DYASON S KLIP SOLAR ENERGY FACILITY 1 (PTY) LTD. STORMWATER MANAGEMENT PLAN

Transcription

1 DYASON S KLIP SOLAR ENERGY FACILITY 1 (PTY) LTD. STORMWATER MANAGEMENT PLAN Reference: A43448 Prepared for: ATLANTIC RENEWABLE ENERGY PARTNERS (Pty) Ltd Revision: 1 3 November 2014

2 Document control record Document prepared by: Aurecon South Africa (Pty) Ltd Aurecon Centre 1 Century City Drive Waterford Precinct Century City, Cape Town, 7441 T F E W capetown@aurecongroup.com A person using Aurecon documents or data accepts the risk of: a) Using the documents or data in electronic form without requesting and checking them for accuracy against the original hard copy version. b) Using the documents or data for any purpose not agreed to in writing by Aurecon. Document control Report title STORMWATER MANAGEMENT PLAN Document ID A43448/SMP/1 Dyason s Klip Project number A43448 File path Client P:\Projects\_RSK Projects\PRCPTENE03\A43448 Solek Solar Site Transport Studies\03 PRJ Del\6 REP\Dyasonsklip\A43448 DyasonsKlipSolarEnergyFacility1_StormwaterManagementPlan_Oct2014-R1.docx ATLANTIC RENEWABLE ENERGY PARTNERS (Pty) Ltd Client contact Thys van der Hout Rev Date Revision details/status Prepared by Author Verifier Approver 0 30 October 2014 Draft HS HS JHBC JHBC 1 3 November 2014 Final HS HS JHBC JHBC Current Revision 1 Approval Author signature Name Title Approver signature Name Title 3 November 2014 Revision 1

3 DYASON S KLIP SOLAR ENERGY FACILITY 1 (PTY) LTD. STORMWATER MANAGEMENT PLAN Date 3 November 2014 Reference A43448 Revision 1 Aurecon South Africa (Pty) Ltd Aurecon Centre 1 Century City Drive Waterford Precinct Century City, Cape Town, 7441 T F E W capetown@aurecongroup.com 3 November 2014 Revision 1

4 Contents DYASON S KLIP SOLAR ENERGY FACILITY 1 (PTY) LTD. 3 1 INTRODUCTION 1 2 DEFINITIONS / ASSUMPTIONS 3 3 SITE STORMWATER Climate and Land Use Drainage Characteristics Stormwater Calculation Proposed Measures for Stormwater Management 11 4 CONCLUSION 13 Figures Figure 1: Key Plan 1 Figure 2: Typical Vegetation 4 Figure 3: Average Rainfall 5 Figure 4: Average Temperature 5 Figure 5: Drainage Characteristics 6 Figure 6: PV Area Main Catchment Areas. 7 Figure 7: Flow Distribution Facility 9 Figure 8: Access Road - Drainage 10 Figure 9: Typical Detail Berm 11 Figure 10: Typical Detail Outlet with Erosion Protection 12 Tables Table 1: Catchment Areas 7 Table 2: Runoff Coefficient 8 Table 3: Runoff Calculations 9 3 November 2014 Revision 1 Page 1

5 1 INTRODUCTION Atlantic Renewable Energy Partners (Pty) Ltd has engaged Aurecon to prepare a Stormwater Management Plan for the proposed Dyason s Klip Solar Energy Facility 1 (Pty) Ltd. approximately 22km south-west of Upington on the Rem of Farm 454 Dyason s Klip next to the N14. The site location is indicated on the Key Plan below: NAMIBIA N14 VRYBURG N10 PRIESKA KAKAMAS Dyason s Klip Solar Energy Facility 1 (Pty) Ltd. Rem of Farm 454 KENHARDT Figure 1: Key Plan The solar site will be developed to 75 MW capacity. 3 November 2014 Revision 1 Page 1

6 The scope of the study is to prepare a conceptual Stormwater Management Plan (SMP) to support the Environmental Assessment Process of the proposed Dyason s Klip Solar Energy Facility 1 (Pty) Ltd. The scope of the Stormwater Management Plan (SMP) includes inter alia: Determine catchment area for the project site. Estimate floods expected for the catchment. Confirm existing drainage pattern and streams. Propose drainage elements such as side drains, outlets and other mitigation measures to accommodate the flows. Prepare a conceptual drainage layout plan and strategy for the project site. 3 November 2014 Revision 1 Page 2

7 2 DEFINITIONS / ASSUMPTIONS The following assumptions are made (guided by the client requirements): The flood calculation method used Rational Method. The recurrence period normally applied for this type of development to reduce risk of increased maintenance during the operational phase, is 1:50 years. As a principle to minimise earthworks and to minimise changes to the existing drainage patterns, the drainage layout was based on the existing contours. The adjustments to grade and angle for the PV panels is assumed to be taken up by adjustments in the foundation levels. 3 November 2014 Revision 1 Page 3

8 3 SITE STORMWATER 3.1 Climate and Land Use The proposed site is located in a semi-arid area with typically Karoo type of vegetation. Figure 2: Typical Vegetation The main economic activity in the area is agriculture with cattle, sheep and goat farming as well as table grapes and dates, but game farming is also popular. 3 November 2014 Revision 1 Page 4

9 The area experiences summer rainfall in the form of thunderstorms with a Mean Annual Precipitation of below 183mm per annum. Figure 3: Average Rainfall The monthly distribution of average daily maximum temperatures shows that the average midday temperatures for Upington range from 23 C in June to almost 40 C in January. The region is the coldest during July when the mercury drops close to 0 C during the night. Figure 4: Average Temperature 3 November 2014 Revision 1 Page 5

