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GEO TAIL PTY LTD

MINE RESIDUE CONSULTING SERVICES

LEOPARD COURT BUILDING

1 St. FLOOR, SOUTH WING,

c/o JEROME & KARIBA STREET,

LYNWOOD GLEN

TEL : +27 12 348 1051

FAX : +27 86 686 9023

EMAIL : [email protected] or [email protected]

Project: Kangra Coal

Sample Number: 2nd Stage Taotal Discard

Sample Position: -

Test: Falling Head Permeability (Page 1/2)

Sample Date: -

Lab Number: 14/313

Test Date: 19-Jun-14

Preparation:

Method:

Specified Dry Density (kg/m3) & Opt. Moisture (%): 1710.0 @ 5.8%

Target of Dry Density (%): 90%

Target Dry Density (kg/m3) & Moisture (%): 1539.0 @ 5.8%

Sample Diam. D (mm) : 63.50 Sample Moisture :

Sample Length L (mm) : 64.63 Tin No: D037

Moist soil mass (g) : 297.79 Tin Weight (g): 83.86

Particle Density ρs : - Tin & Wet Soil (g): 288.970

Bulk Density (kg/m3) : 1454.92 Tin & Dry Soil (g): 277.790

Dry Density (kg/m3) : 1375.61 Moisture Content: 5.8%

Material after MOD AASHTO determination sieved through 4.75mm sieve

compacted in 3 layers by hand tamping.

250 ORION AveMonument Park 0181

PO Box 26272Monument Park0105

Tel/Fax 012 346 7586Cell: 082 375 [email protected]

Reg. No: cc 200004833323

Actual Dry Density (kg/m3) & Moisture (%) Achieved: 1375.6 5.8%

Actual Density Achieved(%): 80.4%

Calculations:

Volumetric Tube:

Sample Area A: 3166.9 mm2

h1: Top (cm): 354.0

Sample Volume V: 204.7 cm3

h2: Bottom (cm): 294.5

Voids Ratio (ρS/ρD-1): - V1 Top (cm3): 0

V2 Bottom (cm3): 100

Temperature (°C): 22 Tube Area a (mm2): 168.1

Permeability: kT = 3.84(aL/At)log10(h1/h2)x10-5 m/s (K.H. Head)

Permeability k = 3.7E-06 m/s


Sample Number: 2nd Stage Taotal Discard

Sample Position: -

Test: Falling Head Permeability (Page 2/2)

Sample Date: -

Lab Number: 14/313

Test Date: 19-Jun-14

Measurement Data:

Date & TimeElapsed Time

(minutes)

Top Reading -

In (ml)

Height above

outlet h (mm)

Height h1 h2, h3

per Run (mm)

Height Ratio

(h1/h2)

Falling Head

Permeability

(m/s)

