underserved settlements). A few retail commercial establishments are found on Aluth Mawatha road. From the Aluth Mawatha culvert towards the railway a few industries and stores are located on the left bank area. At the Mutwal out fall a large extent of land is covered by the Fisheries Department fishery facility and flour milling industry. However impacts of the project on these land uses are negligible as the construction activities of the project are limited to a very narrow strip that will not have any connection with the aforementioned land uses.

18 Are there any areas on or around the location which are densely populated or built-up, which could be affected by the project?

Yes Low

The adjacent areas of the project are heavily built up as this is an area of concentration of underserved settlements. The impacts would be mostly disturbance to pedestrian movement which is of short duration nature.

19 Are there any areas on or around the location which are occupied by sensitive land uses e.g. hospitals, schools, places of worship, community facilities, which could be affected by the project

No No such sensitive areas are found.

20 Are there any areas on or around the No The fisheries development facility of the Fisheries

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location which contain important, high quality or scarce resources e.g. groundwater, surface waters, forestry, agriculture, fisheries, tourism, minerals, which could be affected by the project?

Department is located at the Mutwal canal out fall. However there is no fishing activities carried out at this location. Its main functions are collection of fish that are brought by boats and distribution by lorries. Thus there is no impact by the project.

21 Are there any areas on or around the location which are already subject to pollution or environmental damage e.g. where existing legal environmental standards are exceeded, which could be affected by the project?

Yes Aluth Mawatha canal is highly or moderately polluted depending on the seasonal effects. There is a continuous leak from petroleum pipelines causing oil pollution close to the railway track.

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7b. Environmental Management Plan

Key project activities Potential Environmental Effects

Mitigation Measures

Site preparation including provision of access roads, material storage yards

Physical:

Emission of dust

Social:

Disturbance to pedestrian movement, accessibility to houses.

Ecological:

No impact

Physical:

Clearing of the canal bank for on-site material storage and access has to be carried out with the minimum use of machinery and sprinkling of water should be done appropriately.

Social:

One house on the left bank near Aluth Mawatha culvert is the most affected as its current access is very narrow located on the canal bank. This access road should be incorporated into the canal reservation so that it can be used as a good access road also.

Ecological:

N/A

Temporary shifting & relocating of utility posts (electricity, water, sewer & telecom).

(This is only for re-construction of Culvert across Aluth Mawatha

Physical:

No impact

Social:

Physical:

N/A

Social:

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Mitigation Measures

Road)

Disturbance to pedestrian and vehicular movement.

Ecological:

No impact

Provide adequate de-routing facilities and keep the pedestrians and drivers well informed by fixing sign boards on appropriate locations.

Ecological:

N/A

Canal bank/bottom excavation, dewatering and disposal of bottom sediments

Physical:

Excavations of the canal banks and the canal bed where the base of the gabions will be placed will be needed during proposed construction activities to provide the base layer for embankment and gabion wall construction/ rehabilitation and for maintaining the required design depths in the existing canals. These activities would degrade water quality by mixing of fines and potentially contaminated

Physical:

Sediment quality in the proposed sections of the Main Drain should be established to understand the risk of contamination involved and to determine the suitable disposal method for the excavated sediments and waste. If contamination is established according to accepted reference criteria, disposal must be planned properly, as indicated below.

(a) given the small volume of exvated sediments that will be generated from this stretch of the canal (300m) the project should explore the possibility of using the two existing (and only) small semi engineered landfills in Sri Lanka at Mawanella ad Nuwara Eliya. Since the anticipated volume of excavated matter in this case would be small, the project would be able to negotiate with the Central Environmental Authority and the relevant Pradheshiya Sabhas for using their facility or (c) dispose to Holcim industrial incinerator as alternative fuel.

31


Mitigation Measures

material into downstream areas of the canal and ground water. Dewatering may cause surface ponding of removed water if proper drainage is not allowed, especially when the upper soil layers are saturated due to recent storm events. Excessive dewatering may cause water table to decline rapidly, lowering soil pore pressure and sinking and localized land subsidence effects adjacent to existing load bearing structures.

Stock piling of excavated material, soil, debris and other material may block surface drainage paths causing localized flooding during constructional and operational periods.

There will, however, be a cost involved in incinerating the material at Holcim which is presumably not significant given the small quantities.

Proper and adequate dewatering should be ensured either using a proper monitoring schedule or using an automated submersible pump system with float device to ensure site activities are uninterrupted due to seepage water.

Proper surface drainage and retention-detention capacity should be provided to safely remove pumped-up water from the site to a natural drainage to avoid in site ponding effects.

Construction activities can be planned during the periods of low water table to avoid excessive dewatering requirements and save costs while reducing risks of slope failures, increased erosion, etc.

The construction materials intended for temporarily storage should be properly stockpiled in most appropriate areas in the site to avoid disturbance to site mobility, traffic and stored away from drainage paths and suitably covered to avoid washout.

