Hydrological Assessment of the Proposed Haga Haga Wind Energy Facility

HYDROLOGICAL ASSESSMENT OF THE PROPOSED HAGA HAGA WIND ENERGY FACILITY

Project No. SAS-06

Version 3

July 2018

HYDROLOGIC CONSULTING

CONSULTING HYDROLOGISTS

email: [email protected] | phone: +27 72 239 0974 HYDROLOGICAL ASSESSMENT OF THE PROPOSED HAGA HAGA WIND ENERGY FACILITY

Prepared For

Scientific Aquatic Services CC

Scientific Aquatic Services CC CC Reg No 2003/078943/23 Vat Reg. No. 4020235273 PO Box 751779 Gardenview 2047 Tel: 011 616 7893 Fax: 086 724 3132 E-mail: [email protected]

Prepared By

Hydrologic Consulting (Pty) Ltd

Version 3

Project No. SAS-06

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TABLE OF CONTENTS 1 INTRODUCTION ...... 1

1.1 BACKGROUND ...... 1 1.2 SCOPE OF WORK ...... 1 1.3 REGIONAL SETTING AND SITE LAYOUT ...... 1

2 BASELINE INFORMATION ...... 4

2.1 RAINFALL ...... 4 2.2 1-DAY DESIGN RAINFALL DEPTHS ...... 6 2.3 EVAPORATION ...... 6 2.4 AVERAGE CLIMATE ...... 7 2.5 TOPOGRAPHY AND SLOPES ...... 8 2.6 HYDROLOGY ...... 8 2.7 SOILS, VEGETATION AND LAND-COVER ...... 10

3 STORMWATER AND EROSION CONTROL MANAGEMENT PLAN ...... 13

3.1 CLEAN AND DIRTY AREAS ...... 13 3.1.1 IDENTIFICATION OF SENSITIVE INFRASTRUCTURE ...... 14 3.2 CONSTRUCTION PHASE- MANAGEMENT PLAN ...... 16 3.2.1 REVIEW OF POTENTIALLY SENSITIVE INFRASTRUCTURE...... 17 3.2.2 SITE-SPECIFIC MANAGEMENT PLANS ...... 22 3.2.3 GENERIC MANAGEMENT PLANS ...... 22 3.2.4 STORMWATER MANAGEMENT AND EROSION CONTROL ...... 23 3.2.5 RIVER CROSSINGS ...... 26 3.3 OPERATIONAL PHASE- MANAGEMENT PLAN ...... 27

4 CONCLUSIONS AND RECOMMENDATIONS ...... 28

5 REFERENCES ...... 29

APPENDIX A – STORMWATER CALCULATIONS ...... 30

A.1 MODEL CHOICE ...... 30 A.2 MODEL SETUP ...... 30 A.2.1 DESIGN STORM ...... 30 A.2.2 MODEL PARAMETERISATION ...... 30 A.3 MODEL RUN ...... 30

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LIST OF FIGURES

FIGURE 1-1: REGIONAL SETTING ...... 2 FIGURE 1-2: SITE LAYOUT ...... 3 FIGURE 2-1: WEATHER STATIONS AND MEAN ANNUAL PRECIPITATION ...... 5 FIGURE 2-2: AVERAGE MONTHLY CLIMATE FOR THE SITE...... 7 FIGURE 2-3: TOPOGRAPHY AND HYDROLOGY ...... 9 FIGURE 2-4: SOILS AND VEGETATION ...... 11 FIGURE 2-5: LAND-COVER ...... 12 FIGURE 3-1: FLOW PATHS AND POTENTIALLY SENSITIVE INFRASTRUCTURE ...... 15 FIGURE 3-2: DETAILED ASSESSMENT OF TURBINES 01, 02, 14 & 17 ...... 18 FIGURE 3-3: DETAILED ASSESSMENT OF TURBINES 20, 26, 29 & 33 ...... 19 FIGURE 3-4: DETAILED ASSESSMENT OF TURBINES 34, 36, 39 & 41 ...... 20 FIGURE 3-5: DETAILED ASSESSMENT OF TURBINES 42 & LAYDOWN AREA ...... 21 FIGURE 3-6: GENERIC EXAMPLE STORMWATER/EROSION CONTROL MANAGEMENT...... 23 FIGURE 3-7: TYPICAL BERM AND CHANNEL FOR STORMWATER/EROSION MANAGEMENT SYSTEM ...... 24 FIGURE 3-8: TYPICAL SILT FENCE (AFTER ENVIRONMENT PROTECTION AGENCY) ...... 25

LIST OF TABLES

TABLE 2-1: AVERAGE MONTHLY RAINFALL DISTRIBUTION (LYNCH, 2004) ...... 4 TABLE 2-2: 24-HOUR STORM DEPTH ...... 6 TABLE 2-3: MONTHLY POTENTIAL EVAPOTRANSPIRATION DISTRIBUTION (SCHULZE AND LYNCH, 2006) .... 7

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EXECUTIVE SUMMARY

Hydrologic Consulting (Pty) Ltd has been appointed by Scientific Aquatic Services CC, to undertake a hydrological assessment for the proposed Haga Haga Wind Farm. The project consists of 42 wind turbines, to be installed atop various hills near Haga Haga, within the Great Kai Local Municipality, approximately 45km north-east of East London in the Eastern Cape Province of South Africa. Additional infrastructure in the form of a Substation, Office and Laydown area as well as linear infrastructure (overhead powerline, electrical underground cables and roads) are also proposed. This hydrological assessment has been undertaken to inform both Environmental and Water Authorisation processes.

The scope of work in the hydrological assessment included the following:

• Baseline Assessment – sourcing of baseline climatic data to be used in hydrological calculations. This included the interrogation of rainfall data (including site specific design rainfall), evaporation, soils, vegetation, land-cover, as well as a regional and local hydrological assessment;

• Conceptual Stormwater and Erosion Control Management Plan – development of both construction and operational management principles which can be used to ensure the impact of the proposed operation on receiving water resources is kept to a minimum. This includes a buffer approach adopted for the rivers traversing the site; and

• Technical Report – detailing the achieved scope of work.

Baseline information including average rainfall data, depth-duration-frequency design rainfall estimates, evaporation data, soils, vegetation and land-cover information, as well as both regional and local hydrological characteristics have been considered for the proposed Haga Haga Wind Energy Facility in the Eastern Cape. The results of this baseline assessment indicate that the proposed site is located in a medium to high rainfall, low to medium evaporation region of South Africa, with moderate to mild slopes.

