GROUNDWATER A SOURCE OF WATER FOR THE DEEP SOUTH

Roger Parsons 1, John Coetzee 2 and Chris Wise 2

1Parsons and Associates Specialist Groundwater Consultants, PO Box 2606 7129. Tel (021) 855-2480. E-mail: [email protected] 2Jeffares and Green (Pty) Ltd

ABSTRACT

Adequate supply of water to the southern suburbs of , including , Simon’s Town and Noordhoek, is increasingly coming under threat as these suburbs expand and their demand for water increases. Upgrading and expanding existing water reticulation pipelines through to these areas is possible, but will be expensive and disruptive. Alternative sources of water were hence considered, including the construction of a dam at Brooklands above Simon’s Town and development of local groundwater resources. This paper describes the potential for developing groundwater resources to increase a secure supply of water to these areas.

INTRODUCTION

The area south of Clovelly – including Fish Hoek, Noordhoek, Simon’s Town, Scarborough and – currently obtains water from water resources above Simon’s Town (Lewis-Gay Dam, Kleinplaas Dam, and Rawson Dam) and via a pipeline running through Muizenberg and . A dam site at Brooklands was identified some 30 years ago as a potential future source of water to augment existing supplies (Figure 1). In response to a land claim – parts of which would be flooded should the dam be built - the investigated whether the Brooklands Dam site was still required. To be able to make an informed decision regarding the reservation of the land for construction of the Brooklands Dam at some point in the future, the City of Cape Town commissioned a study to investigate water resource and supply options for the area colloquially referred to as the Deep South. The study included an economic evaluation of various water resource and supply options, assessed the security of supply for the Deep South area and attempted to ascertain related environmental and social issues. This paper describes prevailing groundwater conditions and the feasibility of developing groundwater as a source of water for the area.

WATER DEMAND AND SUPPLY

Based on 1996 census data, the population of the Deep South is in the order of 50 000 (Figure 1). In addition to the established residential component and the naval base in Simon’s Town, a large portion of the study area comprises the National Park. The Average Annual Demand (AADD) for the Deep South area in 2001 was estimated at almost 17.0 ML/d (Jeffares & Green, 2003)(1). This includes un-metered usage (7%) and background losses (8%).

It was projected the population of the area would increase from 50 000 in 1996 to almost 100 000 by 2030. After taking account of increased service delivery and effects of water demand management, Jeffares & Green (2003)(1) predicted the AADD in 2027 would be in the order of 33 ML/d, with a peak daily demand factor of 2.2. The maximum yield of the existing water supply system was estimated to be about 30 ML/d and should be sufficient to meet project water demand until 2027. However, concerns about the age and fragility of the pipeline (risk of failure) and security of supply (reliance on a single pipeline) necessitate establishment of additional sources of water.

Proceedings of the 2004 Water Institute of Southern Africa (WISA) Biennial Conference 2 –6 May 2004 ISBN: 1-920-01728-3 Cape Town, Produced by: Document Transformation Technologies Organised by Event Dynamics Settlements

Noordhoek

Kommertjie Fish Hoek

Glencairn

Ocean View Simon’s Town City of Cape Town

Scarborough

Deep South

Dams f Groundwater

Unit 4 Units

f

Lewis Gay Unit 3 f Kleinkrans proposed Brooklands Fish Hoek Primary Aquifer Noordhoek Jackson Primary Aquifer f Rawson Unit 2 f

f Unit 1

Figure 1. Locality map showing major settlements, dams and the extent of groundwater units in the Deep South.

The Deep South currently receives its water supply from a pipeline passing through Muizenberg and Clovelly to Simon’s Town and from smaller dams above Simon’s Town (i.e. the Lewis Gay Dam, Kleinplaas Dam, Rawson Dam and Jackson Dam). Water received from the Muizenberg-Clovelly pipeline is predominantly fed from Theewaterskloof Dam via the Blackheath or Faure Water Treatment Plants. Raw bulk water from the Lewis Gay Dam and Kleinplaas Dam is treated by the City of Cape Town at the Brooklands Water Treatment Plant. Currently, the pipeline yields about 13 ML/d and the Lewis Gay and Kleinplaas Dams collectively yield 3.3 ML/d. Raw bulk water from the Rawson Dam and Jackson Dam, owned by the South African Navy, either serve as strategic storage or is treated by the navy for their own consumption.