Silt traps and catch pits should be used during construction period where necessary to avoid excessive mixing of fines and

32


Mitigation Measures

Social:

Odour problems

Ecological:

Smothering of benthic fauna

potentially contaminated material back into canal and downstream water bodies. All collected fines, excavated materials should be properly stored until safe disposal at suitably selected, adequately isolated disposal grounds.

Social:

Odour of this nature is of very short term duration and thus is negligible. However if excavated material causes odour to emanate, removal of such material as practical as possible would be undertaken. The handling of such material must be done only after the sediment quality testing has been carried out and according to its conclusions.

Ecological:

Depending on the disturbance of the first few cm of the benthic layer, fauna that inhabit the top layer could be temporary disturbed. Hence disturbance must be made to the minimum level so that they could once again establish soon.

Removal of temporary structures, debris, demolition waste and other

Physical: Physical:

The demolished materials and debris intended for temporarily

33


Mitigation Measures

solid waste along the banks

Emission of dust and noise

Disturbances to traffic and pedestrians during storage of material and debris.

Social:

Inconvenience to present residents and pedestrians.

Ecological:

No impact

storage should be properly stockpiled in most appropriate areas in the site to avoid disturbance to site mobility, traffic and stored away from drainage paths and suitably covered to avoid washout.

Demolition has to be carried out with the minimum use of machinery and sprinkling of water should be done appropriately.

Suitably arranged barge may be used where access through existing roads is not available.

Construction debris management plan must be worked out prior to construction begins.

Social:

Fixing warning signs at appropriate locations and proper fencing are needed as safety measures. Also, avoidance of slippery conditions along roadsides and pavements and walking surfaces have to be ensured.

Ecological:

N/A

34


Mitigation Measures

Excavation for the gabion wall construction and coffer damming

Physical:

The construction of gabion walls along the canal embankment for bank strengthening and stabilization would require substantial excavation close to the existing earth embankments. Such deep excavations in saturated week soil would result in collapsible vertical soil faces and increased susceptibility to erosion and liquefaction leading to bank failures.

Excessive vibration during hydraulic driving of sheet piles for coffer damming may weaken adjacent soil layers while it may also affect nearby foundations and other structures.

Physical:

Vertical and near vertical soil embankments and excavation faces in saturated, sandy/peaty soils in the area should always be protected by shoring or installation of sheet piles/coffer damming.

Coffer damming is required to contain and divert movement of canal water, to prevent slope failures at soil embankments/ near vertical excavation faces and to provide a reasonably dry construction area for the laying of screed concrete base (if required by design) and interlocking rubble work arrangement during gabion wall construction. The excavations in saturated soil may lead to failure for collapsible soil faces

Minimum driving power should be used where the installations are located close to sensitive/load bearing structures to avoid differential settlements, cracks and other undesirable deformations in soil subsurface structure.

Excavated material from trenches and side faces for the erection of gabion walls should be properly stored and disposed at selected safe disposal locations.

35


Mitigation Measures

Social:


Ecological:

Temporary distraction of fish

Social:

Ensure that the present access on the canal bank to some houses be not disturbed. Present access on the canal bank should be incorporated into the canal reservation so that it could be used for canal maintenance as well as the access to the houses.

Fixing warning signs at appropriate locations and proper fencing are needed as safety measures. Also, no slippery conditions along roadsides and pavements and walking surfaces have to be ensured.

Ecological:

This effect is temporary in nature. Ensure not to leave any material, chemical or any other substance that will eventually get washed away into the drain that could create toxic effects particularly to fingerlings.

Material transport and storage

Physical:

Emission of dust and noise due to transport of material

Physical:

The construction materials intended for temporarily storage should be properly stockpiled in most appropriate areas in the site to avoid disturbance to site mobility, traffic and stored away from drainage paths and suitably covered to avoid

36


Mitigation Measures

Social:

Inconvenience to the neighbours

washout.

Dust emissions should be controlled by wet spraying of construction sites and roads which are used for transportation of construction materials at regular intervals.

Dust barriers should be erected if there are houses nearby stockpiles and tarpaulin covering is mandatory on trucks / lorries which are used for transporting materials.

Vehicles should be maintained in good condition and regularly maintenance in good conditions so that noise generating from wear and tear will be minimal.

Suitably arranged barge may be used for access if existing roads are not available.

Social:

Construction vehicles and equipment should be parked at suitable locations without hindering the day to day

residential and urban activities.

Warning signs at appropriate locations and proper temporary

37


Mitigation Measures

Ecological:

No impact

fencing are needed as safety measures.

Ecological: N/A

Construction of flow guidance walls for Main Drain bank protection

New Gabion walls: 1450 m

New sheet pile walls: 57 m

Rehabilitation of gabion walls: 778 m


Physical:

Improper alignment of flow guidance walls will lead to diverted flows, increased flow velocities causing significant erosion of soil embankments adjacent to important structures, loosening bank support and weakening of the interlocking of rubble used causing immature failure of gabion structure before its intended design life.