The impact of the proposed project on surface water resources during both construction and operational phases was assessed and found to be limited, particularly during the operational phase. During the construction phase, there is increased potential for soil erosion if stormwater is not correctly managed due to the removal of vegetation and subsequent exposure of the soil surface to rainfall. Numerous management principles were developed for both the construction and operational phases of the project. The most significant of these is the proposed construction of a berm/channel surrounding each of the 42 disturbed turbine areas and the Substation, Office and Laydown area which is routed to a sediment control area (e.g. a silt trap or silt fence). This is to enable the settling out of sediment associated with these dirty areas. Erosion control can also likely be achieved using a silt fence surrounding dirty areas as an alternative to a berm/channel draining to a silt fence, since runoff rates and volumes off the turbine area are low. The Substation, Office and Laydown area, however, requires a berm/channel and to route runoff from the upslope clean water area between the Construction Storage and Office areas

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These management measures and principles have been developed to ensure the impact of the proposed operation on receiving water resources is kept to a minimum. It is consequently likely that the significance of the impact on the surface water (hydrological) environment would be low, assuming the management measures and principles outlined in this report are adhered to.

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HYDROLOGICAL ASSESSMENT OF THE PROPOSED HAGA HAGA WIND ENERGY FACILITY

1 INTRODUCTION

1.1 BACKGROUND

Hydrologic Consulting (Pty) Ltd has been appointed by Scientific Aquatic Services CC, to undertake a hydrological assessment for the proposed Haga Haga Wind Energy Facility. The project consists of 42 wind turbines, to be installed atop various hills near Haga Haga, within the Great Kai Local Municipality, approximately 45km north-east of East London in the Eastern Cape Province of South Africa. Additional infrastructure in the form of a Substation, Office and Laydown area as well as linear infrastructure (overhead powerline, electrical underground cables and roads) are also proposed. This hydrological assessment has been undertaken to inform both environmental and water authorisation processes.

1.2 SCOPE OF WORK

The scope of work included the following:

• Baseline Assessment – sourcing of baseline climatic data to be used in hydrological calculations. This involved the interrogation of rainfall data (including site specific design rainfall), evaporation, soils, vegetation, land-cover, as well as a regional and local hydrological assessment;

• Technical Report – detailing the achieved scope of work.

1.3 REGIONAL SETTING AND SITE LAYOUT

The proposed wind farm boundary is centred at approximately 28° 13' 15 "E and 32° 41' 05" S. Figure 1-1 illustrates the regional setting of the project (hereafter referred to as the site). The proposed site layout is presented in Figure 1-2 and includes:

• 42 wind turbines; • 42 crane pads and areas of hardstanding (adjacent the turbines); • 1 office, laydown and substation area comprised of four blocks for a substation, construction storage, office and temporary laydown area ; and • Linear infrastructure in the form of site roads (both new and existing), overhead powerlines and underground electrical cables.

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Figure 1-1 Regional Setting -80000 -75000 -70000 -65000 Legend ± !> Turbine Area of Interest

Substation, Office and Laydown Area

Road (Provincial)

Road (New)

Road (Upgrade)

Tracks 0 0 0 0 0 0 5 5

1 1 Electrical Underground Cable 6 6 3 3 - - Overhead Powerline 0 0 0 0 0 0 0 0 2 2 6 6 3 3 - -

0 1 2 Kilometers Scale: 1:62,500 @ A3

Projection: Transverse Mercator Datum: Hartebeeshoek, LO29

Figure 1-2

Layout

0 0 Hydrologic Consulting (Pty) Ltd 0 0 0 0 5 5

2 2 Consulting Hydrologists 6 6 3 3 - - I! +27 72 239 0974 I- [email protected] I" www.hydrologic.za.com

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2 BASELINE INFORMATION

Baseline information in this section includes discussions on average rainfall, design event rainfall, evaporation, topography, slopes, soils, vegetation, land-cover as well as both regional and local catchment hydrology.

2.1 RAINFALL

Various weather stations managed by both the South African Weather Services (SAWS) and the DWS were considered in this project. These, together with their proximity to site can be seen in Figure 2-1 which illustrates the rainfall variability in the greater area and shows that mean annual precipitation (MAP) increases towards the coast and towards the north-east. The MAP of the site varies between approximately 800mm and 1150mm and is a medium to high rainfall area in comparison to other areas in South Africa.

Various rainfall stations are present in the area about the site, the closest of which is SAWS station 81013 W. Data for this station was, however, not readily available and alternative rainfall data was considered. Lynch (2004) which was used to illustrate the MAP as per Figure 2-1, and was also used to define average monthly rainfall. Lynch (2004) includes details on the development of a raster database of monthly rainfall data for Southern Africa. The resultant raster database utilises a geographically weighted regression which takes account of factors including latitude, longitude, altitude, slope and distance from the sea, when interpolating data from rainfall stations located throughout Southern Africa.

For the purposes of the study, the rainfall values from the centre of the site (28° 13' 15 "E and 32° 41' 05" S) as indicated in Lynch (2004) have been used and are presented in Table 2-1.

TABLE 2-1: AVERAGE MONTHLY RAINFALL DISTRIBUTION (LYNCH, 2004)

Month Rainfall (mm) Jan 90 Feb 98 Mar 115 Apr 76 May 45 Jun 32 Jul 33 Aug 42 Sep 78 Oct 111 Nov 111 Dec 87 Total 918

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Hydrologic Consulting (Pty) Ltd

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2.2 1-DAY DESIGN RAINFALL DEPTHS

For the development of a storm water and erosion control management plan, design rainfall is the most important rainfall variable to consider as it is the driver behind high runoff events when potential erosion is likely to highest.

Design storm estimates for various recurrence intervals (RI) and storm durations were sourced from the Design Rainfall Estimation Software for South Africa (DRESSA), developed by the University of Natal in 2002 as part of a WRC project K5/1060 (Smithers and Schulze, 2002). This method uses a Regional L- Moment Algorithm (RLMA) in conjunction with a Scale Invariance approach to provide site specific estimates of design rainfall (depth, duration and frequency), based on surrounding station records. WRC Report No. K5/1060 (WRC, 2002) provides more detail on the verification and validation of the method.

The design rainfall estimates (24-hour storm) using the above technique have been compared to that obtained in TR102 (Design Rainfall Depths at Selected Stations in South Africa) for the 0081013 W (Mooiplaas) rainfall station, with the DRESSA results used for this study since they are both site-specific and more conservative (i.e. larger).

TABLE 2-2: 24-HOUR STORM DEPTH

Rainfall Depth (24 hour) Recurrence (mm) Interval DRESSA TR102 (Years) (Smithers/Schulze)* 2 109 92 5 161 137 10 201 171 20 245 208 50 309 263 100 365 310 200 426 362 *Estimates were sourced for the centre of the site

It is important to note, that no allowances for climate change have been made. A risk analysis using the expected life of a structure or process will indicate the relevance of considering climate change (i.e. as the expected life increases the influence of climate change increases).