Run 1

6/19/14 11:26 0 0.0 3540.0 3540.0 1.092 5.84E-06

6/19/14 11:26 1 50.0 3242.5 3242.5 5.54E-06

6/19/14 11:27 2 100.0 2945.0 2945.0 1.101 5.24E-06

Run 2

6/19/14 11:29 0 2.0 3528.1 3528.1 1.068 5.19E-06

6/19/14 11:29 1 40.0 3302.0 3302.0 5.03E-06

6/19/14 11:30 2 80.0 3064.0 3064.0 1.078 4.86E-06

Run 3

6/19/14 11:32 0 0.0 3540.0 3540.0 1.092 5.12E-06

6/19/14 11:32 1 50.0 3242.5 3242.5 4.76E-06

6/19/14 11:34 2 100.0 2945.0 2945.0 1.101 4.40E-06

Run 4

6/19/14 11:35 0 0.0 3540.0 3540.0 1.092 4.08E-06

6/19/14 11:36 1 50.0 3242.5 3242.5 3.88E-06

6/19/14 11:37 3 100.0 2945.0 2945.0 1.101 3.67E-06

Run 5

6/19/14 11:40 0 0.0 3540.0 3540.0 1.092 3.78E-06

6/19/14 11:41 1 50.0 3242.5 3242.5 3.65E-06

6/19/14 11:42 3 100.0 2945.0 2945.0 1.101 3.53E-06

Run 6

6/19/14 11:45 0 0.0 3540.0 3540.0 1.092 3.64E-06

6/19/14 11:46 1 50.0 3242.5 3242.5 3.52E-06




Reg. No: cc 200004833323

6/19/14 11:46 1 50.0 3242.5 3242.5 3.52E-06

6/19/14 11:48 3 100.0 2945.0 2945.0 1.101 3.40E-06

Run 7

6/19/14 11:53 0 0.0 3540.0 3540.0 1.092 3.78E-06

6/19/14 11:54 1 50.0 3242.5 3242.5 3.75E-06

6/19/14 11:55 3 100.0 2945.0 2945.0 1.101 3.72E-06

Run 8

6/19/14 11:56 0 0.0 3540.0 3540.0 1.092 3.80E-06

6/19/14 11:57 1 50.0 3242.5 3242.5 3.74E-06

6/19/14 11:58 3 100.0 2945.0 2945.0 1.101 3.67E-06

Run 9

6/19/14 11:57 0 0.0 3540.0 3540.0 1.092 3.80E-06

6/19/14 11:58 1 50.0 3242.5 3242.5 3.74E-06

6/19/14 11:59 3 100.0 2945.0 2945.0 1.101 3.67E-06


Sample Number: 2nd Stage Total Discard

Test:

Sample Received:

Lab Number: 14/313

Date Tested:

14/313 / A 14/313 / B 14/313 / C

m1

m2

m3

m4

ρs

ρs

PARTICLE DENSITY

13-Jun-14

20-Jun-14

Soil Sample No & Ref Number

Density Bottle No 7 8 9

Volume (ml) 504.800 498.530 498.600

Container empty, dry, stopper (g) 155.310 168.840 188.000

Dry Soil (±10g) & Container (g) 305.490 319.120 337.910

De-aired Soil & Container after

25˚C bath(g)737.650 745.020 763.620

Bath Temp (˚C) 25.0 25.0 25.0

Container filled de-aired (g) 660.110 667.370 686.600

Particle Density (g/cm3) 2.061 2.063 2.051

Averaged Particle Density (g/cm3) 2.06




Reg. No: cc 200004833323


Test:

Date:

14/313 - - - - - -

- - - - - - -

200 100 - - - - - -

100 100 - - - - - -

63 100 - - - - - -

53 97 - - - - - -

37.5 79 - - - - - -

26.5 57 - - - - - -

19.0 44 - - - - - -

13.2 33 - - - - - -

9.5 26 - - - - - -

6.7 17 - - - - - -

4.75 13 - - - - - -

2.36 10 - - - - - -

1.18 7 - - - - - -

- - - -

Depth / Position

GRADING & PARTICLE DENSITY

- - -

Lab Sample No.

Client Sample No.2nd Stage

Total

Discard

-

Description / NotesBlack

Gravel- -

Percentage Passing Size (mm)

23-Jun-14

- -




Reg. No: cc 200004833323

1.18 7 - - - - - -

0.600 6 - - - - - -

0.425 5 - - - - - -

0.300 4 - - - - - -

0.212 4 - - - - - -

0.150 3 - - - - - -

0.075 2 - - - - - -

0.060 - - - - - - -

0.050 - - - - - - -

0.020 - - - - - - -

0.005 - - - - - - -

0.002 - - - - - - -

Liquid Limit - - - - - - -

Plastic Limit - - - - - - -

Linear Shrinkage - - - - - - -

Plasticity Index - - - - - - -Atterberg

Limits

- -Particle Density 2.06 - - - -

Percentage Passing Size (mm)

0

10

20

30

40

50

60

70

80

90

100

0.0

10

0.1

00

1.0

00

10

.00

0

10

0.0

00

10

00

.00

0

Pe

rce

nta

ge

Pa

ssin

g %

Fraction Size (mm)

GRADINGS

2nd Stage Total Discard -

Kangra Coal

2nd Stage Total Discard

5.8% - - - -

1810.6 - - - -

1710.7 - - - -

- - - - -

Project:

Sample Number:

Test:

Lab no:

Mod. AASHTO Single Point Density

Zero Voids Density (kg/m3)

Test Date: 26-Jul-13

Moisture (%)

Moist Density (kg/m3)

Dry Density (kg/m3)

13/017

1710

5.8%

Max Optimum Dry Density (kg/m3)

Optimum Moisture (%)