Additional excavation and dredging if required will lead to undesirable environmental

Physical:

Lined-concrete flow guide walls designed following appropriate design guidelines and correct construction methodologies should be used where it is necessary to control bottom and side erosion when the gabions walls are expected to get exposed to adverse flow regimes at bend locations, changing sections, drop points, etc.

All excavated and excavated materials arising from additional work should be properly stored and disposed at selected safe disposal locations as per recommendations given above.

Social:

On the left bank where new gabion walls are proposed there are a few houses located, getting the access from canal bank. In such locations make sure that the present access on the canal

38


Mitigation Measures

consequences.

Social:


Ecological:

No impact

bank to those houses be not disturbed. Present access on the canal bank should be incorporated into the canal reservation so that it could be used for canal maintenance as well as the access to the houses.

Ecological:

N/A

Reinstatement of storm water drainage connections (hume pipes) to Main Drain through gabion walls and introduction of catch pits wherever required.

Physical:

Erosion of soil from adjacent structures leading to loosening of bank support will lead to weakening of the interlocking of rubble used causing immature failure of gabion structure before its

Physical:

Strom water connections across the gabion walls should be provided using hume pipes or box culverts of adequate size according to pre-determined design storm events and return periods.

Catch pits should be provided at suitable spacing to remove excessive fines through settlement. Catch pits should be

39


Mitigation Measures

intended design life. Blockage due to accumulation of fines due to cross drainage flows will lead to pore pressure build-up behind the gabion structure, leading to unbalanced pressure forces, making the structure susceptible to failure by toppling.

Social:

No significant impact

Ecological:

No impact

regularly cleaned and maintained in proper order. Fines removed should be properly disposed to avoid them joining flow paths again.

Social:

N/A

Ecological:

N/A

Backfilling of banks behind the gabions, turfing and planting of trees

Physical:

Selection of below grade fill materials will not attain required soil strengths after compaction and will lead to differential settlements

Physical:

Backfill materials should be selected after proper analyses of soil characteristics. Adequate compaction should be applied to attain required soil strengths in banks and embankments.

The construction materials intended for temporarily storage

40


Mitigation Measures

causing the gabion walls to misalign and fail.

Social:

Inconvenience to present residents and pedestrians and potential accidents if the heavy equipment are not handled with great care.

Ecological:

No impact

should be properly stockpiled in most appropriate areas in the site to avoid disturbance to site mobility, traffic and stored away from drainage paths and suitably covered to avoid washout.

Social:

Close supervision by the field technical staff is necessary to make sure that no accidents to people and damage to existing houses happen.


Ecological:

N/A

Reinstatement of maintenance road (width: 3 m) on left bank and construction of road side drain and cross drainage to the canal.

Physical:

Lack of side drains and toe drains of adequate sizes alongside of the maintenance roads will lead to localized ponding in road pavements and weakening of soil sub-

Physical:

Side drains and toe drains of adequate design sizes should be provided alongside of the maintenance roads and proper cross drainage structure should be provided where necessary to divert accumulated flows to the main drains.

The construction materials intended for temporarily storage

41


Mitigation Measures

base underneath.

Social:

Inconvenience to present residents and pedestrians

Ecological:

No impact

should be properly stockpiled in most appropriate areas in the site to avoid disturbance to site mobility, traffic and stored away from drainage paths and suitably covered to avoid washout.


Social:

This activity would be a social benefit to the people as the maintenance road will also become access road to their houses.

Close supervision by the field technical staff is necessary to make sure that no accidents to people and damage to existing houses happen.

Ecological:

N/A

Aluth Mawatha Culvert Improvement:

Physical:

Temporarily blockage to

Physical:

Construction should be carried out during dry weather periods

42


Mitigation Measures

- Demolish and reconstruct 3.0 x 3.5 x 12 m reinforced concrete box culvert

- Connection of box culvert to existing 3.0 x 3.0 mm box drain leading to Mutwal Tunnel.

- Reinstatement of Aluth Mawatha at culvert locations

cross drainage flows may occur during construction activities. De-watering and diversion of flows may be needed to maintain undisturbed canal flows and establish required dry conditions for construction purposes.

Construction debris arising from the demolition of pavement layers and existing reinforced concrete culvert may cause adverse environmental effects like blockage of surface drainage and site mobility, washout of fines, dust and increased accident risk, if not properly handled, stored and disposed.

If the connection between the newly constructed culvert and existing box drain leading to

when the canal flow is low and almost stagnant to minimize the need for pumping and/or adequate flow diversions, dewatering, pumping should be arranged to maintain required cross drainage flows and to provide required dry conditions for construction activities while avoiding flooding and temporarily ponding issues.