2.3 EVAPORATION

Evaporation data was sourced from the South African Atlas of Climatology and Agrohydrology (Schulze and Lynch, 2006) in the form of A-Pan equivalent potential evapotranspiration. The average monthly evaporation distribution is presented in Table 2-3 and shows the site has an annual potential evapotranspiration of 1613mm which is low to medium in comparison to other areas in South Africa.

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TABLE 2-3: MONTHLY POTENTIAL EVAPOTRANSPIRATION DISTRIBUTION (SCHULZE AND LYNCH, 2006)

Month Potential Evapotranspiration (mm) Jan 176 Feb 150 Mar 136 Apr 117 May 111 +Jun 102 Jul 99 Aug 119 Sep 125 Oct 146 Nov 150 Dec 182 Total 1613

2.4 AVERAGE CLIMATE

The average climate for the site is presented in Figure 2-2 using the outcome of the investigation into rainfall and evaporation for the site. While evaporation is showing as greatly exceed rainfall, this is representative of the maximum potential evapotranspiration that could occur assuming no limitations are placed on evaporative demand. The combination of rainfall and temperature result in a humid sub- tropical climate according to the Köppen climate classification.

Rainfall (mm) Potential Evapotranspration (mm) Max Temp (°C) Min Temp (°C) 200 30 *South African Atlas of Climatology and Agrohydrology Used for Temperature 180 25

160

(mm)

C) ° 140 ( 20 120

100 15

80 Temperature 10

Rainfall/Evaporation 60

40 5 20

0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

FIGURE 2-2: AVERAGE MONTHLY CLIMATE FOR THE SITE

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2.5 TOPOGRAPHY AND SLOPES

In assessing the topography and site slopes, a single elevation dataset was used in the form the 30m SRTM1 (Shuttle Radar and Topography Mission) digital elevation model (DEM) for the site and surrounds. The elevation data in combination with derived site slopes and regional hydrology is illustrated in Figure 2-3.

General elevations range from approximately 400m AMSL in the north-west of the site to approximately 100m AMSL in areas nearer the coast. The proposed turbines are, however, positioned on hilltops with the lowest turbine located at approximately 150m AMSL.

Site slopes vary considerably, from flat valleys to steep hills. The hills on which the turbines are located are associated with steeper topography with slopes above 10% in most instances.

2.6 HYDROLOGY

Figure 2-3 illustrates the topographical and hydrological setting of the proposed project, while Figure 2-1 presents the river network of the greater region. The site is almost entirely contained by quaternary catchment R30A with a small portion of the northern edge of the site located in quaternary S70F. For the purposes of this study, the site can be considered fully contained within quaternary R30A since no infrastructure is proposed within quaternary S70F.

Various rivers drain the site’s proposed infrastructure with a few primary rivers noted. These include named perennial rivers such as the Nyarha, Haga Haga, Quko, Kugwevvana and Kumqotwane rivers. The Gugura River drains the northern edge of the site (located in quaternary S70F) to the Groot-Kei River which is the dominant river in the region. Aside from the named perennial rivers, various other perennial rivers are noted while the sites non-perennial rivers result in an overall dense river network. All rivers on the site drain to the Indian Ocean which is located approximately 2km away from the south-eastern border of the site (at its closest).

In considering surface water features other than rivers, numerous small dams are indicated as being present on the site when considering the 1:50,000 topographical map data for the area. Wetlands as defined by the National Freshwater Ecosystems Priority Areas (NFEPA, 2011) dataset for South Africa are present, primarily in association with dams on site. A wetland survey was undertaken by Scientific Aquatic Services to define the extent of wetlands on site and should be consulted for more detail.,

The bulk of infrastructure on site is located along the hilltops, and consequently there aren’t any dams within 32m of proposed turbines (or associated crane pads). Linear infrastructure on the site does however come within close proximity to defined dams in a few instances (<10m away). Proximity of infrastructure to rivers is discussed in Section 3.

1 Data available from the U.S. Geological Survey

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E-80000 -75000 -70000 -65000 AN GUGURA M Legend LI M G R O Area of Interest 0 0 O 6 20 T 2 0 - 4 K 3 E IR ! Turbine ± GU I > GURA V IE 0 G 32 R S70F R

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0 0 Wetlands (NFEPA , 2011) 0 0 0 0 0 0

2 33 2 6 6 3 3

- 1 - 34 2 !> 0 Quaternary Catchments 20

!> K 35 U 37 M Indian Ocean 36 Q R30A 38 !> O

N !> !> T Y W Elevation (SRTM30) !> O A 40

K R A

1 6 U N H 8 0 0 41 Value ! Q E A >

0 42 !> 4 High : 400 !> Low : 0

SRTM30 DERIVED SLOPE (%)

0 1 2 Kilometers Scale: 1:62,500 @ A3 0 8 0

0 1 0 8 0 0 0 0 5 5 Projection: Transverse Mercator 2 2 6 6

3 3 Datum: Hartebeeshoek, LO29 - -

Figure 2-3 H 1 A 6 G 0 A- HA GA Hydrology, Topography A RI R VE < 3 and Slope (%)

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2.7 SOILS, VEGETATION AND LAND-COVER

According to the high-level soils data included in the Water Resources of South Africa 2012 (WR2012) study (Bailey and Pitman, 2015), soils on the site are classified as Sandy Clay Loams. In considering the more detailed Soil Conservation Service for South Africa (SCS-SA) dataset, a low to moderately low runoff potential classification is noted for the site (i.e. SCS-SA group A/B soil).

The natural vegetation of the site is mostly that of Albany Dune Strandveld and Bhisho Thornveld (as defined by the SA Vegetation Atlas SANBI, 2012) with current land-cover predominantly comprised of thicket/dense bush and grasslands. Cultivated commercial annual crops (non-pivot) are noted to the south with a single stand of plantations/woodlots noted in the north-east of the site.

The distributions of the SCS soil types and natural vegetation are illustrated in Figure 2-4 while Figure 2-5 presents the land-cover of the site according to the Department of Environmental Affairs (DEA) 2014 dataset.