Specific Gravity (kg/m3) -




Reg. No: cc 200004833323

1770

1790

1810

1830

1850

Dry

De

nsi

ty (

kg

/m3)

1650

1670

1690

1710

1730

1750

1770

4% 5% 6% 7% 8%

Dry

De

nsi

ty (

kg

/m

Moisture (%)

iLanda Water Services CC

Reg. No.: CK2011/077571/23 PO Box 44961 Linden 2104 Johannesburg, South Africa Tel +27 (0)83 408 3241 Fax +27 (0)86 552 0407 [email protected] http://www.ilandawater.co.za

Member: B Randell BSc Eng (Civil), PhD, PrEng.

www.ilandawater.co.za

REPORT ON

KANGRA POLLUTION CONTROL DAM AND STORM WATER CHANNEL

SIZING

Report No : 0119-Rep-001 Rev0

Submitted to:

Geo Tail (Pty) Ltd P.O. Box 38457

Faerie Glen 0043

DISTRIBUTION:

Geo Tail (Pty) Ltd iLanda Water Services – Library June 2014 0119

June 2014 i 0119-Rep-001 Rev0



TABLE OF CONTENTS

SECTION PAGE

1 INTRODUCTION ....................................................................................... 3

1.1 Study Objectives ................................................................................ 3

1.2 Battery Limits ..................................................................................... 4

2 CLIMATE DATA ......................................................................................... 4

2.1 Evaporation Data ............................................................................... 4

2.2 Rainfall Data ...................................................................................... 5

2.3 Peak Rainfall Data ............................................................................. 7

3 REGIONAL HYDROLOGY ........................................................................ 8

4 WATER BALANCE MODELLING ............................................................. 8

4.1 Description of Operations .................................................................. 8

4.2 Modelling Approach ........................................................................... 9

4.3 Scenarios Modelled ......................................................................... 10

4.3.1 Sources of area information ............................................... 10

4.4 Water Balance Methodology ............................................................ 11

4.4.1 Pollution control dam .......................................................... 11

4.4.2 Catchments ........................................................................ 11

5 RESULTS ................................................................................................ 12

6 CLEAN STORM WATER MANAGEMENT ............................................. 13

6.1 Design Objectives ............................................................................ 13

6.2 Channel Locations ........................................................................... 13

6.3 Catchment Sizes and Flood Peaks .................................................. 14

6.4 Channel Sizing and Specifications ................................................... 14

6.5 Channels Requiring Erosion Protection ........................................... 15

7 CONCLUSIONS ...................................................................................... 15

8 REFERENCES ........................................................................................ 16

LIST OF FIGURES

Figure 1: Colliery location ...................................................................................................... 3

Figure 2: Average monthly rainfall and rain days ................................................................... 6

Figure 3: Daily rainfall record ................................................................................................ 7

Figure 4: Log Extreme Value Type I statistical fit to the annual maximum series................... 8

Figure 5: Three phases of the discard dump ......................................................................... 9

Figure 6: Channel locations. ................................................................................................ 13

June 2014 ii 0119-Rep-001 Rev0



LIST OF TABLES

Table 1: Summary of climate data ......................................................................................... 4

Table 2: Evaporation data used in the modelling ................................................................... 5

Table 3: Summary of rainfall data used in the modelling ....................................................... 6

Table 4: Peak 24-hour rainfall depths for the site .................................................................. 7

Table 5: Areas used in the modelling .................................................................................. 10

Table 6: Summary of the modelling results ......................................................................... 12

Table 7: Summary of flood peak calculations ...................................................................... 14

Table 8: Channel sizing and parameters ............................................................................. 15

LIST OF APPENDICES

None

REVISION TRACKING

Rev 0: Original document

June 2014 3 0119-Rep-001 Rev0



1 INTRODUCTION

Kangra Colliery (Kangra) requires a new discard dump. The storm water from the discard dump will be routed to a pollution control dam to be managed. The discard dump will be constructed on an HDPE liner. All drain water collected on the liner will also be routed to the pollution control dam. Storm water channels will divert clean storm water from upstream catchments around the discard dump. This report documents the methods of analysis and the results of the study, as well as any recommendations that have come from the study.

Kangra is an existing colliery, located close to Heyshope Dam. Kangra is located approximately 40 km west of Piet Retief. The colliery’s location is shown in Figure 1.

