Assessing the adequacy of low impact development practices in mitigation of urban flooding

Abstract

Globally flash floods are a major challenge in urban areas causing serious risk to life and infrastructure.They are aggravated by climate change,urbanization and insufficient drainage infrastructure.This is particularly true in Kamwokya II Zone ,Kampala where settlements along the channel experience flash floods during periods of high intensity short duration storms.

The main objective of this study was to assess the adequacy of Low Impact Development(LID) practices in mitigation of urban flooding in Kamwokya II Zone.This involved assessing the adequacy of the existing channel, determining the extent and impact of flooding and formulation of appropriate LID measures. Hydrologic modeling and LID formulation were carried out using EPASWMM Version5.1.The models generated were run for different return periods with the aid of rainfall data obtained from Uganda National Meteorological Authority.

The LID measures incorporated into the catchment were; rainbarrels, raingardens, green roofs,vegetative swales and permeable pavements. Simulation showed substantial reduction in peak runoff hydrographs for the return periods of 5, 10 and 15 years. However, as the return periods increased from 20 to 100 years, the LID effect on peak flows was negligible.

The LID effect was also found dependent on area coverage. Increase in area covered by the LID measure caused an increase in peak flow reduction. LID measures alleviated the pressure on the storm drainage network through peak delay and peak runoff reduction for storms of 5 to 25 return year periods.However, these LIDS are insufficient under higher storm events.