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-80000 -70000 Legend ± Area of Interest !> Turbine

Road (Provincial)

SANBI Vegetation Atlas (2012)

Albany Coastal Belt

1 2 Albany Dune Strandveld !> !> 3 4 Bhisho Thornveld 5 !> !> 6 !> 7 9 8 !> Buffels Thicket

31 !> !> !> 10 11 Cape Coastal Lagoons !> 32 !> 12 !> !> 13 Eastern Valley Bushveld !> 14 15 !> 17 ! 39 > !> Southern Mistbelt Forest 19 18 !> !> 20 !> !> 23 Transkei Coastal Belt 22 !> 16 !> !> 24 !> SCS Soils Runoff Potential 21 !> 26 25 !> ! A - Low Runoff Potential !> 27 > !> 28 A/B 29 !> 30 ! B - Moderately Low Runoff Potential > !> B/C 0 0 0 0 0 0

0 0 C - Moderately High Runoff Potential 2 33 2 6 6 3 3 - 34 !> - C/D !> 35 36 37 38 !> Indian Ocean !> !> !> 40 !> 41 42 !> !>

0 1 2 Kilometers Scale: 1:200,000 @ A3

Projection: Transverse Mercator Datum: Hartebeeshoek, LO29

Figure 2-4

Soil and Vegetation

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-80000 -70000 Legend ± Area of Interest !> Turbine

Road (Provincial)

Indigenous Forest

Thicket /Dense Bush

1 2 Woodlan/Open Bush !> !> 3 4 Low Shrubland 5 !> !> 6 !> 7 9 8 !> Plantations / Woodlots

31 !> !> !> 10 11 Commercial Annual Crops Non-Pivot 32 !> !> !> !> 13 12 Commercial Annual Crops Pivot !> 14 15 !> 17 !> !> 39 Commercial Permanent Orchards 19 18 !> !> 20 !> !> 23 Cultivated Subsistence Crops 22 !> 16 !> !> 24 !> Settlements 21 !> 26 25 !> Wetlands ! !> 27 > !> 28 Grasslands 29 !> 30 Mines ! > !> Waterbodies 0 0 0 0

0 0 Bare Ground 0 0

2 33 2 6 6 3 3 - 34 !> - Degraded !> 35 36 37 38 !> !> !> !> 40 !> 41 42 !> !>

0 1 2 Kilometers Scale: 1:200,000 @ A3

Projection: Transverse Mercator Datum: Hartebeeshoek, LO29

Figure 2-5

Land-Cover

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3 STORMWATER AND EROSION CONTROL MANAGEMENT PLAN

The proposed project will alter the natural surface water environment, particularly during the construction phase, thereby affecting the generation of stormwater and the associated potential for erosion. It is therefore important to identify the impact the proposed wind farm will have on stormwater production and manage this water accordingly. Volumes of stormwater generated are expected to increase due to the establishment of the wind turbines through the replacement of natural vegetation with areas of hardstanding. The quality of the stormwater generated is also expected to be affected, particularly during the construction phase. The purpose of this section is to produce a stormwater and erosion control management plan by which clean and dirty water generating areas are firstly identified and then managed appropriately for both the construction and operation phases.

The aim of this management plan is to consider best practices as presented in various guidelines in South Africa and beyond. These include:

• Government Notice 704 (Government Gazette 20118 of June 1999), which while it focuses on mining, includes some important principles by which clean and dirty water producing areas can be managed effectively; • Department of Water and Sanitation (DWS) Best Practice Guideline G1 for Stormwater Management; • A paper presented by Ferreria and Waywood at the 2009 International Mine Water Conference (Ferreria and Waywood, 2009), references the standards used by the Province of British Columbia (1996). This paper included some valuable concepts, particularly focused on sediment control; • Landcom Soils and Construction, Volume 1, 4th edition from 2004 (otherwise known as the Blue Book) has been used widely in the South African context in providing practical recommendations regarding the management of stormwater and associated erosion controls; and • The South African Roads Agency Limited (SANRAL) 6’th edition Drainage Manual (2013) provides some valuable insight specific to the construction and operation of various roads, a network of which will be developed as part of this proposed project.

3.1 CLEAN AND DIRTY AREAS

The following definitions are important to the development of a stormwater and erosion control management plan:

• Dirty Area – this refers to the area on site which will be disturbed due the construction of the wind turbines and associated infrastructure. These areas are not expected to be ‘chemically’ dirty, and are instead anticipated to be associated with areas prone to erosion by rainfall due to the exposure of soil caused by the stripping away of vegetation. Without mitigation, disturbed areas will likely result in a higher proportion of Total Suspended Soils (TSS) being mobilised and entering rivers (thereby degrading water quality), compared to undisturbed areas. Sediment

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control is consequently necessary and is commonly achieved through the inclusion of stormwater settling facilities (also known as silt traps) or through the use of silt fences. • Clean Area – This refers to the natural areas upslope or upstream of dirty areas, where runoff, if unimpeded, would run onto dirty areas.

3.1.1 IDENTIFICATION OF SENSITIVE INFRASTRUCTURE

To provide an approach to stormwater and erosion control management associated with the proposed infrastructure on site, it was necessary to first determine the upstream or upslope contributing area passing near to or through either a turbine area (including crane pad) or the Substation, Office and Laydown area. Linear infrastructure was not considered in this section and is instead referenced in Section 3.2.5. In calculating the contributing area, the ‘clean area’ component of the study could be defined. For the purposes of calculating the contributing area upstream or upslope of affected infrastructure, the SRTM30 DEM for the site was processed with the following classification:

• 1km2 contributing area flow path – for upstream/upslope contributing areas equal to or more than 1km2; • 0.5km2 contributing area flow path – for upstream/upslope contributing areas equal to or more than 0.5km2; and • 0.25km2 contributing area flow path– for upstream/upslope contributing areas equal to or more than 0.25km2.

The ‘contributing area flow paths’ were derived from SRTM30 data and indicate those areas which have a contributing area (or flow accumulation area) of equal to or more than the area specified. The reason for this classification was to determine potentially sensitive infrastructure requiring a more tailored management approach other than the generic management approach to be discussed in Section 3.2.3. This is because there is greater need for formalised clean area diversions where contributing areas exceed a threshold area (defined as equal to or greater than 0.25km2 for this study).

The 1km2, 0.5km2 and 0.25km2 contributing area classes were ‘buffered’ with a 100m, 50m and 25m buffer, respectively. Rivers on site were likewise buffered by both 32m (applicable to NEMA, 1998) and 100m (applicable to GN704, 1998). The purpose of this buffering approach is to both tie in with existing guidance (e.g. NEMA in the case of the 32m buffer) as well as to present a weighted approach to the uncertainty regarding flow accumulation on the site and the higher potential peak flows and volumes that can arise from larger area. This uncertainty is due to the coarse nature of the SRTM30 data, which has a cell size approximating 30m (or more specially, 28.5m). The minimum buffer distance of 25m approximates the 28.5m SRTM30 cell size for the site, thereby avoiding some of the potential accuracy errors caused by using a coarse DEM by highlighting potentially sensitive infrastructure due to its proximity to a defined flow path. The larger flow path buffers of 50m and 100m are indicative of the greater impact the respective contributing area flow paths may have and the weighted buffer approach used in this regard (relating to risk). Figure 3-1 presents the results of the flow path and river buffering approach used to identify potentially sensitive infrastructure.

