Support of the Water Reconciliation Strategy for the Algoa Water Supply System ATSG Meeting

1. Support of the Water Reconciliation Strategy for the Algoa Water Supply System ATSG Meeting Aurecon 07 March 2018

2. Feasibility Component

3. Short-listed Options Upper Coerney Lower Coerney Upper Scheepersvlakte Scheepersvlakte Dam Scheepersvlakte – Nooitgedagt pipeline Nooitgedagt WTW Nooitgedagt North Nooitgedagt South

4. Comparison of Options The risk of failure of these options can be mitigated by providing an additional siphon through the Sundays River, as well as managing the process for quick pipe replacements should it be required. The two Nooitgedagt dam sites should not be evaluated further due to their significantly higher capital cost and other disadvantages.

5. Recommendations • The Nooitgedagt sites should not be investigated further. Although these sites are strategically located near the NWTW, the comparative cost of these options is too high. • The Lower Coerney site is the preferred site, followed by the Upper Scheepersvlakte site. The additional advantage of the Lower Coerney site, besides having the lowest comparative cost, is that water can be supplied by gravity to NWTW. • It is recommended that the topographical survey and geotechnical evaluations commence for the Lower Coerney Dam and Upper Scheepersvlakte Dam sites, to ensure that detailed information for the evaluation of these options is readily available.

6. Next Steps • Geotechnical survey for Lower Coerney and Upper Scheepersvlakte sites: • Geophysical survey – 2 weeks • Rotary core drilling – 3 weeks • Test pitting – 3 days • Laboratory testing – 3 to 4 weeks • Data analysis, interpretation and reporting – 2 weeks. • Topographical survey for Lower Coerney and Upper Scheepersvlakte sites – not started yet • Feasibility design of selected option – to commence once final site has been selected.

7. Additional Slides

8. Lower Coerney Dam The main advantage of this scheme is that it would provide a gravity supply to the WTW via the existing Nooitgedagt pipeline and it can also be filled by gravity flow via a proposed pipeline from the canal.

9. Lower Coerney Dam • Main features of proposed dam: • FSL = RL 99 m to provide a capacity of 4.6 million m3. The lowest drawoff level ~ RL 86 m • About 26,000 m3 of sediment deposited from the catchment and another 4,000 m3 from irrigation inflows over 50 years • Dam catchment area = 34 km2. Safety evaluation flood = about 890 m3/s (attenuation would reduce this to approx 800 m3/s). A concrete-lined side channel spillway with a crest width of 36 m and 5 m of freeboard is required • Proposed dam would comprise a zoned embankment with cobblecrete slope protection • 180,000 m3 storage would be provided for 1 week of storage for irrigation of 750 ha of orchards on Scheepersvlakte Farms • Water quality of low flows in Coerney River may be poor, and measures may need to be provided to reduce the impact on the quality of water in the dam

10. Lower Coerney Dam • Pipeline requirements and operation: • A 1,400 mm diameter 200 m long connector pipe to deliver water from the long weir in the canal to the 1,400 mm pipeline to NWTW and to the proposed 940 m long 1,500 mm pipeline to the Lower Coerney Dam • The 940 m long 1,500 mm gravity pipeline would deliver water to fill the dam and the pipeline would also be used to supply the NWTW in the event of a canal failure • Modifications to the NWTW inlet to make up for head loss and to increase the flow in the existing Nooitgedagt pipeline at times when the storage in the proposed Lower Coerney Dam would be drawn down

11. Lower Coerney Dam Estimated capital costs (excl. VAT) of the proposed scheme:

12. Lower Coerney Dam

13. Upper Scheepersvlakte Dam

14. Upper Scheepersvlakte Dam • Main features of proposed dam: • FSL = RL 128 m to provide a capacity of 4.6 million m3. The lowest drawoff level ~ RL 115 m • Dam storage only utilised in an emergency - only about 4,000 m3 of sediment deposited in the dam over 50 years • Reservoir footprint ~ 60 ha • Dam catchment area = 3.5 km2. Safety evaluation flood = about 220 m3/s – can be accommodated by a relatively small 10 m wide side channel spillway, with 2.1 m of freeboard • The ScD is an embankment dam – therefore likely that suitable earthfill materials are available to construct a zoned earthfill embankment dam with 1:3 u/s slope and 1:2 d/s slope, with cobblecrete u/s slope protection

15. Upper Scheepersvlakte Dam • Pipeline and pumping requirements: • A 1,580 m long 1,300 mm pipeline required to supply the emergency releases of 210 Ml/day (plus 3% losses) from proposed Upper Scheepersvlakte Dam to NWTW • Upper Scheepersvlakte Dam would be filled by pumping as follows: • Water delivered by 1,400 mm pipeline from long weir in the canal to a pump station located below Scheepersvlakte Dam • The pump station would deliver water to Upper Scheepersvlakte Dam via the 1 580 m long 1 300 mm pipeline

16. Upper Scheepersvlakte Dam Estimated capital costs (excl. VAT):

17. Upper Scheepersvlakte Dam