Figure 1: Colliery location

1.1 Study Objectives

The study objectives are as follows:

• Determine the water balance for the discard dump and the pollution control dam.

• Size the pollution control dam to comply with Government Notice 704 of the South African National Water Act (GN704). GN704 requires dams to be sized to achieve one spill every fifty years on average.

• Size the clean storm water diversions to comply with GN704.

June 2014 4 0119-Rep-001 Rev0



1.2 Battery Limits

The proposed discard dump, its pollution control dam, its clean storm water diversions and their upstream catchments are included in the battery limits. The plant is outside the battery limits.

2 CLIMATE DATA

The climate data is summarised in Table 1, with more detailed assessments in sections 2.1 to 2.3.

Table 1: Summary of climate data

Parameter Value Mean annual precipitation 772.1 mm

Mean annual evaporation 1400 mm

Wet season rainfall (October to March) 648.7 mm

Dry season rainfall (April To September) 125.1 mm

Wet season evaporation (October to March) 844.9 mm (S-Pan)

Dry season evaporation (April To September) 555.1 mm (S-Pan)

50-year 24-hour peak rainfall 136 mm

100-year 24-hour peak rainfall 160 mm

1 000-year 24-hour peak rainfall 275 mm

2.1 Evaporation Data

Mean annual evaporation data was obtained from the WR2005 database for quaternary catchment W51B (Middleton et al, 2009). Its monthly distribution was sourced from the Water Resources of South Africa Study data set, zone 13A (Midgley et al., 1990). The evaporation data used is summarised in Table 2. The monthly average evaporation was used in the modelling since no daily evaporation data was available.

June 2014 5 0119-Rep-001 Rev0



Table 2: Evaporation data used in the modelling

Month Potential evaporation depth (mm/month)

January 153.7

February 131.5

March 127.3

April 99.0

May 82.3

June 69.2

July 77.6

August 100.1

September 127.0

October 137.1

November 142.7

December 152.7

Total 1400 mm/year 2.2 Rainfall Data

Kangra is located in a summer rainfall area, with almost 84% of the annual rainfall falling between the beginning of October and the end of March.

Rainfall data for the area was obtained from the CCWR (Computing Centre for Water Research, Natal University) database. Gauge number 0407639 (Groot Rietvlei) was used. The record is a good patched daily record starting on 1 July 1929 and ending on 31 August 2000, or over 71 years long. The gauge is located approximately 12.2 km south of Kangra.

The daily rainfall record was used in the time series modelling. This data was statistically analysed and the results of this analysis are presented in Table 3. This data is shown graphically in Figure 2. The full time series of the record is shown in Figure 3.

June 2014 6 0119-Rep-001 Rev0



Table 3: Summary of rainfall data used in the modelling

Month Average rainfall (mm) Average rainfall days October 76.4 5.8

November 117.3 8.3

December 132.5 8.5

January 132.1 8.2

February 107.4 6.9

March 83.1 5.7

April 47.6 3.6

May 19.1 1.7

June 7.0 0.9

July 10.2 0.8

August 10.7 1.2

September 30.5 2.6

Total rain days 54.2 Mean annual precipitation 772.1 mm*

* Note that the mean annual precipitation will not necessarily equal the sum of the monthly averages.

Figure 2: Average monthly rainfall and rain days

0

1

2

3

4

5

6

7

8

9

10

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Av

era

ge

mo

nth

ly r

ain

fall

da

ys

Mo

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ly a

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(m

m/m

on

th)

Ave rainfall

Ave rain days

June 2014 7 0119-Rep-001 Rev0



Figure 3: Daily rainfall record

2.3 Peak Rainfall Data

The daily rainfall record discussed in Section 2.2 was analysed and the annual maximum series was extracted from the data. This annual maximum series was statistically analysed using the UP Flood analysis package to determine various T-year recurrence interval, 24-hour storm depths. A Log Extreme Value Type 1 distribution was selected as the most appropriate statistical fit. This fit is shown in Figure 4. The rainfall record is long, consists of good data, is representative of the site, and is suitable to be used to calculate peak rainfall.

The results from the statistical analysis are presented in Table 4.