Construction debris should be properly handled, stored and eventually disposed, minimizing undesirable environmental consequences at all times. Material recycling is promoted to minimize debris generation and wastage.

Proper backfill materials should be selected after carrying our required field/laboratory tests and optimum compaction conditions should be maintained to attain maximum possible soil strengths after compaction of cover layers.

Catch pits, drain inlet sediment traps/barriers, turbidity curtains should be used to minimize washout of fines and silting effects in the downstream. Energy dissipaters and drops should be used where necessary to reduce flow velocities to reduce erosion and cavitation risks.

Minimum flow velocities required flow self cleansing of drains/structures should be maintained by providing required design gradients in drains, toe drains to minimize siltation.

43


Mitigation Measures

Mutwal Tunnel is not properly designed, the cross drainage flows will be disrupted due to inadequate gradients while turbulence due to drops/humps may cause erosion and cavitation effects.

Inadequate backfill cover above culvert apex level may lead to inadequate load distribution and excessive loads on the box frame. Selection of below grade fill materials that would not attain required soil strengths after compaction and will lead to differential settlements in cover layer above box culvert causing the pavement layers to develop differential settlements and fail.

Regular maintenance and cleaning of sediment traps, catch pits is highly recommended.

Checking of compaction achieved for backfill material would be done on regular basis.

Frequent cleaning must be undertaken in order to keep the effective areas devoid of such materials.

44


Mitigation Measures

Sediment deposit leading to excessive siltation may reduce expected design flow capacities during operational phase.

Social:

Disturbance to vehicular and pedestrian movement.

Ecological:

No impact

Social:

Provide adequate de-routing facilities and fix sign boards to efficiently re-direct the traffic towards their destinations. St. Andrew’s Road, Mattakuliya Road and Ellie House Road can be use as alternative routes.

Ecological:

N/A

Renovation of existing box drain (covers of the openings - 6 Nos.) connecting Aluth Mawatha culvert & Mutwal Tunnel and anticipated catch pits carrying storm water.

Physical:

Temporarily blockage to cross drainage flows may occur during construction activities. De-watering and diversion of flows may be needed to maintain

Physical:

Adequate flow diversions, dewatering, pumping should be arranged to maintain required cross drainage flows and to provide required dry conditions for construction activities while avoiding flooding and temporarily ponding issues.

Construction debris should be properly handled, stored and

45


Mitigation Measures

undisturbed canal flows and establish required dry conditions for construction purposes.


If the connection between the newly constructed culvert and existing box drain leading to Mutwal Tunnel is not properly designed, the cross drainage flows will be disrupted due to inadequate gradients while turbulence

eventually disposed, minimizing undesirable environmental consequences at all times. Material recycling is promoted to minimize debris generation and wastage.

Proper backfill materials should be selected after carrying our required field/laboratory tests and optimum compaction conditions should be maintained to attain maximum possible soil strengths after compaction of cover layers.

Catch pits, drain inlet sediment traps/barriers, turbidity curtains should be used to minimize washout of fines and silting effects in the downstream. Energy dissipaters and drops should be used where necessary to reduce flow velocities to reduce erosion and cavitation risks.

Minimum flow velocities required flow self cleansing of drains/structures should be maintained by providing required design gradients in drains, toe drains to minimize siltation. Regular maintenance and cleaning of sediment traps, catch pits is highly recommended.

46


Mitigation Measures

due to drops/humps may cause erosion and cavitation effects.

Inadequate backfill cover above culvert apex level may lead to inadequate load distribution and excessive loads on the box frame. Selection of below grade fill materials that would not attain required soil strengths after compaction and will lead to differential settlements in cover layer above box culvert causing the pavement layers to develop differential settlements and fail.

Sediment deposit leading to excessive siltation may reduce expected design flow capacities during operational

Checking of compaction achieved for backfill material would be done on regular basis.

Frequent cleaning must be undertaken in order to keep the

47


Mitigation Measures

phase.

Social:

Disturbance to the movement of people and potential accidents when the box drain covers are replaced as the access to the settlement lies on this box drain.

Ecological:

No impact

effective areas devoid of such materials.

Social:

This activity will be carried out section by section and the box drain covers are pre-cast (no in situ construction will take place other than small repairs) and thus removal and replacing will take very short period of time and thus impact would be negligible. Access to the settlement along the box drain will not be an issue as two alternative routes are available.

Ecological:

N/A

Replacement of covers of Mutwal Tunnel manholes (03 Nos.)

Stream lining of inlet area to suit the transition

- Introducing a trash screen - Formation of 2 Nos. new

storm water manholes at

Physical:

If the transition is not well aligned and properly designed, excessive turbulence causing erosion and cavitation risk, either reduced flow velocities causing siltation or increased flow velocities causing erosion/cavitation, spilling

Physical:

Proper design and construction of the transition using precise alignment and correct dimensions following related guidelines and specification is needed to avoid undesirable environmental consequences listed as above.