WATER RESOURCE OPTIONS

Prior to establishment of the Unicity in 2001, the responsibility of water supply was a function of individual local municipalities. The Brooklands Dam site was identified as a potential source of water by the Simon’s Town Municipality in 1968 (Ninham Shand, 1969) (2). The municipality intended to construct the dam once the purchase of water from the then Cape Town City Council exceeded the cost of developing the dam.

Following restructuring of local government in 1997, the Cape Metropolitan Council took over responsibility for bulk water supply to the area. Based on an investigation into the immediate need for the proposed Brooklands Dam, it was decided the Muizenberg-Clovelly pipeline would be used to meet growing water demand. A series of booster pumps were then installed to increase the flexibility of the reticulation system.

A series of land claims and subsequent adjudication by the Lands Claims Commission prompted further investigation into the need for the Brooklands Dam. If the land claims are successful, and if the Brooklands Dam is not required, the possibility exists of returning this land to the claimants. Water demand in the area had to be assessed as well as potential sources of future water supplies.

Additional water supply options considered included: • construction of the proposed Brooklands Dam • construction of a new supplementary water supply pipeline from Muizenberg • development of groundwater supplies • desalination • various combinations of the above

GROUNDWATER CHARACTERISTICS

Geology The Deep South is underlain by granitic rocks of the Cape Granite Suite and sedimentary rocks of the Group (TMG). Fractured and faulted rocks of the TMG form significant secondary aquifers in the Western and Eastern Cape (Pietersen and Parsons, 2001)(3), capable of yielding large quantities of good quality groundwater on a sustainable basis. The contact between the TMG and underlying granites is also considered to be an important target for drilling. Two significant occurrences of Tertiary to Recent unconsolidated sand deposits also occur in the area, which form locally significant primary aquifers.

Depth to groundwater is generally a function of elevation above sea level. In lower lying areas, the groundwater piezometric surface is relatively close to surface, but in higher lying areas, groundwater levels may be in the order of 20 to 50 m below surface. Very little groundwater level data were available during the study and it was hence not possible to assess groundwater flow directions nor the compartmentalisation of aquifer units in the area of interest.

Numerous faults occur in the study area, which generally lie in a northwest – southeast direction (Figure 1). Presence of these faults suggests a good potential for drilling high yielding boreholes as faults and fractures enhance the ability of geological formations to transmit groundwater. On the basis of the position of the faults, those parts of the study area underlain by hard rock aquifers were divided into 4 separate geohydrological units (Figure 4).

Similarly, unconsolidated deposits form two locally significant primary aquifers in the Deep South, one in the and the other in Noordhoek (Figure 1). Aquifer Yield To be able to provide a preliminary assessment of the potential of groundwater for further development, it was assumed estimation of recharge would provide a measure of the sustainable yield of the groundwater system. Mean Annual Precipitation (MAP) in the area varies between 630mm/a in Fish Hoek and 1300mm/a on top of the mountains. Recharge of the TMG Aquifers is difficult to quantify without adequate data, but 15% MAP is generally accepted as a reasonable conservative estimate in high rainfall areas (Parsons, 2001)(4). Based on work in Atlantis (Fleisher, 1993)(5) and in the (Vandoolaeghe, 1990)(6), recharge for the primary aquifers was assumed to be 30% of MAP. In calculating recharge, all areas within 1 km of the coast were excluded. Because of the threat of saline intrusion, production boreholes would not be placed in this zone. The potential yield of the six delineated geohydrological units is presented in Table 1.

Table 1. Potential yield of groundwater units in the Deep South. Groundwater Units Recharge (ML/d) Unit 1 11.0 Unit 2 12.6 Unit 3 8.3 Unit 4 8.0 Fish Hoek primary 8.5 aquifer Noordhoek primary 2.2 aquifer Total 50.6

It is unlikely this potential yield will ever be fully realised. For environmental reasons, large-scale groundwater abstraction from the primary aquifers is unlikely to be approved. Haupt (2002, pers.comm.)(7) estimated the exploitation potential of the TMG Aquifer would be in the order of 50% (8) of the harvest potential calculated by Baron et al. (1998) .

