Scenario analysis for flood resilient built form-case of Colombo Sri Lanka

Natural flood defence-mechanism is an ecosystem service (ES) that reinforces the community‘s resilience to flooding. The unprecedented urban development with the extensive growth of built-up areas over the last century has absurdly weakened the natural flood defence mechanisms resulting in highly intensive flood exposure and damages. Hence, disaster-resilient city development initiatives should be focused on more sustainable built form scenarios withouttriggering the fragility of Natural flood defence-mechanisms. Low impact development (LID) is technical know-how on a collection of sustainable practices that mimic natural hydrological functions including infiltration, evapo-transpiration or use of surface runoff. In this context, there are certain studies on assessing the compatibility of building regulations with projects underLID, yet there is a gap remains in simulating the effectiveness of LID-based planning and building regulations in building community resilience to flood. Accordingly, this paper attempts to simulate surface runoff level in urban blocks at different LID scenarios in Colombo municipal council area by using the EPA SWMM (the United States Environmental Protection Agency Storm Water Management Model) free and open access flood inundation model. Flood situation at the proposed development scenario in Colombo and hypothetical scenarios were assessed and the results indicate the proposed development scenario leads to the severe urban flooding situation in future. Hence, this study has simulated three hypothetical scenarios, to examine the effectiveness of LID strategies in controlling urban floods while optimising the plot coverage.