Retrofitting Stormwater Ponds to Infiltration Ponds

Abstract

Cape Town is a city with over four million people and a growing population. Due to three consecutive dry summers as a result of climate change, a growing population and an increased per capita water demand, the city’s main water supply was nearly depleted. Cape Town depends for 98% on surface water stored in dammed reservoirs, which is replenished by rainfall. There is a temporal mismatch between water availability and peak demand, and thus harvesting rainfall can be potentially become an additional source of water. Cape Town’s urban drainage system has 737 detention ponds, which are used to attenuate flooding in case of heavy rain events. These ponds can be used to harvest the stormwater and store it in the Cape Flats aquifer using managed aquifer recharge for seasonal availability. The complexity of retrofitting stormwater ponds into infiltration ponds calls for a systematic approach. This research offers a retrofitting framework for the context of Cape Town. The framework can be used to determine suitable detention ponds to allow managed aquifer recharge via infiltrating stormwater, and to retrofit these detention ponds into infiltration ponds. The framework consists of three phases; spatial assessment, physical assessment and conceptual design. It is highly flexible in usage due to the fact that every phase can be used separately. Additionally, the framework can be extended to include important socio-economic aspects. Following the framework standardizes the procedure of obtaining data on individual ponds, which allows for objective comparison in assessing their suitability for infiltration.