10 3.2 Drainage Characteristics The proposed site is generally flat with gradients ranging from below 0,5% to 1,0% through the site. The PV area generally drains towards the South-East. Dyason s Klip Solar Energy Facility 1 (Pty) Ltd. Figure 5: Drainage Characteristics 3 November 2014 Revision 1 Page 6

11 3.2.1 Drainage Patterns PV Area A1 A2 A3 Dyason s Klip Solar Energy Facility 1 (Pty) Ltd. Figure 6: PV Area Main Catchment Areas. It should be noted that in absence of detailed topographical information, 1:50000 topographical map data was used to establish the drainage patterns. The catchment areas identified are: Table 1: Catchment Areas Catchment ID Area (km²) A A A Access Road Since the access road is directly off the Provincial road, no provision for drainage is expected except for provision at the intersection. 3 November 2014 Revision 1 Page 7

12 3.2.2 Runoff Characteristics The scares vegetation in combination with flat grades and semi-permeable soils yield low runoff coefficients. 3.3 Stormwater Calculation Method and Assumptions For purposes of the SMP the rational method was used. The runoff parameters were based on the following: Return Period A 1:50 year return period was considered. It should be stated that normally a 1:20 year return period should limit risks but a 1:50 year return period will reduce risk for damage and higher maintenance effort further with up to 25% Runoff Coefficient The runoff coefficient was based on the following: Table 2: Runoff Coefficient Slope % Area Permeability % Applied Vegetation % Applied < 3% 100% Very Dense Woods 3% to 10% Permeable 50% Cultivated land 50% 10% to 30% Semi Permeable 50% Grassland 50% >30% Non-permeable Rock The runoff coefficient calculated and used in the flood estimation was 0, Time of Concentration Time of concentration is calculated by the widely used USBR stream flow formula: = 0, Where = Time of Concentration [hours], = Length of waterway [km], = average slope Point Intensity Point intensity is based on standard time of concentration rain fall depth graphs. 3 November 2014 Revision 1 Page 8

13 3.3.2 Runoff PV Area The runoff distribution for the respective catchment areas will be dictated by the layout of the PV area as well as internal roads and channels. However the PV area (which is normally a combination of blocks of similar size) should preferably be orientated in such a way, to minimise impact on natural drainage patterns. A typical configuration (subject to a final site development plan) is indicated in the following figure: LEGEND Drainage Ditch Existing Watercourse Roads Crossing Figure 7: Flow Distribution Facility There are three dominant watercourses crossing through the site and into the main Helbrandkloof stream butting the site on the southern side. These watercourses should be kept clear to ensure minimum interference with drainage patterns. The 1:50 year runoff per catchment area is indicated in the following table: Table 3: Runoff Calculations Time of Peak Runoff Intensity Area Catchment ID Concentration Flow Coefficient (mm/h) (min) (km²) (m3/s) A A A November 2014 Revision 1 Page 9

14 Access Road The position of the access road was not finalised at compilation of this report. However the recommended access is the existing access from N14/4 at km located on Farm 454 Dyason s Klip only. The route follows the watershed for a significant part of the road with only a few small streams crossing at regular intervals. Crossings should be at approximately 500m intervals. The only major crossing is at the entrance to the proposed solar facility where the Helbrandkloof stream needs to be crossed. The approach to stormwater management for the alternative routes (if selected) will be similar. The catchment area for the access road is indicated in the following figure: Legend National Road Provincial Road New Road On Existing Dyason s Klip Solar Energy Facility 1 (Pty) Ltd. Figure 8: Access Road - Drainage Flow and Outlet Conditions The flow velocity and depth at the various outlets will have to be confirmed during detail design stage. Generally, for slopes of between 0,5% and 1%, the average velocity is in the order of 1,2 m/s to 1,6 m/s with depths of 0,3m to 0,5m deep. The flows would generally not cause any serious erosion but appropriate measures should be implemented at outlets to reduce any risk of damage. 3 November 2014 Revision 1 Page 10

15 3.4 Proposed Measures for Stormwater Management General The existing drainage patterns and characteristics should be preserved as far as possible. To that end it is suggested that existing contours (and vegetation) be retained as far as possible and that internal roads are kept to minimum standards. Drainage structures would generally be small diameter pipes (encased in concrete because of the low fill anticipated) or concrete drifts Side Drains In general open drains will be provided along the proposed internal roads or between PV panels. The open drains would be gravel drains with concrete protection at crossings where required Access Road Road drainage at access position to suit existing drainage in National road reserve would be required. Side drains will be provided along some sections of the access road channelling water to the nearest drainage crossing Berms Berms are proposed to prevent external water from entering the PV area and directing flow to suitable areas of release. Figure 9: Typical Detail Berm Outlets All culverts located on the access road have concrete outlets with erosion protection. Side drain outlets should be terminated with suitable erosion protection to reduce the velocity and flow depth. 3 November 2014 Revision 1 Page 11

16 Figure 10: Typical Detail Outlet with Erosion Protection 3 November 2014 Revision 1 Page 12

17 4 CONCLUSION The proposed Stormwater Management Plan presents a proposed strategy for drainage elements required to accommodate the stormwater through the site, between the PV panels and for the access road to the facility. It follows the existing contours to minimise impacts on the existing drainage patterns. The proposed drainage elements should be included in the detailed design to ensure effective management of the stormwater. 3 November 2014 Revision 1 Page 13

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