Integrated flood risk management for urban resilience: A multi-method framework combining hazard mapping, hydrodynamic modelling, and economic impact assessment

Abstract

Flooding has become an emerging global catastrophe, generating considerable damage to both infrastructures and lives. Despite the critical need for quantitative assessments of both flood damage and the effectiveness of flood mitigation measures, most existing studies have focused on isolated aspects of flood risk. Only a very limited number of studies have comprehensively integrated hazard mapping, hydrodynamic simulations, and economic damage estimations to evaluate the real-world impact and effectiveness of flood mitigation measures (FMMs). This study presents a multi-method approach to evaluate the performance of such established structural FMMs. Initially, hazard assessments for two selected case study areas, the Colombo Metropolitan Area in Sri Lanka and Auckland, New Zealand, two flood-prone cities with contrasting geographical contexts. Flood inundation mapping for the Madiwela South Diversion, Colombo, Sri Lanka, was performed using hydrodynamic modeling to demonstrate the reduction in flood inundation area and depth after the implementation of the measure, considering six (6) design return periods (RPs). Subsequently, tangible and intangible property damage estimations for “without FMMs” and “with FMMs” were evaluated to identify the benefit of responding to flood conditions, utilising a vulnerability-based economic analysis. In addition to damage estimations, the study adopts a novel approach by conducting an investment viability analysis to find the Benefit-to-Cost ratios and Net Present Value of nine (9) selected FMMs implemented by Sri Lanka Land Development Co-operation (SLLDC). The FMMs implemented by SLLDC were selected from Colombo, Sri Lanka. The quantified damage estimates revealed a reduction in flood damages ranging from 39 % to 63 %, alongside a decrease in flood inundation depths between 9 % and 12 %, and the results underscore the significant effectiveness of FMMs in managing urban flooding and minimising its impacts. This cross-disciplinary methodology enables a transferable framework for resilience-oriented urban planning in diverse hydrological and geographical contexts.