Table 4: Peak 24-hour rainfall depths for the site

Recurrence Interval (year) 24-hour rainfall depth (mm) 2 59

10 92

20 109

50 136

100 160

200 188

500 234

1000 275

10 000 471

0

20

40

60

80

100

120

140

160

180

200

mm

/da

y

June 2014 8 0119-Rep-001 Rev0



Figure 4: Log Extreme Value Type I statistical fit to the annual maximum series

3 REGIONAL HYDROLOGY

Kangra is located in quaternary catchment W51B. The mean annual runoff for quaternary catchment W51B is approximately 10% of the mean annual rainfall.

4 WATER BALANCE MODELLING

4.1 Description of Operations

Dry discards are mechanically placed and compacted on the discard dump. The dump is lined with an HDPE liner to limit groundwater pollution. The dump will be constructed in three phases (refer to Figure 5). The liner for each subsequent phase will be constructed while deposition in the current phase is ongoing. This will allow the smooth transition from one phase to the next. The dump will be rehabilitated concurrently.

June 2014 9 0119-Rep-001 Rev0



Figure 5: Three phases of the discard dump

4.2 Modelling Approach

The rehabilitation progress is a significant contributor to the sizing of the pollution control dam. If the rehabilitation is truly concurrent, the pollution control dam capacity will be minimised. This is because areas of the dump that can be considered as dirty are minimised. Runoff from the rehabilitated areas of the dump is assumed to be clean and can be released to the environment. Only runoff from the unrehabilitated areas is assumed to be required to be contained in the pollution control dam. If rehabilitation lags the dump construction significantly, the dump areas considered dirty will be large, thus requiring a large pollution control dam.

It cannot be known how the rehabilitation of the dump will progress during its lifetime. A conservative approach may unfairly penalise the colliery and provide no incentive to concurrently rehabilitate the dump. A modular approach was therefore considered.

The three phases of dump construction are similar sized. The principle of the modular approach is to size a pollution control dam for one phase of the dump. This pollution control dam will service an area equivalent to one phase of the dump being dirty. The largest of the three phases was selected to be slightly conservative. If the rehabilitation is truly concurrent, no more than one phase of the dump should be considered dirty at any point in time and the single pollution control dam will be adequate during the entire life of the dump. If the rehabilitation lags the dump construction, a second and potentially a third pollution control dam of the same size will be required, depending on how much of the dump is

June 2014 10 0119-Rep-001 Rev0



unrehabilitated. As soon as the dirty area exceeds the area of the phase used in this modelling (Table 5), a new pollution control dam of the same size will be required. Up to three pollution control dams will be required if no rehabilitation is done while the dump is constructed. This also has the benefit of delaying capital should a second and third pollution control dam be required.

Runoff from areas that are lined, prior to dump construction should be managed so that it is clean and discharged to the environment. No runoff from lined surfaces has been accounted for. This runoff would significantly increase the required pollution control dam size should it need to be managed in the pollution control dam.

4.3 Scenarios Modelled

Eight scenarios were simulated to comply with GN704 of the South African National Water Act. The scenarios provide a relationship between return pumping capacity and required pollution control dam capacity. If no water is pumped from the pollution control dam, it acts as an evaporation pond. This is one extreme of the relationships. If the pollution control dam is emptied every day, the required capacity equals the volume generated by a 50-year design storm.

Water that is pumped out of the pollution control dam is assumed to be managed elsewhere on the mine, consumed in the plant, stored in another appropriate facility outside of these battery limits or treated to discharge standards and discharged to the environment. The management of this water is beyond the scope of this study.

The areas used in the modelling are summarised in Table 5.

Table 5: Areas used in the modelling

Parameter Area Dump area 256 126 m2

Rehabilitated area 0 m2

Catchment paddocks 32 352 m2

Lined area 0 m2

Total Area 288 478 m2 4.3.1 Sources of area information

The footprints and areas provided in Table 5 were measured off the design drawings provided by Geo Tail (Pty) Ltd.

June 2014 11 0119-Rep-001 Rev0



4.4 Water Balance Methodology

The water balance model consists of a mass-balance model that operates on a daily time step. The model is coded in GoldSim. The dump and paddocks are modelled as catchments. These catchments are calibrated to generate runoff applicable to the components they represent.

