Investigation of multiple flood mitigation strategies for an urban catchment using semi-distributed hydrological modelling

Flood mitigation is necessary to protect urban population especially in Asian countries. Particularly in India, evidence-based research for the implementation of flood mitigation measures is quintessential. This paper investigates flood mitigation measures for Chennai, an urban area in southern India using the Hydrologic Engineering Centre-Hydrological Modelling System (HEC-HMS) model. Interactive supervised classification of Landsat imagery for land use/land cover (LULC) mapping and Thiessen polygon-based rainfall are used in the HEC-HMS model. The results show that increasing the capacity of tanks by 20% and incorporation of Soil Conservation (SC) measures leads to 3.34% and 4.91% reduction in peak discharge, respectively. Hence, evidence is less to suggest that increasing the capacity of tanks by 20% will have significant effect to mitigate the 2015 flood. Construction of Orathur reservoir, with an initial volume of 18.42 Mm3 before the flood event, leads to a reduction in peak by 7.52%. The creation of flood channel alone attenuates 14.79%, and combination of construction of reservoir along with SC measures in the upstream watersheds leads to an attenuation of 12.12%. Although the natural flood management practices may not lead to significant attenuation in the case of extreme events, the combination of SC measures and construction of Orathur reservoir and flood channel produce a maximum decrease in peak by 26.86%. This investigation of multiple flood mitigation measures reveals that the mitigation of extreme events like 2015 would be hydrologically possible, although limited in capability, and it would be better helped if proper floodplain management policies are in place in urban areas. © 2021, Saudi Society for Geosciences.