RVM Hydro Electric Project - CESNET 1 Hydro Electric Power...Prepared by Hydro‐Electric Corporation ABN48 072 377 158 t/a Entura 89 Cambridge Park Drive, Cambridge TAS 7170 Australia

Prepared by Hydro‐Electric Corporation ABN48 072 377 158t/a Entura 89 Cambridge Park Drive, Cambridge TAS 7170 Australia

RVM Hydro Electric Project Stormwater Management Plan

7 May 2015

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RVM Hydro Electric Project ‐ Stormwater Management Plan Revision No: 0 7 May 2015

Document information

Title RVM Hydro Electric Project

Stormwater Management Plan

Client organisation RVM Hydro Electric Power

Client contact Niel Theron

Project manager Nicholas West

Revision history

Revision 0

Revision description Draft

Prepared by Nicholas West

Reviewed by David Gerke

Approved by Christoff LeGrange

(name) (signature) (date)

Distributed to Niel Theron RVM Hydro Electric Power

(name) (organisation) (date)


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This page is intentionally blank.


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Contents

1. Introduction 1

2. Topography and surface drainage 5

3. Geotechnical Information 6

3.1 Augrabies Gneiss 6

3.2 Alluvium 8

4. Stormwater 8

4.1 Introduction 8

4.2 Project site drainage 9

4.2.1 Roads 9

4.2.2 Laydown areas, construction yards and spoil stockpile 9

4.2.3 Power chamber shafts 9

4.2.4 Water quality 9

4.3 Minor storm 10

4.4 Major storm 10

5. Conclusion 10

6. References 10

Appendices

A General Arrangement Drawings

B Design Rainfall Analysis

List of figures

Figure 1: Locality Plan (CES, 2015, p 24) 3

Figure 2.1: Digital terrain model of project area 5

Figure 3.1: Geology of the project area (from 1: 250 000 scale map) 7

Figure 3.2: Geology of the project area (from 1: 50 000 scale map) 7

Figure A.1: General layout of project infrastructure from diversion weir to tailrace outfall (CES, 2015, p 57) 14

Figure A.2: Layout of weir and offtake structure (CES, 2015, p 58) 15

Figure A.3: Layout of headpond, underground power chamber, tailrace tunnel and outfall (CES, 2015, p 59) 16

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Figure A.4: Position of the substation and proposed area for surplus spoil deposition (CES, 2015, p 60) 17


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1. Introduction

RVM1 Hydro Electric Power (Pty) Ltd (RVM Hydro) is proposing to construct a hydropower facility with a capacity of approximately 40MW near Augrabies in Northern Cape as shown in Figure 1.

The proposed hydropower station will consist of the following components:

A low diversion weir across the Orange River approximately 1.5 km upstream of the Augrabies Falls. An off‐take structure at the weir to facilitate diversion of water from the river.

A buried conduit – the headrace ‐ to convey water from the intake structure to the penstock head pond.

A head pond and power station intake structure ‐ forebay.

Vertical (or very steep) penstocks – pipes ‐ to transfer the water from the head pond to the power chamber, and to provide access & fresh air to the power chamber

An underground power chamber containing up to four Francis turbines.

An underground tailrace and outlet works to convey water from the power chamber back to the river channel.

Haul roads to facilitate access for construction and the removal of excavated material off site for disposal or re‐use.

A high voltage (HV) power line to evacuate the power from the power station to the national grid.

o Underground cable across portions 1/497 and Rem 498 (approximately 7.5 km); and

o Overhead power line across the river, over private land to the connection point (approximately 8 km).

A transformer yard and mini substation located below ground level at the head pond and a new substation.

Fencing as required for public safety.

Where existing roads do not exist for construction and maintenance purposes, new gravel access roads of 6m width will be constructed.

This report serves to outline the related surface and stormwater issues on the proposed site for the purposes of inclusion in the Environmental Management Plan.


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Figure 1: Locality Plan (CES, 2015, p 24)


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2. Topography and surface drainage

The following excerpt comes from CES, 2015, pp 14 – 15

“The majority of the project site is located in what can be classified as a “nearly flat plain”, with local relief of less than 5 metres and large areas nearly horizontal. However, near the north‐western end of the headrace, in the headpond area, this changes to a rolling plain with relatively low relief of between 5 and 100 metres and no steep slopes, and eventually to a low but steep escarpment of roughly 100 metres height at the site of the tailrace outfall. A number of shallow, ephemeral / episodic streams, which drain the higher‐lying terrain lying north‐east of the site, cross the water conduit route in a south‐western direction. These channels transport and deposit sandy alluvial material over parts of the route of the headrace.