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-80000 -75000 -70000 -65000 Legend

!? Turbine/Cranepad (No Intersect) ± ?! Turbine/Cranepad (100m Intersect) Area of Interest

"J River Crossing (Linear Infrastructure) 1 2 Substation, Office and Laydown Area

3 4 Road (Provincial) 5 6

0 0 Road (New) 0 0

0 7 9 0 5 8 5 1 1 6 6 3 3 - - 31 10 Road (Upgrade) 11 32 12 Overhead Powerline 13 14 15 17 Electrical Underground Cables 39 19 18 River (50K Topo) 20 23 22 >1 sq.km Contributing Area 16 24

21 >0.5 sq.km Contributing Area 26 25 >0.25 sq.km Contributing Area 27

28 Flow Path Buffer - Contributing Area 29 25m Buffer - (>0.25sq.km) 30 50m Buffer - (>0.5sq.km)

100m Buffer - (>1sq.km) 0 0 0 0 0 0 0 0

2 2 32m River Buffer (50K Topo)

6 33 6 3 3 - - 34 100m River Buffer (50K Topo)

35 36 37 38

40 41 0 1 2 Kilometers 42 Scale: 1:52,500 @ A3 Projection: Transverse Mercator Datum: Hartebeeshoek, LO29

Figure 3-1

Flow Paths and Potentially Sensitive Infrastructure

Hydrologic Consulting (Pty) Ltd Consulting Hydrologists

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It should be noted that the 1:50,000 topographical map rivers were assumed to be accurate and were ‘burnt’ into the SRTM30 data to ensure the resulting flow paths matched the river network. This approach supersedes the SRTM30 derived drainage that may otherwise differ from the 1;50,000 topographical map rivers. The subsequent buffering of the contributing area flow paths is also presented in the figure (with the heading ‘Flow Path Buffer - Contributing Area’). Thirteen turbine areas and the Substation, Office and Laydown area were subsequently identified as ‘potentially sensitive infrastructure’ as they intersected one or more of the aforementioned buffers. These areas are discussed in more detail in Section 3.2.1.

In considering the river buffers, it was interesting to note that due to the high drainage density, the site’s 1:50,000 topographical map rivers started well before the 0.25km2 contributing area flow paths. This makes the 1:50,000 topographical map rivers and their associated buffers the most relevant when identifying sensitive infrastructure.

3.2 CONSTRUCTION PHASE- MANAGEMENT PLAN

During construction, it is understood that for each of the proposed wind turbines, an area of approximately 40m x 97m or 3880m2 including crane pads will be cleared of vegetation and followed by light excavation. A concrete foundation and slab will then be poured, onto which the turbine will be fixed. The Substation, Office and Laydown area presented in Figure 3-1 also requires clearing/levelling and is 36,000m2 (3.6ha) in size. For the purposes of this study, the aforementioned areas are all considered ‘dirty areas’. Sediment control is often necessary where vegetation is stripped away, exposing areas prone to erosion by rainfall. Control of sediment is commonly achieved through the inclusion of stormwater settling facilities or silt fences. Silt laden waters (with a high TSS load) require a slowing down of the water for the suspended solids to settle. The following principles should be adhered to, as taken from a combination of the various guidelines previously listed:

• All excavation/construction vehicles such as excavators and cranes should be in good condition and inspected regularly to ensure there are no diesel/oil spills which will negatively impact the receiving environment. • Construction activities should ideally not take place within the 1:100 year flood-line (if available) or within a horizontal distance of 100m from any watercourse or wetland, apart from linear infrastructure which is required to traverse watercourses, such as roads and flood compatible infrastructure such as electrical pylons. • Without defined flood-lines, the 32m and 100m buffers serve as an indicative distance to protect against flooding with the 100m river buffer the preferred exclusion zone (defined by GN704) and the 32m buffer a required exclusion zone defined by NEMA (1998). • Clearing of vegetation and associated excavation areas should be kept to a minimum, particularly in areas where soils are unstable. • The construction of roads will create large areas prone to erosion due to soils being exposed. Roads should therefore be constructed in a manner to rapidly stabilise soils, while road side drainage should be included where necessary. For more information, please refer to the SANRAL (2013) 6th Edition Drainage Manual.

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• The construction of the turbines on top of the hills may require blasting of rock associated with both the excavation of turbine foundations and the construction of roads. This activity would need to be managed effectively and include the clean-up of debris. • Construction should be scheduled to take place during the dry seasons when rainfall and associated erosion potential is at its least. • Excavated soils should be stockpiled and separated into separate material types to enable replacement in the same order as excavated, during rehabilitation. • A water tanker should be available to be used for dust suppression should the need arise. • Once the concrete slab is set with the turbine fixed, soil/topsoil should be placed onto the slab with natural vegetation re-established to represent the previous undisturbed environment as closely as possible. • All disturbed areas must be rehabilitated (as soon as possible) to represent the previous undisturbed environment (soil, land-cover, slope) as closely as possible to limit the impact on receiving water resources (by limiting soil erosion). • A practical erosion control handbook should be developed, based on the principles developed in this report and given to the construction contractors to ensure the impact on receiving water resources is limited. • A high voltage powerline is proposed. The location of pylons associated with this powerline have not been assessed as they we’re unavailable at the time of writing. The principles presented in this report (with regards to stormwater and erosion control management) can also be applied to these pylons.

3.2.1 REVIEW OF POTENTIALLY SENSITIVE INFRASTRUCTURE

The thirteen turbine areas and the Substation, Office and Laydown area as identified in Section 3.1 were each considered in more detail. Where necessary, affected infrastructure might require more formal diversions to either divert larger upstream clean catchments or to mitigate possible river flooding through the modification of dirty water diversions. To determine the need for the storm water and erosion control management, each of the thirteen turbine areas and the Substation, Office and Laydown area were further analysed as per Figures 3-2 to Figure 3-5. The analysis considered the following:

• The location of the various buffers (32m river, 100m river, 1km2 contributing area, 0.5km2 contributing area and 0.25km2 contributing area); • 5m contours (from the SUDEM contours provided by the client); • Watersheds (derived from SRTM30 data with rivers ‘burnt’ in); • The location of rivers (from the 1:50,000 topographical map); and • Aerial imagery (South Africa 50cm Colour Imagery captured between 2008 and 2012 by the NGI).

