Retrofitting L.I.D techniques in urban residential areas: impact on stormwater runoff

Abstract

The demand for housing development in Malaysia for this past decade has seen the conversion of green fields into residential estates. Hence, the design and built of an area are based on the knowledge and techniques available at that time, these housing estates have resulted into the explosion in the amount of impervious surface which disrupt the natural water cycle by converting potential stormwater infiltration into surface runoff. As a result, surface runoff has increased manifold in term of its peak discharge with its concentration time reduced many times its original value. This paper discusses a study carried out to look at the potential of ameliorating this surface runoff issue by retrofitting the existing residential estates with techniques borrowed from Low Impact Development (LID) practices. LID is a development practice advocated to minimize impact on the environment, in the case of stormwater management, finding ways to imitate the natural water cycle as opposed to the conventional end-of-pipe solutions. For this study, the LID techniques adopted include the use of grassed swales and rain garden/bioretention to replace the existing impervious surface where it is appropriate. A section of a residential area about thirty three acres in size was chosen for a series of stormwater simulations using EPA's Stormwater Management Model (SWMM) Version 5.0. A total of two scenarios were simulated by varying the LID treatment accorded to the existing impervious surface in the catchment. The results of the simulations were then evaluated against the existing stormwater runoff characteristics. It is found that retrofitting the existing residential areas with LID techniques could increase infiltration volume, reduce runoff rates by half, lower peak discharges by half and double the time of concentration - depending on the treatment.