The diversion weir, the approximate route of the headrace, site of the headpond and route of the tailrace, are shown on a digital terrain model in Figure 2.1, which shows the general topographic features of the project site, with spot heights in metres above mean sea level. The route of the headrace (black line adjacent to the secondary Orange River channel) indicates denuded

Figure 2.1: Digital terrain model of project area


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topography and a very slight surface gradient from the weir to near the headpond (refer to spot heights). Down‐slope from the headpond the surface slope to the re‐entrance into the Orange River gorge is steep. The plain north‐east of the site route gradually rises to higher elevations and steeper topography several hundred metres north‐east of the site.

The development of the drainage pattern of the Orange River in the vicinity of Augrabies Falls, which is roughly angular when viewed from above, has been influenced by two sets of steeply inclined geological master joint sets; one with an east‐west strike direction and the other with a north‐south strike direction. Joint sets lead to differential weathering rates. Lesser northeast‐ southwest and northwest‐southeast striking joint sets, as well as two geological faults, also contribute to the drainage pattern in the area. In the project site area in particular the preferential north‐south and east‐west drainage is, however, not immediately clear, with the exception of the place where the tailrace re‐joins the secondary Orange River channel. At that point an acute change in the direction of the erosion channel (a deep gorge) direction from west‐east to south‐north is apparent. However, in the main Orange River channel (a gorge) the pattern is more apparent.”

3. Geotechnical Information

The following excerpt comes from CES, 2015, pp 15 ‐ 17

“Rocks in the region are generally highly deformed metamorphosed sedimentary and volcanic rocks intruded by granitoids. The region is further characterised by numerous geological faults and shear zones. The area forms part of the Namaqua Metamorphic Province and lies within the Kakamas terrane of the Gordonia Sub‐province of the Namaqua Metamorphic Province. The published 1: 250 000 scale geological map, from which Figure 3.1 is extracted, indicates that the site is located on only one bedrock type, namely the Augrabies Gneiss, and that alluvial cover material occurs over the south‐eastern parts of the area.

On Figure 3.1 the route of the headrace and tailrace is shown as a red line. All infrastructural elements are located in the Augrabies Gneiss bedrock (purple polygons with deep red cross‐hatching), with alluvial cover (yellow polygons) at the south‐eastern end of the headrace. Other geological units in the area are: Riemvasmaak Gneiss (pink polygons); Omdraai Formation (gneiss and quartzite ‐ pale green polygons towards the east); and undifferentiated basic intrusive (gabbroic ‐ dark green polygon marked “Mga” towards the west).

3.1 Augrabies Gneiss

The Augrabies Gneiss is one of a number of intrusive rocks, which includes the Riemvasmaak Gneiss and basic intrusives, all with ages of between 1 300 million years and 1 000 million years. Mineralogically the Augrabies Gneiss consists of quartz, microcline and plagioclase with varying amounts of biotite and hornblende and with rare opaque minerals. The rock is a medium‐grained granitoid gneiss and has been partly re‐foliated, which lends a distinctive wavy pattern to the fabric and imparts a more massive character than is normal for foliated rock. The texture and fabric are remarkably uniform throughout the outcrop area, which underlies the majority of the south‐eastern parts of the Augrabies National Park and extends south‐eastwards outside the Park boundaries over a distance of roughly 8 kilometres in the direction of Augrabies village. The rock generally weathers to a greyish colour, is well exposed and forms the rock type into which the main Augrabies Falls and downstream canyon have been cut. An important feature of the


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Figure 3.1: Geology of the project area (from 1: 250 000 scale map)

Augrabies Gneiss is its tendency to form large exfoliation domes, the most well‐known of which is the “Moon Rock” occurring within the Park south of the Orange River.”

Figure 3.2: Geology of the project area (from 1: 50 000 scale map)


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3.2 Alluvium

With regard to alluvial cover over the bedrock, annotations on an unpublished 1: 50 000 scale geological field map (see Figure 3.2) indicate that the alluvium extends much further north‐westwards along the route of the headrace than indicated on the smaller scale (1: 250 000) published geological map, covering bedrock over the first 3.5 kilometres or so of the headrace route, and for about 1 kilometre south‐east of the site of the headpond area. The extent of the alluvial deposits is indicated on the larger scale map by a symbol similar to an elongated “m”.