Installation of trash screens and manholes will reduce accumulation of debris while allowing ease of access to regular maintenance activities.

48


Mitigation Measures

Mutwal inlet and connection of the above two to inlet areas.

- Construction of boundary fence around the inlet areas a (with a gate) as a safety measures.

and overtopping due to inadequate capacity may occur.

If the trash screen is not properly installed using correct dimensions and proper alignments, trash may not be adequately trapped lading to debris accumulation inside the culvert area and flows may be disrupted leading to overtopping and localized ponding.

Lack of adequate accessibility for maintenance activities may lead to blocking of the system reducing design capacity.

Social:

Blockage of solid waste in the trash screen will lead to temporary ponding where

Frequent maintenance of all blocking areas needs to be undertaken.

Social:

Frequent removal of material getting stuck in front of screen needs to be undertaken. Pesticide application for mosquitoes

49


Mitigation Measures

water quality could get degraded causing inconvenience to people particularly with the threat of mosquito breeding.

Ecological:

Open pits and drains may allow animals, particularly domestic ones, to creep into the tunnel and get trapped inside

must be done on regular basis.

Ecological:

This is a very temporary impact and such locations where animals can creep in could be covered to avoid any potential accidents to animals.

Stream lining the Mutwal Outfall Physical:

If the streamlining of the structure at sea outfall is not carried out properly, excessive turbulence causing erosion and cavitation risk, either reduced flow velocities causing siltation or increased flow velocities causing erosion/cavitation may occur.

Physical:

Streamlining should be carried out ensuring that the required gradients to maintain design hydraulic flows are not altered or disrupted.

Adequate concrete cover should be provided to ensure that the reinforcements are not constantly exposed to saline water.

50


Mitigation Measures

Exposure of reinforcements due to deterioration of the concrete cover will lead to the disruption of the structural performance of the outfall.

Social:

Unsound walls may cause inconvenience to the neighbours

Ecological:

No Impact

Social:

Sound construction should be guaranteed through proper supervision.

Ecological:

N/A

51

8. Conclusion and Screening Decision

Summary of environmental effects: Assuming that all mitigation measures are implemented as proposed, the following effects can be predicted

Key project activities Potential Environmental Effects Significance of the environmental effect with mitigation in place

NS- Effect not significant, or can be rendered insignificant with mitigation SP - Significant positive effect SN - Significant negative effect U - Outcome unknown or cannot be predicted, even with mitigation NA – Not applicable

Site preparation including provision of access roads, material storage yards

Physical:

Emission of dust

Social:

Disturbance to pedestrian movement, accessibility to houses.

Ecological:

No impact

NS

NS

NS

52

Temporary shifting & relocating of utility posts (electricity, water, sewer & telecom).

(This is only for re-construction of Culvert across Aluth Mawatha Road)

Physical:

No impact

Social:

Disturbance to pedestrian and vehicular movement.

Ecological:

No impact

NS NS NS

Canal bank/bottom excavation, dewatering and disposal of bottom sediments

Physical:

Excavations of canal banks and excavation of the canal bed close to the sides may be needed during proposed construction activities to provide the base layer for embankment and gabion wall construction/ rehabilitation and for maintaining the required design depths in the existing canals. These activities would degrade water quality by mixing of fines and potentially contaminated material into downstream areas of the canal and ground water.

The low water table may cause dewatering a crucial issue to reduce pore pressure build up, slope instability and transport of fines.

SN

53

Dewatering may also be needed to carry out construction activities without interruption in canal embankments especially for gabion wall construction and widening, and for other excavated areas during the periods of high groundwater table.

Dewatering may cause surface ponding of removed water if proper drainage is not allowed, especially when the upper soil layers are saturated due to recent storm events. Excessive dewatering may cause water table to decline rapidly, lowering soil pore pressure and sinking and localized land subsidence effects adjacent to existing load bearing structures.

Stock piling of excavated material, soil, debris and other material may block surface drainage paths causing localized flooding during constructional and operational periods.

If not properly stored and adequately covered, fine material washout may significantly degrade groundwater and surface water quality in canals, inland reservoirs and sea outfalls, while increasing risk of slope failures, siltation and blockage of structures.

SN

NS

NS

SN

54

Social:

Odour problems

Ecological:

Smothering of benthic fauna

NS

NS

Removal of temporary structures, debris, demolition waste and other solid waste along the banks

Physical:

Emission of dust and noise

Disturbances to traffic and pedestrians during storage of material and debris.

Social:


Ecological:

No impact

NS

NS

NS

NS

Excavation for the gabion wall construction and coffer damming

Physical:

The construction of gabion walls along the canal embankment for bank strengthening and stabilization would require substantial

NS

55

excavation close to the existing earth embankments. Such deep excavations in saturated week soil would result in collapsible vertical soil faces and increased susceptibility to erosion and liquefaction leading to bank failures.

