Assessment of the effectiveness of low impact development practices as flood mitigation measure for Namasuba watershed

Abstract

Flooding of urban areas is a worldwide problem as cities grow and the amount of impermeable surfaces increase generating more surface runoff. In Kampala, the capital city of Uganda, flooding occurs in some parts of the city especially in Namasuba suburb along Entebbe road, which has been flooding every rainy season consecutively for a number of years now. The project aimed to mitigate floods, in addition to minimizing the adverse effects of the floods to people and the natural environment. The main objective of the study was to assess the effectiveness of Best management practices as flood mitigation measure. The procedure comprised of field study, data collection, modelling and analysis. The modelling and analysis were done with the help of Storm Water Management Model (SWMM). It was concluded that the major cause of the floods were the soil properties, high percentage of imperviousness, drains blockages resulting from garbage being thrown into the system and silt build-up that accumulates overtime. Additionally, implementing design LIDs scenario 3 which assumes that 50% of the roof runoff enters the Rain Barrels via vegetative swales, 50% of the roof runoff and 50% of the pavement runoff runs into the Rain Gardens, 50% of the pavement runoff flows through the Permeable Pavement, and all eventually enter the urban rainwater system would improve the drainage systems’ rainfall events’ handling capacity to more than 10yrs return period without flooding through reducing and delaying the peak flow downstream. Keywords: LIDs, SWMM, drainage system, floods, and GIS.