Comparison of the route of the headrace with Google EarthTM images indicates that unconsolidated sedimentary materials appear to be covering the bedrock over some parts, whilst further along the route to the north‐west unconsolidated material appears to be absent, with bedrock (rock outcrop) dominating surface exposure. The sedimentary material may be relatively coarse sand – “gulley wash” or “hillwash” ‐ from the higher ground to the north‐east of the headrace route, or loose, fine‐grained alluvium deposited during flood events along the Orange River.

4. Stormwater

4.1 Introduction

The major elements of the infrastructure except the “downstream” sections of the powerlines by which power will be evacuated from the power houses will be constructed on three portions of land.

Orange River and its right‐bank riparian zone: The weir, offtake structure and the first few metres of the underground headrace will be constructed on this land.

Farm 497 ‐ Remainder (0) of Farm Waterval: Infrastructure to be constructed on this portion of land will comprise:

o The first 3km or so of the underground headrace.

o Approximately 6km of underground power line

o Approximately 6km of access road.

Farm 498 – Portion 1 of Farm Riemvasmaak: Infrastructure to be constructed on this portion of land will comprise:

o The downstream 1.6km or so of the underground headrace;

o The headpond;

o The penstocks;

o The underground powerhouse and electrical infrastructure;

o The tunnelled tailrace and tailrace outfall into the Orange River;

o About 2km of the underground transmission line;

o About 2km of the access road;

o An access road or haulage way to the tailrace outfall point.


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The section of the underground powerline that runs south‐east from the site of the weir and offtake structure (see Figure 3.3) crosses Waterval 497/0 at the south‐eastern boundary, where it enters a substation on Portion 1 of Farm 492. Thereafter the power line is above ground, and crosses a number of parcels of private land, and the Orange River, before it is connected to either an existing 132kV Eskom power line between Renosterkop and Blouputs or directly at the Renosterkop substation. The 100 year return period flood line has been mapped for the Orange River as part of the development of the project. The majority of structures comprising the works are located outside this flood extent. The 100 year return period flood lines have not been mapped for local catchments.

4.2 Project site drainage

4.2.1 Roads

The majority of the access roads constructed for the Project will be gravel roads. To assist with the stormwater run‐off, these gravel roads should typically be graded and shaped with a 3% crossfall back into the slope, allowing stormwater to be channelled in a controlled manner towards the natural drainage lines and to assist with any surface water sheetflow on the site.

Where any proposed roads, intersect the natural, defined drainage lines, it is suggested that either suitably sized pipe culverts or drive through causeways are installed/constructed and should take into account the hydrology criteria for a selected major storm as outlined in Section 4.4.

4.2.2 Laydown areas, construction yards and spoil stockpile

A swale that is shaped and erosion lined where necessary should be constructed around laydown areas, construction yards and the spoil stockpile to intercept stormwater drainage approaching these area. The swale should intercept and direct water where possible away from these construction areas and towards the existing drainage lines. This swale should have a minimum slope of 0.2%.

The laydown areas and construction yards should be sloped at a minimum of 2% to allow surface stormwater run‐off to migrate away. Stormwater will run into the swale located at the toe and adjacent to the laydown area/construction yard. Where the swale meets the natural drainage lines, erosion protection may be required.

4.2.3 Power chamber shafts

Natural stormwater run‐off emanating of the higher lying ground above the power chamber, shafts should be directed, with the help of table drains, away from the these structures into the natural drainage lines with slope protection measures employed to control/minimise erosion where required.

4.2.4 Water quality

Water quality requirements associated with drainage works must comply with the requirements of the CEMP.


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4.3 Minor storm

The minor storm design period should be used to determine the size of the earth drainage channels. A return period of 5 years is applicable which approximates to an average intensity of 26.1 mm/hour.

4.4 Major storm

The major storm occurrence, i.e. 50 year and 100 year return periods, should be used to calculate culverts in defined drainage lines and to determine flood levels where necessary. Intensities for each occurrence are as follows; 50 year – 50.7 mm/hour and 100 year – 59.2 mm/hour respectively.

5. Conclusion

It should be noted that an indicative site layout and project description has been produced based on the infrastructure described in the ‘Draft Environmental Impact Report’. Further, re‐evaluation/upgrading of this preliminary design will be required to ensure the alignment and sizing of infrastructure is compatible with the environmental scoping criteria when the site layout and details have been finalised.