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3 3 7

5 5

5 Legend 3 3 4 7 345 5 0 ± 365 ?! Turbine/Cranepad (100m Intersect) 3 6 5

60 335 3 Substation, Office and Laydown Area 3 4

3 6 0 Turbine Base and Crane Pad

3 50 Overhead Powerline 34 5 0 5 3 Electrical Underground Cables 3 50 Road (New)

Road (Upgrade)

3 2 1 5m Contour (SUDEM) 0 ?! 2 ?! Watershed (SRTM30)

0 Non-Perennial River (50K Topo) 3 3 3 15 Perennial River (50K Topo)

3 3 0 3 2 3 5 3 >1 sq.km Contributing Area

5 >0.5 sq.km Contributing Area 31

>0.25 sq.km Contributing Area 3 1 3 0 25 2 3 0 Flow Path Buffer - Contributing Area

1 8 25m Buffer - (>0.25sq.km) 5

5 1 50m Buffer - (>0.5sq.km) 2 0

1 5

2 0

2 100m Buffer - (>1sq.km)

0 2 32m River Buffer (50K Topo)

100m River Buffer (50K Topo)

5 2

2 0 100 200

1 Meters 9 2 5 Scale: 1:4,000 @ A3 14 5 0 Projection: Transverse Mercator ?! 2 Datum: Hartebeeshoek, LO29 7 5

17 ?! Figure 3-2

0 9 Detailed Assessment of 1

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170 Legend

± ?! Turbine/Cranepad (100m Intersect) 2

0 1 9 175 0 Substation, Office and Laydown Area

18 0 Turbine Base and Crane Pad

Overhead Powerline

185 Electrical Underground Cables 235

Road (New)

20 26 ?! ?! Road (Upgrade) 5m Contour (SUDEM)

Watershed (SRTM30)

Non-Perennial River (50K Topo) 0 3 2 Perennial River (50K Topo)

2 0 2 2 2 >1 sq.km Contributing Area

5 1 2 >0.5 sq.km Contributing Area

0 0 5 1 2 >0.25 sq.km Contributing Area

Flow Path Buffer - Contributing Area 200 25m Buffer - (>0.25sq.km)

14 5 50m Buffer - (>0.5sq.km) 0 2 2 1 3 1 5 4 100m Buffer - (>1sq.km) 0

32m River Buffer (50K Topo)

5 7 1 0 4 100m River Buffer (50K Topo) 2

1 7 0 0 9 1

1 5 5 23 0 0 23 1 5 0 100 200 5 1 Meters 6 0 0 Scale: 1:4,000 @ A3 29 21 33

1 Projection: Transverse Mercator ?! ?! 6 0 5 Datum: Hartebeeshoek, LO29 20

1 8 0 Figure 3-3

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Legend 20 5 ± ?! Turbine/Cranepad (100m Intersect)

Area of Interest 2 2 25 5 2 Electrical Underground Cables

Road (New)

0 0 2 3 2 2

0 Road (Upgrade) 0 2 2 5 0 1 0 2 Crane_Platforms

5 9 1 34 36 Substation, Office and Laydown Area 0

?! 5 ?!

0 2 Turbine Base and Crane Pad

0 5

0 0 2 5m Contour (SUDEM)

Watershed (SRTM30)

Non-Perennial River (50K Topo)

Perennial River (50K Topo)

9 1 >1 sq.km Contributing Area

1 8 0 >0.5 sq.km Contributing Area

5 1 1 9 1 9 8 0 7 1 5 5 0 8 5 1 7 >0.25 sq.km Contributing Area 1

Flow Path Buffer - Contributing Area

25m Buffer - (>0.25sq.km)

5 0 50m Buffer - (>0.5sq.km) 2 160 100m Buffer - (>1sq.km)

1 32m River Buffer (50K Topo)

5 220 5

0 100m River Buffer (50K Topo)

0 100 200 Meters 39 41 Scale: 1:4,000 @ A3 ! ! Projection: Transverse Mercator ? ? Datum: Hartebeeshoek, LO29

1 6 5

Figure 3-4

1 1 5 4 0 Detailed Assessment of 5 Turbines 34, 36, 39, 41

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5 6 Legend 2

1 1 ± 8 7 5 5 ?! Turbine/Cranepad (100m Intersect) 0 5 60 2 2 Substation, Office and Laydown Area 18 !? Turbine Base and Crane Pad

5 16 Overhead Powerline

Electrical Underground Cables

2 7 Road (New) 0 42 1 Road (Upgrade) 7 0

5m Contour (SUDEM)

200 1 1HA FOR TEMPORARY LAYDOWN 8 ! 0 Watershed (SRTM30)

195 Non-Perennial River (50K Topo)

Perennial River (50K Topo)

190 >1 sq.km Contributing Area

>0.5 sq.km Contributing Area 0,5HA FOR OFFICE ! $! >0.25 sq.km Contributing Area

Flow Path Buffer - Contributing Area

$ ! 25m Buffer - (>0.25sq.km) $!

1HA FOR CONSTRUCTION STORAGE 50m Buffer - (>0.5sq.km) !

100m Buffer - (>1sq.km)

32m River Buffer (50K Topo)

100m River Buffer (50K Topo) 270 1.1HA FOR SUBSTATION !

0 100 Meters Scale: 1:3,000 @ A3

Projection: Transverse Mercator Datum: Hartebeeshoek, LO29

Figure 3-5

Detailed Assessment of Turbine 42 & Laydown Area Hydrologic Consulting (Pty) Ltd Consulting Hydrologists 245 I! +27 72 239 0974 I- [email protected] I" www.hydrologic.za.com 2 4 2 0 55 M Bollaert July 2018

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In considering of the various buffers which were used to identify potentially sensitive infrastructure, thirteen turbine areas (01, 02, 14, 17, 20, 26, 29, 33, 34, 36, 39, 41 and 42) as presented in Figure 3-2 to 3-5 were noted as intersecting the 100m river buffer. These 13 turbine areas were identified due to their proximity to a 1:50,000 topographical map river and not a contributing area flow path while none of the 13 turbine areas intersected the more sensitive 32m river buffer. This also revealed that none of 13 turbine areas had an upstream contributing area of more than 0.25km2. The intersection of infrastructure by the 100m river buffer was consequently the result of proximity of the river headwaters to the catchment watersheds with the affected turbine locations positioned on or near these watersheds in most instances. The position of the 13 turbine areas away from riparian areas associated with the 1:50,000 topographical map rivers was also fairly clear given the visibility of indigenous forest ‘corridors’. Accordingly, little to no upstream catchment is present and the development of a management plan which specifically considers the diversion of upstream clean areas is unnecessary. Furthermore, the intersection of the proposed infrastructure by the 100m river buffer does not indicate a potential flood risk, due to the limited contributing areas upstream and the presence of infrastructure on or near the watersheds. The 13 turbine areas were consequently not assessed in any more detail and fall under the generic management plan presented in Section 3.2.3.

Figure 3-5 includes the Substation, Office and Laydown area which while also outside of contributing area flow paths buffers did, however, slightly intersect the more sensitive 32m river buffer by approximately 4m at maximum. This intersection of the 32m river buffer is however, not significant with regards to flood risk since it is above the defined river’s headwater (according to the 1:50,000 topographical map dataset) and is also not visibly within an indigenous forest ‘corridor’ which would clearly indicate the presence of a riparian area.

3.2.2 SITE-SPECIFIC MANAGEMENT PLANS

A site-specific management plan has consequently only been developed for the Substation, Office and Laydown area presented in Figure 3-5 and is specific to just the upslope clean water area. The inclusion of a clean water diversion is necessary to route potential run-on from upstream/upslope through the Substation, Office and Laydown area (necessary due to site topography which does not enable the routing of water around the Substation, Office and Laydown area).