Excessive vibration during hydraulic driving of sheet piles for coffer damming may weaken adjacent soil layers while it may also affect nearby foundations and other structures.

Social:


Ecological:

Temporary distraction of fish

NS NS NS

Material transport and storage

Physical:

Emission of dust and noise due to transport of material

Social:

NS

56

Inconvenience to the neighbours

Ecological:

No impact

NS NS

Construction of flow guidance walls for Main Drain bank protection

New Gabion walls: 1450 m

New sheet pile walls: 57 m

Rehabilitation of gabion walls: 778 m


Physical:

Improper alignment of flow guidance walls will lead to diverted flows, increased flow velocities causing significant erosion of soil embankments adjacent to important structures, loosening bank support and weakening of the interlocking of rubble used causing immature failure of gabion structure before its intended design life.

Additional excavation and dredging if required will lead to undesirable environmental consequences.

Social:


Ecological:

No impact

NS

NS

NS

NS

57

Reinstatement of storm water drainage connections (hume pipes) to Main Drain through gabion walls and introduction of catch pits wherever required.

Physical:

Erosion of soil adjacent structure leading to loosening of bank support will lead to weakening of the interlocking of rubble used causing immature failure of gabion structure before its intended design life. Blockage due to accumulation of fines due to cross drainage flows will lead to pore pressure build-up behind the gabion structure, leading to unbalanced pressure forces, making the structure susceptible to failure by toppling.

Social:

No significant impact

Ecological:

No impact

NS

NS

NS

Backfilling of banks behind the gabions, turfing and replanting of trees

Physical:

Selection of below grade fill materials will not attain required soil strengths after compaction and will lead to differential settlements causing the gabion walls to misalign and fail.

NS

58

Social:

Inconvenience to present residents and pedestrians and potential accidents if the heavy equipment are not handled with great care.

Ecological:

No impact

NS

NS

Reinstatement of maintenance road (width: 3 m) and construction of road side drain and cross drainage to the canal.

Physical:

Lack of side drains and toe drains of adequate sizes alongside of the maintenance roads will lead to localized ponding in road pavements and weakening of soil sub-base underneath.

Social:

Inconvenience to present residents and pedestrians

Ecological:

No impact

NS NS NS

Aluth Mawatha Culvert Improvement:

Physical:

Temporarily blockage to cross drainage flows

59

- Demolish and reconstruct 3.0 x 3.5 x 12 m reinforced concrete box culvert

- Connection of box culvert to existing 3.0 x 3.0 mm box drain leading to Mutwal Tunnel.

- Reinstatement of Aluth Mawatha at culvert locations

may occur during construction activities. De-watering and diversion of flows may be needed to maintain undisturbed canal flows and establish required dry conditions for construction purposes.


If the connection between the newly constructed culvert and existing box drain leading to Mutwal Tunnel is not properly designed, the cross drainage flows will be disrupted due to inadequate gradients while turbulence due to drops/humps may cause erosion and cavitation effects.

Inadequate backfill cover above culvert apex level may lead to inadequate load distribution and excessive loads on the box frame. Selection of below-grade fill materials that would not attain required soil strengths after compaction and will lead to differential settlements in cover

NS

NS

NS

NS

60

layer above box culvert causing the pavement layers to develop differential settlements and fail.


Social:

Disturbance to vehicular and pedestrian movement.

Ecological:

No impact

NS

NS

NS

Renovation of existing box drain (covers of the openings - 6 Nos.) connecting Aluth Mawatha culvert & Mutwal Tunnel and anticipated catch pits carrying storm water.

Physical:

Temporarily blockage to cross drainage flows may occur during construction activities. De-watering and diversion of flows may be needed to maintain undisturbed canal flows and establish required dry conditions for construction purposes.

Construction debris arising from the demolition of pavement layers and existing reinforced concrete culvert may cause adverse

NS

NS

61

environmental effects like blockage of surface drainage and site mobility, washout of fines, dust and increased accident risk, if not properly handled, stored and disposed.

If the connection between the newly constructed culvert and existing box drain leading to Mutwal Tunnel is not properly designed, the cross drainage flows will be disrupted due to inadequate gradients while turbulence due to drops/humps may cause erosion and cavitation effects.

Inadequate backfill cover above culvert apex level may lead to inadequate load distribution and excessive loads on the box frame. Selection of below-grade fill materials that would not attain required soil strengths after compaction and will lead to differential settlements in cover layer above box culvert causing the pavement layers to develop differential settlements and fail.


Social:

NS

NS

NS

62

Disturbance to the movement of people and potential accidents when the box drain covers are replaced as the access to the settlement lies on this box drain.

Ecological:

No impact

NS

NS

Replacement of covers of Mutwal Tunnel manholes (03 Nos.)