4.4.1 Pollution control dam

The water balance around the pollution control dam is modelled in detail. The following hydrological interactions are modelled:

• Inflows o Direct rainfall o Storm water inflows o Drain inflows

• Outflows o Seepage losses (limited due to HDPE liner) o Evaporation losses o Spillage losses (in compliance with GN704) o Return to plant

Evaporation is calculated using the water surface area in the pollution control dam at the time of calculation. The area of the pollution control dam is defined by the area-storage relationship for the dam and is continuously adjusted as storage in the return water changes.

4.4.2 Catchments

The catchments consist of a three-layer cascading soil moisture budgeting system and SCS-based moisture budget equations. This accounts for antecedent moisture conditions in the upper subsurface layers of the catchments. Runoff, infiltration and evaporation are dynamically adjusted to account for antecedent moisture conditions in the catchments.

The interflow and seepage to deep groundwater is calculated using a non-linear decay function that is dependent on the volume of water that infiltrates into the sub-surface layers of the catchment.

June 2014 12 0119-Rep-001 Rev0



5 RESULTS

The results of the simulations are summarised in Table 6. The results show the relationship between pollution control dam capacity and return pumping capacity, to achieve compliance with GN704.

If no water is returned from the pollution control dam, it acts as an evaporation dam. A 1.45 Mm3 dam with an average depth of 2 m will be required to achieve compliance with GN704.

The more water that is pumped out of the pollution control dam, the smaller the capacity required to achieve compliance with GN704. As an example, if water is returned at a maximum rate of 1 100 m3/day, the required pollution control dam capacity reduces to 50 000 m3.

If the pollution control dam is emptied every day, the required capacity equals the volume generated by a 50-year design storm. This is 17 400 m3. This is the minimum pollution control capacity that can achieve compliance with GN704.

Table 6: Summary of the modelling results

Pollution control dam capacity Required return pumping capacity * 1 450 000 m3 0 m3/day

100 000 m3 200 m3/day

75 000 m3 500 m3/day

50 000 m3 1 100 m3/day

40 000 m3 2 200 m3/day

30 000 m3 6 300 m3/day

20 000 m3 16 200 m3/day

17 400 m3 17 400 m3/day

* Note: This full pumping capacity should be used whenever possible. The pollution control dam should be operated empty.

The maximum pump capacities will not always be required. Simulations show that the larger the pump capacity, the less frequent it will be used:

• The full pump capacity for the 100 000 m3 pollution control dam (200 m3/day) will be used about 45% of the time (168 days a year on average).

• The full pump capacity for the 50 000 m3 pollution control dam (1 100 m3/day) will be used about 4% of the time (15 days a year on average).

• The full pump capacity for the 20 000 m3 pollution control dam (16 200 m3/day) will be used about 0.01% of the time (once every 25 years on average).

• The full pump capacity for the 17 400 m3 pollution control dam (17 400 m3/day) will be used less than 0.005% of the time (once every 50 years on average).

June 2014 13 0119-Rep-001 Rev0



6 CLEAN STORM WATER MANAGEMENT

6.1 Design Objectives

The design objectives are as follows:

• Create safe and stable structures and minimise risk to human lives, health, property and the environment

• Comply with relevant legal requirements • Separate clean and dirty storm water as required by the South African National

Water Act, as well as international best practice. The channels are sized to convey the 50-year design flood peak.

• Cost effective construction, operation and closure

6.2 Channel Locations

Two channels have been proposed, and are shown schematically in Figure 6. A local watershed runs generally east-west through the southern end of the phase 2 discard dump footprint. The two channels originate on this watershed. The North Channel runs generally northwards and the south channel runs southwards before turning westwards and north westwards around the southern perimeter of the discard dump.

Figure 6: Channel locations.

June 2014 14 0119-Rep-001 Rev0



6.3 Catchment Sizes and Flood Peaks

The catchments were delineated using 1 m contour data supplied by Geo Tail (Pty) Ltd as well as 5 m contour data sourced from Google Earth®. The catchments are small and the rational method is therefore a suitable method of determining the flood peaks. The old Department of Water Affair’s calculation sheet was used to determine the runoff coefficients. The time-to-concentration of the sub-catchments was calculated using the SCS method which is suitable for relatively undeveloped catchments. Adamson’s TR102 (Adamson, 1981) was used to convert the 24-hour peak rainfall data to rainfall intensities appropriate to the time-to-concentration of the catchments. The 1085 method was used to calculate catchment slopes. The results of these calculations for all sub-catchments are summarised in Table 7.