3.2.3 GENERIC MANAGEMENT PLANS

A generic management plan was suitable for all the turbine areas and the Substation, Office and Laydown area (specially the substation, construction storage, office and temporary laydown areas). Under the generic scenario, a dirty area (e.g. wind turbine and crane pad) has a minor upstream clean area of less than 0.25km2 (approximately zero in most instance) and consequently no formal clean water diversion is included. This is due to the marginal clean water area having a potential runoff peak and volume that is small enough to be managed without a formal clean diversion.

Dirty water producing areas are limited to the construction sites during the installation of the various wind turbines, as well as the road, overhead powerline and electrical underground cable network. Once the

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Hydrologic Consulting (Pty) Ltd P a g e | 23 wind turbines are erected and the construction areas rehabilitated, dirty water producing areas will be limited to the road network (depending on the construction and management method) and the construction storage and temporary laydown areas (depending on amount of surface disturbance). It is important to note that equipment such as excavators and cranes will only be used for short periods of time during the construction and erection process of the wind turbines. No heavy machinery and equipment will be used during the operational phase of the project, except potentially for major maintenance activities. Impacts will therefore be limited to sediment control related issues, and not hydro- carbon contamination during the operational phase. Figure 3-6 illustrates a typical wind turbine construction footprint and associated management plan.

FIGURE 3-6: GENERIC EXAMPLE STORMWATER/EROSION CONTROL MANAGEMENT

3.2.4 STORMWATER MANAGEMENT AND EROSION CONTROL

In terms of stormwater management and erosion control, three options have been considered for the site, namely:

1. A berm and channel approach routing to a sediment control area; 2. A silt fence approach; or 3. A combination thereof.

During construction, it will be necessary to determine whether a dirty area can be contained and routed to a single sediment control area, since the location of infrastructure on the catchment watersheds may make this problematic. An additional sediment control area should be included for dirty areas which are divided into two drainage areas due to the presence of a localised watershed.

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BERM AND CHANNEL FOR TURBINE BASE AND CRANE PADS

If using a berm and channel approach, a dirty water area berm/channel as per the generic/conceptual design presented in Figure 3-7, should be constructed around each of the construction sites (all turbine areas and the Substation, Office and Laydown area) using the excavated material for construction of the berm. Figure 3-7 presents design guidelines for the construction of a diversion, with side slopes for all berms and channels at a constant 1 vertical: 3 horizontal, a channel depth (a) of 0.5m and base width (b) of 1.0m.

The berm should be on the outside of the construction area, with the channel component on the inside – thereby enhancing the settling of sediment. The berm and channel combination is aimed to achieve the following:

• Diverting upstream clean water which would otherwise flow into the dirty areas. • Containing dirty water in the dirty areas and allow suspended sediment to settle out. • Providing added flood protection which mitigates residual flood risk (where required).

FIGURE 3-7: TYPICAL BERM AND CHANNEL FOR STORMWATER/EROSION MANAGEMENT SYSTEM

The berm/channel approach (with a channel depth of 0.5m and a base width of 1.0m) was tested using PCSWMM stormwater modelling software as outlined in Appendix A. It was found that for all dirty areas (turbine base and crane pad), the standardised diversion design was sufficient to accommodate runoff from the 1:10 year RI event (assuming a dirty area slope of 5%). The 1:10 year RI event was selected as it represents a reasonable design event for sediment control as outlined by Ferreria and Waywood, (2009). The channel component using the standardised design parameters is more than sufficient, with a peak flow approximating 0.3m3/s for the generic scenario modelled (as illustrated in Figure 3-6). A simplified approach to the construction of the dirty water berm and channel might possibly be achieved using a trench digger or scraper (for instance) which provides sufficient capacity to accommodate flows of at least 0.3m3/s (dependant on site slopes).

For dirty areas, the constructed berm/channel should route runoff to a sediment control area where any entrained sediment can settle as illustrated in Figure 3-6. This sediment control area can be in the form

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Hydrologic Consulting (Pty) Ltd P a g e | 25 of a simplified silt trap or silt fence since runoff rates are low. If a sediment trap is used, recommended containment volumes (based on the 1:10 RI event) would be 610m3 for a turbine area (including crane pad). Regular inspection of the berms/channels and sediment control areas should be undertaken to assess erosion which may result from a loss in vegetation or cavitation from soil slumping.

SILT FENCES FOR TURBINE BASE AND CRANE PADS

Silt fences may be suitable in the control of runoff from dirty areas due to the low peak flows and volumes expected. Accordingly, silt fences could replace the proposed dirty diversions associated with the turbine areas.

The United States Environmental Protection Agency (EPA) provides a detailed guide on the installation and maintenance of silt fences and the reader is referred to the following online document (https://www3.epa.gov/npdes/pubs/siltfences.pdf). As defined by the EPA guide, a silt fence “is a temporary sediment barrier made of porous fabric. It’s held up by wooden or metal posts driven into the ground, so it’s inexpensive and relatively easy to remove. The fabric ponds sediment-laden stormwater runoff, causing sediment to be retained by the settling processes”. A silt fence is possibly a cost-effective approach to stormwater and erosion control management and suits the temporary nature of the construction phase of the project. Dirty water runoff should be distributed (rather than concentrated) if a silt fence is used for sediment control (versus a silt trap) to not to overwhelm the silt fence during significant storm events. The EPA guide can be consulted as to recommended design standards in this regard. Figure 3-8 illustrates a typical silt fence.

FIGURE 3-8: TYPICAL SILT FENCE (AFTER ENVIRONMENT PROTECTION AGENCY2)

2 Illustration of a silt fence installation detail, from U.S. EPA publication, "Developing Your Stormwater Pollution Prevention Plan: A Guide for Construction Sites." Document No. EPA-833-R-060-04.

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SUBSTATION, OFFICE AND LAYDOWN AREA

In considering the Substation, Office and Laydown area, the area requiring sediment control is divided into four blocks totalling 3.6ha. A clean water catchment approximating 4ha is located upslope. Given the topography of the area, it will be necessary to route clean water through the Substation, Office and Laydown area and specifically between the blocks representing the offices and construction storage. The 10 year RI rainfall event over the clean area yields an estimated peak flow of 1.1m3/s with a generic berm and channel design as previously indicated (a=0.5m, b=1m) having sufficient capacity to convey this flow according to the PCSWMM model developed.