6. References

EOH Coastal & Environmental Services (CES), 2015, Environmental Impact Assessment Report, April


Appendices




A General Arrangement Drawings

RVM Hydro Electric Project ‐ Stormwater Management Plan Revision No: 0 ConsultDM no. 7 May 2015

Figure A.1: General layout of project infrastructure from diversion weir to tailrace outfall (CES, 2015, p 57)


Figure A.2: Layout of weir and offtake structure (CES, 2015, p 58)


Figure A.3: Layout of headpond, underground power chamber, tailrace tunnel and outfall (CES, 2015, p 59)


Figure A.4: Position of the substation and proposed area for surplus spoil deposition (CES, 2015, p 60)




B Design Rainfall Analysis




Design Rainfall in South Africa: Ver 3 (July 2012)

Data extracted from Daily Rainfall Estimate Database File

Gridded values of all points within the specified block

Latitude Longitude MAP Altitude Duration Return Period (years)

(°) (') (°) (') (mm) (m) (h) 5 5L 5U 50 50L 50U 100 100L 100U

28 32 20 18 120 600 1 26.1 18.5 33.9 50.7 34.1 68.4 59.2 39 81.2 28 32 20 19 118 600 1 26.1 18.4 33.8 50.5 33.9 68.3 59 38.8 81 28 32 20 20 132 675 1 26.5 18.8 34.2 51.3 34.8 69 59.9 39.7 81.9 28 32 20 21 123 650 1 26.2 18.5 33.9 50.8 34.2 68.5 59.3 39.1 81.3 28 32 20 22 127 675 1 26.3 18.7 34 51 34.4 68.7 59.6 39.3 81.6 28 33 20 18 109 575 1 25.8 18.1 33.5 50 33.4 67.8 58.4 38.2 80.4 28 33 20 19 127 625 1 26.3 18.6 34 51 34.4 68.7 59.6 39.3 81.6 28 33 20 20 118 600 1 26 18.3 33.8 50.5 33.8 68.2 58.9 38.7 81 28 33 20 21 126 650 1 26.2 18.6 33.9 50.9 34.3 68.6 59.4 39.2 81.4 28 33 20 22 129 675 1 26.3 18.7 34 51.1 34.5 68.8 59.6 39.4 81.6 28 34 20 18 122 625 1 26.1 18.5 33.9 50.7 34.1 68.4 59.2 39 81.2 28 34 20 19 122 625 1 26.1 18.5 33.8 50.6 34.1 68.4 59.1 38.9 81.1 28 34 20 20 128 625 1 26.3 18.6 34 51 34.4 68.7 59.5 39.3 81.5 28 34 20 21 125 625 1 26.2 18.5 33.9 50.8 34.2 68.5 59.3 39.1 81.3 28 34 20 22 126 650 1 26.2 18.6 33.9 50.8 34.2 68.6 59.3 39.1 81.4 28 35 20 18 107 600 1 25.6 18 33.4 49.8 33.1 67.5 58.1 37.9 80.1 28 35 20 19 113 600 1 25.8 18.1 33.6 50.1 33.4 67.9 58.5 38.2 80.5 28 35 20 20 127 625 1 26.2 18.6 34 50.9 34.2 68.6 59.4 39.2 81.4 28 35 20 21 128 625 1 26.2 18.6 34 50.9 34.3 68.6 59.4 39.2 81.4 28 35 20 22 125 625 1 26.1 18.5 33.9 50.7 34.1 68.5 59.2 39 81.2 28 36 20 18 115 625 1 25.9 18.2 33.6 50.2 33.5 67.9 58.6 38.3 80.6 28 36 20 19 120 625 1 26 18.3 33.7 50.4 33.8 68.2 58.9 38.7 80.9 28 36 20 20 123 625 1 26.1 18.4 33.8 50.6 34 68.3 59.1 38.8 81.1 28 36 20 21 126 625 1 26.2 18.5 33.9 50.7 34.1 68.5 59.2 39 81.3 28 36 20 22 127 625 1 26.2 18.5 33.9 50.8 34.2 68.5 59.3 39.1 81.3



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RVM Hydro Electric Project - CESNET 1 Hydro Electric Power...Prepared by Hydro‐Electric Corporation ABN48 072 377 158 t/a Entura 89 Cambridge Park Drive, Cambridge TAS 7170 Australia