MANAGED AQUIFER RECHARGE (MAR) FOR STORMWATER MANAGEMENT ON THE CAPE FLATS, CAPE TOWN Benjamin Mauck Supervisor: Kevin Winter 11 th November 2015 www.wsud.co.za
2 I NTRODUCTION South Africa’s urban areas are becoming increasingly vulnerable to water scarcity. • Mediterranean climate • Highly urbanised • Ecologically sensitive • Prone to water scarcity • Stressed surface water resources • Economic Growth • Population Growth • Climate change
3 W ATER S ENSITIVE U RBAN D ESIGN • Sustainable stormwater management (SUDS) • Reuse of water (i.e. MAR), • Alternative supply sources (i.e. Groundwater), • Improving aesthetic and recreational appeal of urban water.
4 WSUD – M ANAGED A QUIFER R ECHARGE Stormwater Management Water Supply
5 S TUDY S ITE - C APE F LATS Durbanville Tygerberg Cape Town Kuilsriver Muizenberg
6 C APE F LATS - G ROUNDWATER
7 R ESEARCH O UTLINE • The main objective is to test the applicability of Managed Aquifer Recharge (MAR) on the Cape Flats: • Integrated modelling approach MIKE SHE/MIKE 11. • Is it possible to infiltrate winter stormwater into the CFA for the purpose of stormwater Managment? • Can this infiltration be optimised by increasing abstractions from the CFA for fit-for-purpose uses during the summer months?
MIKE SHE – I NTEGRATED H YDROLOGICAL 8 MODELLING Overland flow Precipitation and flooding River flow Evapotranspiration (MIKE 11) Unsaturated Urban Zone Flow infrustructure (MIKE URBAN) Saturated Groundwater Flow Water Quality
MIKE SHE – I NPUTS 9 Rainfall Land Use Potential Evaporation Soil Types (UZ) MIKE 11 Geology (SZ)
MIKE SHE – GW L EVELS 10 Mean Head Elevation Groundwater Levels R 2 = 0.45 R 2 = 0.63 R 2 = 0.76 R 2 = 0.80
MIKE SHE – H EAD E LEVATION 11 Observed Mean Error = -1.6m Simulated Mean Error = -0.4m
MIKE SHE – R ECHARGE 12
MIKE SHE – F LOW 13
14 MIKE SHE – S TORMWATER M ANAGEMENT ? How much stormwater can be stored? How much abstraction is needed? How long would it take to refill the • High Water aquifer? Table What are the possible uses for • Urban abstracted water? Flooding • Lower Water Table • Lower Flood Risk • High summer Demand
N EXT S TEPS … 15 Calibrate MIKE SHE at a regional scale : • 1980 – 1984 • 2010 – 2015 • Compare Model performance • Select optimal sites for MAR: • Model output • Flood mapping • Land use • Water Quality • Scenario simulation using local scale MIKE SHE models. • Artificial Recharge • Abstraction (Pump tests) • Climate Change
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17 C APE F LATS A QUIFER • Number of studies since the 1970’s : Henzen,1973; Wessels and Greeff, 1980; Hay,1981; Tredoux,1983 &1984; Vandoolaeghe, 1989 &1990; Fraser and Weaver, 2000; DWAF 2007 & 2008. CSIR: DWAF: Berg CMA • Potable water Report. The CFA Reviewed for supply was an area of bulk water • Waste water interest. supply treatment • potential. Re-use 1970 2000 2015/2016 2007-2008 Early 1980’s Late 1980’s Reviewed Increasing CFA again for bulk Exploration CFA Interest: water supply Hydrogeological • UCT, Delta H, potential. Properties. Umvoto, CSIR, CoCT & DWS
18 M ODEL S ELECTION • Stormwater models (SWMM, MOUSE, P8 or MUSIC ) lack detailed groundwater representation. • Coupling urban stormwater and groundwater models (i.e. SWMM and MODFLOW): • Lack of communication/feedback at each time step. • DSS - Established urban groundwater Decision Support Systems: • Data intensive • Complex model structure • Integrated hydrological models – MODHMS, HGS, MIKE SHE : • Fully integrated surface- and ground-water capabilities, • Spatially distributed, • Simpler model structure, • Flexible model requirements (data availability or conceptual model), • MIKE SHE can link urban stormwater model MIKE URBAN.
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