Abstract:
Floods are a prominent issue and the challenge of urban flooding can be turned into an opportunity by adopting rainwater harvesting
practices. Rainwater harvesting (RWH) works asa more reliable, cost effective and sustainable way. It is a mean of public contribution to
mitigate urban floods rather than provide a supplementary source of water. The catchment area, maximum rainfall intensity, extent of
building roofs, potential runoff, and outflowof water and estimated capacity of rainwater system are the highlighted six important factors
through the literature. Arc GIS hydrology tools, IDF curves, rational method, the Manning formula and water balance equation were
adopted to calculate the above factors. The relationship between capacity of a rainwater harvesting system (y) and the extent of roof area (x)
has been derived by an equation of y=0.024x. This proposed rainwater harvesting system is potentially applied either in the form of
individual building units or as a common water detention pond. This study has focused on identifying an appropriate mechanism to practice
rainwater harvesting to mitigate urban floods in Colombo.