Stream lining of inlet area to suit the transition

- Introducing a trash screen

- Formation of 2 Nos. new storm water manholes at Mutwal inlet and connection of the above two to inlet areas.

- Construction of boundary fence around the inlet areas a (with a gate) as a

Physical:

If the transition is not well aligned and properly designed, excessive turbulence causing erosion and cavitation risk, either reduced flow velocities causing siltation or increased flow velocities causing erosion/cavitation, spilling and overtopping due to inadequate capacity may occur.

If the trash screen is not properly installed using correct dimensions and proper alignments, trash may not be adequately trapped lading to debris accumulation inside the culvert area and flows may be disrupted leading to overtopping and localized ponding.

Lack of adequate accessibility for maintenance activities may lead to blocking of the system

NS

NS

NS

63

safety measures. reducing design capacity.

Social:

Blockage of solid waste in the trash screen will lead to temporary ponding where water quality could get degraded causing inconvenience to people particularly with the threat of mosquito breeding.

Ecological:

Open pits and drains may allow animals particularly creepers to enter into the tunnel and get trap inside

NS

NS

Stream lining the Mutwal Outfall

Physical:

If the streamlining of the structure at sea outfall is not carried out properly, excessive turbulence causing erosion and cavitation risk, either reduced flow velocities causing siltation or increased flow velocities causing erosion/cavitation may occur.

Exposure of reinforcements due to deterioration of concrete cover will lead to disrupt structural

NS NS

64

performance of the structure.

Social:

Unsound walls may cause inconvenience to the neighbors

Ecological:

No Impact

NS NS

65

9. Screening Decision Recommendation:

Final recommendation

Majority of the potentially adverse effects can be classified as general construction related impacts and are mitigatable with good construction and site management practices. The public is generally supportive of the project and their concerns do not warrant further assessment. Therefore, a stand- alone Environmental Assessment is not required and, the Environmental Management Plan provided with this report would be sufficient to mitigate the identified impact. However, the following specific recommendations given in the EMP are of utmost importance to be implemented.

A sediment quality testing for toxicity and the quantification of excavated material that will be removedl must be undertaken by the SLLRDC. This is the only potentially significant issue identified. Depending on the results of the sediment quality testing the excavated material should be disposed as specified in the EMP. If not the excavated material can be stored in a suitable site and subsequently used for refilling once the construction of gabion wall is done or even disposed to a municipal waste dump.

Safe handling of the excavated material with a proper plan for disposal including transport must be finalized prior to commencement of the project. Although the draft tender documents would be ready by 31/12/2011, they should be updated based on the results of the sediment testing and subsequent requirements, prior to being advertised.

Construction debris management plan must be worked out and implemented.

Heavy vehicles i.e., large trucks, should not be allowed for material transport. Only small vehicles such as tractors, carts will be promoted particularly in the areas of underserved settlements.

Restoration of existing gabion walls must be done with extreme care so as not to make any collapse of remaining portions by ensuring proper state of art engineering applications.

Sheet pile portion must be done with minimal damage to nearby infrastructure. However if damage is inevitable, compensation should be paid appropriately.

66

Construction activities should be encouraged during dry season so that impacts due to water levels will be minimal. At the Mutwall outfall outlet structure, extreme care must be taken in the case of sea water intrusion for the purpose of promoting flushing of pollutants as the lining of the tunnel or open channel may not be fully water tight. If the lining is not water tight, concrete structures could be corroded and nearby groundwater could go brackish or saline casing foundations be perished due to corrosions. Hence water tightness of the conveyer system in areas where concrete cross sections are available must be tested and guaranteed for. Transport of materials for sections of gabions where there is no access, head transport must be allowed with a slightly higher rate.

10. EMP implementation responsibilities and costs The overall responsibility of ensuring compliance with safeguard requirements for the sub-project lie with the SLLRDC. Specifically, it will be responsible for undertaking sediment quality testing in selected locations of the Main Drain where the project interventions are proposed for, estimation of excavated material quantities generated and guiding the contractor on suitable disposal methods. The contractor will be responsible for implementing all other provisions in the EMP that relate mostly to good construction planning, site management and public safety practices with no additional costs involved. The SLLRDC will also be responsible for taking into consideration all recommendation in the EMP relating to designs and ensure they are revised, if necessary, to address the concerns raised. The additional cost involved in implementing the EMP relate to (a) undertaking sediment quality tests and (2) disposal of excavated material if contamination is established. Environmental monitoring will be carried out largely through compliance monitoring using the checklist provided in the EMF by the Environmental Officer of the CMC and the contractor jointly.