The dirty areas represented by the four blocks making up the Substation, Office and Laydown area are to be individually managed. As per the turbines and crane pads, the standardised diversion design (a=0.5m, b=1m) was sufficient to accommodate runoff from the 1:10 year RI event (assuming a dirty area slope of 5% and an impervious area of 50%) with the largest block (the 1.1ha substation) having a peak flow of 0.7m3/s and a total runoff volume of 1,630m3. A berm and channel routing to a sediment control area or a silt fence as previously described should consequently suffice for each of the 4 blocks (assuming they are managed independently to keep peak flows and volumes at a minimum). Continued maintenance of the stormwater and erosion control management system for the Substation, Office and Laydown area may be required through the life of the wind farm dependant on the disturbance to the surface. This may for instance be necessary in the case of the Laydown area and Construction Storage area due to recurrent surface disturbance resulting in deterioration in natural ground cover with and increased potential for erosion.

3.2.5 RIVER CROSSINGS

River crossing designs did not form part of this scope of work and will need to be considered prior to construction. Figure 3-1 presents the river crossings associated with the proposed linear infrastructure intersecting the 1:50,000 topographical map rivers, with 72 crossings identified (not all crossings associated with the proposed overhead powerline are illustrated). Culverts, bridges or low-level crossings will be required to enable the unimpeded use of roads on site. The construction of all roads and crossings on site will need to take cognisance of the 32m and 100m river buffers, wetlands and modelled flood-lines (if they become available). This is so the roads/crossings can be adequately engineered to protect against potential flood risk and to minimise the impact on the water environment.

The design of river crossings requires the selection of a suitable design RI and associated design flow rate. This is a function of the hydrology of the upstream catchment, the type of structure proposed (e.g. low-level crossing or culvert), the cost of construction and the expected maintenance/repair costs in the event of flooding. Applicable design standards for river crossings (inclusive of the required conveyance capacity of culverts and bridges) will need to be agreed with the DWS and should also consider standards as outlined in the South African National Roads Agency Limited (SANRAL) drainage manual (SANRAL, 2013).

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Management measures relating to river crossings to limit their impact of the water environment include the following:

• River crossings should be constructed in a manner so as not to alter the natural hydrological flow regime to such as degree that it would negatively impact river health. • The construction of river crossings will create areas prone to erosion and will destabilise river banks. River crossings should therefore be constructed in a manner to rapidly stabilise soils and river banks. • Site rehabilitation should be undertaken immediately after construction and should restore surface drainage patterns as far as practically and economically feasible.

3.3 OPERATIONAL PHASE- MANAGEMENT PLAN

During the operational phase, it is anticipated that the impact on surface water resources will be limited, particularly if the principles presented in the construction phase (above) are adhered to. The following will however, need to be considered:

• Regular inspection of the wind turbine areas to assess erosion which may result from a loss in vegetation or cavitation from soil slumping; • Continued stormwater and erosion control management for the Laydown area and Construction Storage area assuming these areas continue to be disturbed; • Continued watering to ensure wind erosion is limited at the construction sites until such time that the natural vegetation is effectively established; and • Maintenance and cleaning of all drainage structures along site roads.

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4 CONCLUSIONS AND RECOMMENDATIONS

Baseline information including average rainfall data, depth-duration-frequency design rainfall estimates, evaporation data, soils, vegetation and land-cover information, as well as both regional and local hydrological characteristics have been considered for the proposed Haga Haga Wind Energy Facility in the Eastern Cape. The results of this baseline assessment indicate that the proposed site is in a medium to high rainfall, low to medium evaporation region of South Africa, with moderate to mild slopes.

L Wiles - PrSciNat M Bollaert - PrSciNat, CSci, CEnv

(Project Author) (Project Author)

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5 REFERENCES

Bailey, A.K. and Pitman, W.V., 2015, “Water Resources of South Africa 2012 Study (WR2012)”, WRC Report No. TT??, Water Research Commission, Pretoria

Department of Environmental Affairs, 1998. National Environmental Management Act, 107 of 1998

Department of Water Affairs and Forestry, 1998. National Water Act, Act 36 of 1998

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Department of Water Affairs and Forestry, 2006, “Best Practice Guideline No. G1: Storm Water Management” , DWAF, Pretoria, August 2006

Ferreira, S. & Waygood, C. 2009: “A South African Case Study on Sediment Control Measures with the use of Silt Traps in the Coal Mining Industry. – In: Water Institute of Southern Africa & International Mine Water Association: Proceedings, International Mine Water Conference.” Pretoria

HRU – Hydrologial Research Unit, 1978, “A Depth-Duration-Frequency Diagram for Point Rainfall in southern Africa”, Report 2/78, University of Witwatersrand, Johannesburg, South Africa

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Lynch, S.D., 2004, “Development of a Raster Database of Annual, Monthly and Daily Rainfall for Southern Africa”. WRC Report 1156/1/04. Water Research Commission, Pretoria, South Africa.

Rossman, L., 2008. Storm Water Management Model user’s manual, version 5.0, (March), 271. Retrieved from http://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P10011XQ.txt

SANRAL., 2013 “Drainage Manual - Sixth Edition”, The South African National Roads Agency Limited, Pretoria.

Schulze, R.E. and Lynch, S.E., 2006. “South African Atlas of Climatology and Agrohydrology”, WRC Report 1489/1/06, Water Research Commission, Pretoria

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APPENDIX A – STORMWATER CALCULATIONS

A.1 MODEL CHOICE

PCSWMM is a model package that makes use of the USEPA Stormwater Management Model (SWMM), which is a computer program that computes dynamic rainfall-runoff from developed urban and undeveloped or rural areas (Rossman, 2008).

The SWMM model suits application to this project since it is able to account for:

• Time-varying rainfall; • Rainfall interception in depression storage; • Infiltration of rainfall into unsaturated soil layers; • Evaporation of standing surface water; • Routing of overland flow; and • Capture and retention of rainfall/runoff.

The development of stormwater management plans using SWMM have been undertaken for many thousands of studies throughout the world (Rossman, 2008), including South Africa.

A.2 MODEL SETUP

A.2.1 DESIGN STORM

The SCS Type 2 design storm for South Africa was used to define the rainfall distribution according to the 1:10 year 24-hour rainfall event with a design rainfall depth of 201mm (see Table 2-2).

A.2.2 MODEL PARAMETERISATION

Land cover parameters were estimated according to the surface infrastructure layout with the baseline land cover and soil type being set according Section 2.7. A SCS Curve Number of 56 was used to account for the occurrence of a SCS type A/B soil and veld in fair to good condition. The percentage impervious area was set at 50% (for turbine areas) and 40% (for the Substation, Office and Laydown area) to account for hardstanding as a result of either infrastructure or compaction by site works. Catchment slope for the area of works was set at either 5% or 10% dependant on current slopes (some levelling was assumed). 100% of all runoff was directed to a single channel to simply calculations for the turbine areas. In the case of the Substation, Office and Laydown area, runoff was split into two according to the natural river divide.

A.3 MODEL RUN

Dynamic wave routing was set for the model run along with a time variable step. The resulting runoff continuity error was -0.2% while the routing continuity error was 0%. These errors are near optimum.

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