Based on past performance, the long-term yield of individual boreholes drilled into TMG Aquifers range between 5 and 10 L/s per borehole. It is thus estimated a well-sited and managed borehole is capable of yielding between 0.5 and 1.0 ML/d. Between 6 and 10 production boreholes would be required to augment the water supply of the Deep South by 5 Ml/d, and thereby match the total assured yield of the proposed Brooklands Dam estimated by Jeffares & Green (2003)(1)1. Exploratory work by Rasmussen et al. (1995)(9) in the Simon’s Town area and drilling into the TMG Aquifer in the vicinity of the Clovelly Golf Course by Maclear (2000)(10) confirmed that these volumes can be obtained from properly sited boreholes in the TMG Aquifer, but probably not from boreholes drilled into the underlying granites.

Location of Production Boreholes High yielding boreholes in TMG Aquifers are generally associated with structural features such as fractures and faults. Fractures and faults should hence be targeted as locations for boreholes, particularly in those areas where faults intersect each other. If the threat of seawater intrusion is to be avoided or reduced, it is advisable not to drill within 1 km of the coastline. While it is accepted that careful placement of boreholes could significantly reduce infrastructure costs, past experience in the Simon’s Town area has shown geohydrological considerations are paramount with respect to drilling successful boreholes. Final selection of drilling targets hence must be based on geohydrological conditions and vehicle access.

Boreholes should be drilled to at least the contact between the TMG and underlying granite, which is approximately at sea level. The required depth of boreholes will thus be determined by the elevation of the ground above sea level.

In order to make the best use of the existing water bulk distribution network it is proposed that the

1 Latest estimates suggest the yield of the proposed Brooklands Dam would be about 2.5 ML/d. majority of boreholes be drilled on the higher lying area above Simon’s Town and Ocean View. In this way the borehole water could be transported via gravity pipes to the Brooklands Water Treatment Plant and onto the Prince George and Neptune reservoirs. However, it may also be beneficial to place boreholes above certain of the more remote areas such as Scarborough or San Michel, thereby reducing reliance on the pipeline infrastructure to these settlements.

Water Treatment The groundwater is expected to generally have a NaCl character, a low TDS (electrical conductivity less than 50 mS/m) and pH between 5.5 and 7.0. However, the groundwater may yield elevated Fe and Mn concentrations, which may require treatment such as aeration. Groundwater from the Peninsula Formation is often soft, aggressive and corrosive (Mackintosh & de Villiers, 2001)(11).

If the groundwater is of a very different type to the raw surface water, it may not be advisable to blend the waters at the Brooklands Water Treatment Plant before treatment. A separate treatment unit may thus be required at the Brooklands site. Also, any isolated boreholes may require their own package treatment plant. The need for treatment needs to be considered in light of the quality of groundwater encountered during exploration drilling and testing.

Economic Evaluation Jeffares & Green (2003)(1) undertook an economic evaluation of the various water supply alternatives considered. By comparing the Unit Reference Value of each water source supplying 5 ML/d, it emerged groundwater was the least expensive source of water (Table 2). As the operating costs alone of desalination range between R 5.50 and R 11.00 /KL, desalination is discounted as an economically feasible option.

Table 2. Comparison of the Unit Reference Value of different supply options. Unit Water source Reference Value (R/Kl) Existing water via Muizenberg-Clovelly pipeline and pumping 1.50 stations Skuifraam water via Muizenberg-Clovelly pipeline and 2.00 pumping stations Brooklands Dam and Water Treatment Plant 1.59 Groundwater development 1.38

It is noted the economic analysis did not take into account environmental costs, nor did it consider the economic benefits of phasing in groundwater schemes over a period of time and thereby delaying capital expenditure until actually needed.

Current Groundwater Use The extent of groundwater use in the Deep South is not yet appreciated, but is to be assessed shortly by a hydrocensus of the area. Summer abstraction of groundwater for garden irrigation in Fish Hoek could amount to some 0.8 ML/d (Parsons, 2000)(12). Water for irrigating the Clovelly Golf Course is also sourced from boreholes and probably amounts to 1.2 ML/d. While not included in the reticulated water supply system, this use of groundwater significantly reduces summer demand from reticulated supplies.

DISCUSSION

Groundwater is widely used throughout the world as a source of urban water supply. Out of necessity, it is used to supply more than 300 towns in South Africa with water – either as a sole source or in conjunction with surface supplies. Because of its intangible character, groundwater is generally poorly understood and often not trusted as a reliable and sustainable source of water by water resource planners and managers. This is particularly true in areas adequately supplied by surface water supplies. However, the development of groundwater has a number of advantages, including: • lower cost • the ability to be developed in a phased manner (and thus delaying capital expenditure) • less prone to the effects of drought

Proper exploration and testing based on good science is required to reduce or remove uncertainties regarding the resource and its ability to be developed as a sustainable and reliable source of water.