Table 7: Summary of flood peak calculations

Sub catchment Parameter Value North Channel Catchment size 32.9 ha

Runoff coefficient 0.32

Time to concentration 0.28

Adamson’s TR102 DHour factor (R1) 0.34

Peak rainfall intensity 162 mm/hr

50-yr flood peak 4.7 m3/s

South Channel Catchment size 4.9 ha

Runoff coefficient 0.32

Time to concentration 0.17 → 0.25 hrs used*

Adamson’s TR102 DHour factor (R1) 0.32

Peak rainfall intensity 174 mm/hr

50-yr flood peak 0.8 m3/s

* Note: A Time to concentration of less than 0.25 hrs becomes impractical to use and is not consistent with the use of the Rational Method for flood peak calculations.

6.4 Channel Sizing and Specifications

The storm water channels have been sized assuming unlined channels, and excavated into the ground. The material excavated from the channel should be placed in a berm on the downstream side of the channel. This serves two purposes:

• The berm will increase the capacity of the channel above its design capacity and provide additional freeboard where required.

• The berm allows cost effective construction as load and haul volumes are minimised.

The berm should be compacted and vegetated. A geotechnical investigation of the soils should be undertaken to confirm the compaction specifications. The channel should be kept free of long grass, shrubs and woody vegetation.

June 2014 15 0119-Rep-001 Rev0



The channel was sized to accommodate the flood peak presented in Table 7. The Mannings open channel flow equation was used to calculate flow depth in the channel. A Mannings n of 0.027 was used.

It is good practice to allow a further 0.3 m of freeboard in the channel. This is to allow for wave action and flow surges in the channel. A summary of the channel sizes is presented in Table 8. In order to keep channel depths practical to construct, the freeboard allowance within the channels are varied. Where freeboard within the channels is less than 0.3 m, the berms on the outsides of the channels provide the additional freeboard. A minimum of 0.3 m freeboard is therefore available in the channel.

Table 8: Channel sizing and parameters

Parameter North Channel South Channel Shape Trapezoidal Trapezoidal

Base width 1 m 1 m

Side slopes 1:1.5 (V:H) 1:1.5 (V:H)

Flow depth 0.83 m 0.48 m

Channel depth* 1.1 m 0.8 m

Max flow velocity** 3.7 m/s 2.7 m/s

Flow type at max velocity Supercritical Supercritical

* Note: Channel depths are based on the flattest downstream portion of the channel carrying the full design flow. ** Note: Flow velocities are based on the maximum longitudinal gradient. 6.5 Channels Requiring Erosion Protection

The portion of the North Channel adjacent to Phase 1 and downstream of this will require erosion protection. The flow regime is supercritical and design flow velocities are likely to exceed 3.5 m/s.

The South Channel will require erosion protection once it turns west and north west.

Erosion protection could include concrete, HDPE, grouted stone pitching, Reno matrasses, Armourflex or similar technology.

7 CONCLUSIONS

It is unlikely that an evaporative system will be feasible to manage storm water generated from the discard dump footprint. The simulations show that a 2 m deep pollution control dam with a capacity of 1.45 Mm3 is required to evaporate the dirty storm water generated from the one phase of the dump and remain in compliance with GN704.

June 2014 16 0119-Rep-001 Rev0



If water is pumped out of the pollution control dam, its capacity and footprint can be significantly reduced. The return capacities to achieve compliance with GN704 for a 50 000 m3 and a 100 000 m3 dam are 1 100 m3/day and 200 m3/day respectively. Note that these are return capacities and not continuous returns.

If the pollution control dam is emptied every day, the required capacity equals the volume generated by a 50-year design storm. This is 17 400 m3. This is the minimum pollution control capacity that can achieve compliance with GN704.

The storm water channels are relatively small, since the colliery is located close to local watersheds and catchments are small.

8 REFERENCES

Middleton, B.J. and Bailey, A.K., Water Resources of South Africa, 2005 study (WR2005), 2009. WRC Report No TT 382/08.

Midgley, D.C., Pitman, W.V., Middleton, B.J. Surface Water Resources of South Africa, 1990. WRC Report No 298/2.1/94, Volume 2.

Adamson, P.T., Southern African Storm Rainfall, Department of Environment Affairs, Technical Report TR102, Pretoria, 1981.

ILANDA WATER SERVICES

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