Abstract
Simulation of flood inundation in urban areas longer important, given the magnitude of potential loss and disruption associated with non-river based, urban flooding. The complexity of the urban environment and lack of high-resolution topographic and hydrologic data compromise the development and implementation of models. Low impact development (LID) is technical know-how on a collection of sustainable practices that mimic natural hydrological functions including infiltration, evapotranspiration or use of surface runoff. Several studies have been carried out to discuss the impact of urbanization scenarios in reducing the urban flood risk in watershed scale in Sri Lanka. Yet, there is a gap remains in simulating the effectiveness of LID-based planning practices to reduce flood risk with the complex built form scenarios. In such a situation, this study attempts to make a significant contribution to simulate the variations of flood regulation functions under different high-intensive urban development scenarios, particularly focusing on the urban metropolitan regions. The analyses were carried out utilizing SWMM (Storm Water Management Model) which is open-source flood inundation simulation approach with the help of GIS in a more qualitative manner. The simulation results indicate that expanding built form scenarios increase the flood venerability for city functions, increasing inundation duration and LID scenarios able to reduce the surface runoff to reduce flood vulnerability at a significant level. The simulation results had been verified with the real ground situation (mean percentage change < 15.5%) which able to capture the thresholds of built form variation, as well as dynamic land uses and infrastructure supply which can be used as a tool for future planning practices and decision-making.
Highlights
Expanding urban areas predispose a huge challenge for making cities resilient to extreme weather events
MODELLING SURFACE RUNOFF In this study model the surface run off using the EPA SWMM (United States Environmental Protection Agency Storm Water Management Model) is a free and open access flood inundation model which can be used under deterministic modeling scenarios to simulate water inflows, outflows, and storages within a sub-catchment
Urban built-up area expansion increases the risk of urban flooding and waterlogging
Summary
Expanding urban areas predispose a huge challenge for making cities resilient to extreme weather events. Climate change has multiplied hydro-meteorological hazard events into 3,253 over the past decade (2005-2015), which was five times greater than the 743 catastrophes reported in the 1970s (WMO, 2015) (WMO, 2014) (UNDRR, 2015). I.e., changing rainfall patterns, increased rainfall intensity, high frequency of storms; may lead to serious urban storm water issues, including property damage, loss of lives, economic and neighbourhood impacts and perturbations to the ecosystem services as well (Chen, et al, 2017). Flash floods due to increasing urbanization pose huge challenges in urban planning for a sustainable future (Jayasinghe & Munasinghe , 2013), (Abenayake, et al, 2016). Limited-availability and validity of accurate methods to predict future and existing flood situation with urban expansion scenarios become a critical challenge for decisionmakers and urban planners (Abenayake, et al, 2020)
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