Integrating Low Impact Development strategies with detention/retention storage for effective stormwater management in an urban watershed.

Urbanization is an inevitable process to attain the development in the modern times. It results in the transformation of the pervious area into an impervious area thus modifying the hydrologic characteristics of a region causing the problem of pluvial flooding. To alleviate the effect of increasing imperviousness in an urban catchment, various techniques to provide detention basins, retention basin and other Low Impact Development (LIDs) are implemented in stormwater drainage network to compensate for the deleterious effect of Urbanization. In the proposed methodology, SWMM provides the simulation of stormwater runoff in one of the basins. Hydrologic modeling of the basin (sub-basin of New Delhi) using SWMM delivers the quantified inundation details in spatial, temporal and volumetric scales. Based on the results from the simulation various Low Impact Development (LIDs) are implemented to study their effects on the hydrological response of the basin. Rain gardens and permeable pavements are adopted for catering the excess flood volume in the subcatchment. The model result confirms the changes in the hydrological response after LID implementation, flood volume reduces up to 23%, and flooding junction has reduced to 33 %. However, LID modifies the catchment characteristics including porosity and infiltration capacity of the soil; it's still far away to achieve the pre-developmental stage. Another mixed scenario was generated where LID and storages were implemented simultaneously in a basin, providing much better results than LID alone. The cumulative effects of retention/detention storages and LIDs help in trapping the desired amount of flood volume, which is prolific in eradicating the pluvial flooding.