In addition to the reuse of wastewater (particularly for the irrigation of sports fields and parks and for industrial use) and the implementation of water conservation and demand management practices, construction of the proposed Brooklands Dam and development of groundwater supplies appear the most feasible options. This is particularly true when considering economic and security of supply factors.

Implementation of an exploration project and - if warranted – a pilot groundwater abstraction is required to test, demonstrate and verify the feasibility of developing groundwater supplies for the Deep South. The exploration programme should include a hydrocensus of existing boreholes in the area, drilling and testing of between 6 and 8 exploration boreholes and implementation of a groundwater monitoring programme. Should the collected information continue to support the contention that groundwater could be used as a source of water, a pilot abstraction scheme is recommended. This pilot scheme would be used to monitor the response of the groundwater system to pumping, better quantify the yield of the aquifer and determine potential impacts of abstraction. Because of the need to timeously collect the required data, it is recommended that the exploration and testing phase be implemented well before the Deep South starts to experience shortages and disruptions to water supply.

CONCLUSIONS

Based on an understanding of the prevailing geology and a desktop assessment of geohydrological conditions, it appears groundwater could play a significant role in meeting the future water demand of the Deep South and / or delaying significant capital expenditure. Between 6 and 10 boreholes will be required to produce 5 ML/d. To be better able to assess the yield of the aquifer and groundwater quality, a programme of further exploration is required. If this exploration confirms the findings of the desktop assessment, then a pilot abstraction scheme should be implemented.

ACKNOWLEDGEMENTS

The City of Cape Town is thanked for granting us permission to use information gathered during the Deep South project to prepare this paper. Views expressed in this paper are those of the authors and do not necessarily reflect those of the City of Cape Town. Much of the paper was based on information presented in the Jeffares & Green (2003)(1) report and this source is fully acknowledged.

REFERENCES

1. Jeffares and Green, Water Resource and Supply Options Study: Area South of Clovelly (Deep South); Report prepared by Jeffares & Green for the City of Cape Town (2003). 2. Ninham Shand, Augmentation of the Water Supply and the Reticulation for the Municipality of Simon’s Town – Revised Report, Report prepared by Ninham Shand (1969). 3. K.P. Pietersen & R.P. Parsons, A synthesis of the hydrogeology of the Table Mountain Group – formation of a research strategy; TT 158/01, Water Research Commission, Pretoria (2001). 4. R.P. Parsons, Recharge of Table Mountain Group aquifer systems (2001); in K.P. Pietersen, and R.P. Parsons, A synthesis of the hydrogeology of the Table Mountain Group – formation of a research strategy; TT 158/01, Water Research Commission, Pretoria (2001). 5. J.N.E. Fleisher, Calculation of natural groundwater recharge from sand dune areas with the Cl method; GWD Conf. Proc. Africa needs ground water, University of the Witwatersrand, September 1993, Paper 23 pp 1 – 11 (1993). 6. M.A.C. Vandoolaeghe, The Cape Flats aquifer; Technical report GH3687, Directorate of Geohydrology, Department of Water Affairs and Forestry (1990). 7. Haupt (pers.comm.) (2002). 8. J. Baron, P. Seward & A. Seymour, The groundwater harvest potential map of the Republic of South Africa; Technical report Gh 3917, Directorate of Geohydrology, Department of Water Affairs and Forestry (1998). 9. J.M. Rasmussen, J.A. King & A.J. Lombaard, A hydrogeological assessment of selected localities in the Simon’s Town Municipal area, ; Report prepared by PD Toens & Associates for the Simon’s Town Transitional Metropolitan Structure (1995). 10. L.G.A. Maclear, Clovelly Country Club – Augmentation borehole for irrigation water supply; Report 273297 prepared by SRK Consulting for the Clovelly Country Club (2000). 11. G.S. Mackintosh & H.A. de Villiers, Treatment of soft, acidic and ferruginous groundwaters (2001); in K.P. Pietersen & R.P. Parsons, A synthesis of the hydrogeology of the Table Mountain Group – formation of a research strategy; TT 158/01, Water Research Commission, Pretoria (2001). 12. R.P. Parsons, Silvermine River Catchment ICMP – Geohydrological assessment; Report 055/SILV-F1 prepared by Parsons and Associates for the South Peninsula Municipality (2000).