67

As such, the only additional costs envisaged are explained below:

Item Cost (Rs) Implementation Responsibility

Sediment quality testing – 3samples

For following physical and chemical parameters

Particle size distribution, pH, Sulphate, Chloride, Total Organic Carbon, Fe, Cd, Ni, Zn, Cu, Cr, Al, Pb, Mn, Ca, Mg, Hg, As and leachability test for heavy metals

The testing will be done in early January 2012

180,000 SLLRDC

Disposal of excavated material The cost of mitigation is hard to estimate at this stage as the quantities of material, quality of pollutants/substances, and sites for disposal etc. are undecided. The consultant will work with the SLLRDC for estimating the mitigation cost once results of the sediment quality test

Contractor

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Screening report completed by Dr. Mahesh Jayaweera, Team Leader

University of Moratuwa

Tel: 0777320590

email: [email protected]

Name/Designation/Contact information

Date Signature

Screening report reviewed by Name/Designation/Contact information

Date Signature

Approved by Name/Designation/Contact information

Date Signature

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11. Details of Persons Responsible for the Environmental Screening (1) Dr. Mahesh Jayaweera, PhD, BSc in Civil Eng (Hons.), MIE (SL), CEng. – Team Leader (Overall coordination and planning) Experience: Team Leader/Consultant/Expert for more than 60 EIA and IEE studies during the past 15 years (2) Professor Mrs. Niranjanie Ratnayake, BSc in Civil Eng (Hons.), MSc, FIE (SL), CEng. – Environmental assessment specialist Experience: Team Leader/Consultant/Expert for more than 40 EIA and IEE studies during the past 20 years (3) Dr. Jagath Manatunge, PhD, MSc, DIC, BSc in Civil Eng (Hons.), MIE (SL), CEng. – Environmental Engineer (Noise, Water, Wastewater, Vibration, Air) Experience: Team Leader/Consultant/Expert for more than 40 EIA and IEE studies during the past 12 years (4) Dr. Lalith Rajapakse, PhD, MEng, BSc in Civil Eng (Hons.), MIE (SL), CEng. – Civil Engineer (Hydrology, Geology, other civil engineering aspects) Experience: Consultant/Expert for more than 20 EIA and IEE studies and assignments mainly related to hydrological during the past 6 years (5) Mr. Hemantha Jayasundara, BA (Hons.), MSc (Town and Country Planning), PG Dip in Urban Development, PD Dip in Environmental Sci. –Urban Planner Experience: More than 20 years as a Consultant/Expert on Urban and Regional Planning, Urban Design, Disaster Management, Environmental Management, Projects Management etc. (6) Dr. Anusha Kasige, PhD, MSc, BSc in Zoology – Ecologist (Flora, Fauna, Ecosystems) Experience: more than 15 EIA and IEE studies and ecological studies during the past 5 years

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References

Cooray, P.G.(1984). An introduction to the geology of Sri Lanka (Ceylon), with a foreword by John Sutton, National Museums of Sri Lanka Publication, Colombo, Sri Lanka.

Greentech (2011). Environmental Assessment Final Report for Metro Colombo Urban Development Project, Vol. 1, Greentech Consultants (Pvt) Ltd., Colombo 5, Sri Lanka.

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Annex 1:

Photographs of some of the important locations along project roads

Aluth Mawatha and Mutwall outfall

1. Canal embankment

Fig.A‐ 1 Lat‐6.957060 Lon‐79.863720 Fig.A‐ 2 Lat‐6.957270 Lon‐79.863380


Fig.A‐ 6 Lat‐6.956460 Lon‐79.864670 Fig.A‐ 5 Lat‐6.95623º Lat‐79.86483º

Fig A‐1. General view of the canal and the right bank

Fig A‐2. General view of the canal and the right bank

Fig A‐3, General view of the canal and the left bank

Fig A‐4. General view of the canal and the left bank

Fig A‐5. View of the canal from the railway bridge

Fig A‐6. Canal near the railway bridge.

2. Outfall (Ceylon Fisheries Corporation)

2.


Fig.A‐ 9 Lat‐6.961970 Lon‐79.858020 Fig.A‐ 10 Lon‐6.958220 Lat‐79.861750

Fig A‐7. Mutwal outfall

Fig A‐8. About 40 m upstream of the outfall

Fig A‐9. Outlet from the tunnel

Fig A‐10. Outlet from the tunnel

3. Culvert at Aluth Mawatha

Fig.A‐ 14 Lat‐6.957820 Lon‐79.862740

Fig.A‐ 11 Lat‐6.957820 Lon‐79.862740

Fig.A‐ 13 Lat‐6.957810 Lon‐79.862680

Fig.A‐ 12 Lat‐6.957610 Lon‐79.862840

Fig A‐11. Culvert at Aluth Mawatha

Fig A‐12. The Bo Tree located very close to the culvert

Fig A‐13. View from the Aluth Mawatha towards canal upstgream

Fig A‐14. Gabion walls near the culvert which need rehabilitation

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Annex 2: Detailed drawings of project components

Main Drain

Proposed bank protection

Proposed bank protection

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