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.

Keywords

Flood damage / Flood mitigation measures / Inundation area / Inundation depth / Vulnerability curves

Relevance to resilience

The study makes a significant contribution to increasing urban resilience by addressing prevailing vulnerabilities within urban environments due to flooding. The methodology of the study was systematically formulated to generate data-driven, results-oriented decisions using the application of GIS-based hazard mapping, hydraulic modelling for inundation mapping and vulnerability curves in economic assessments. The hazard assessment was formulated to discover different hazard levels within the study areas of Colombo, Sri Lanka and Auckland, New Zealand, while the study can be applied to urban environments elsewhere facing similar urban floods. Simultaneous studies of flood inundation mapping and economic assessments provide a methodology flow chain to evaluate the effectiveness of structural flood mitigation measures in terms of flood inundation depth reduction and flood damage reduction. Under flood damage estimations, both tangible and intangible asset damages were comprehensively assessed to provide a holistic view of flood impacts. Even though the preliminary assessments were carried out for the selected pilot areas, they are scalable and adaptable for worldwide scenarios and directly support urban resilience improvements, enabling proactive planning and optimisation of flood mitigation measures, identifying unique characteristics in different research areas. This will reduce economic and societal costs due to flooding and enable a rapid recovery, establishing city resilience.

CRediT authorship contribution statement

Paboda Jayawardane: Writing - review & editing, Writing - original draft, Visualization, Validation, Software, Methodology, Formal analysis. Lalith Rajapakse: Writing - review & editing, Supervision, Resources, Project administration, Conceptualization. Chandana Siriwardana: Writing - review & editing, Supervision, Project administration, Conceptualization.

Conflict of interest statement

The authors declare no conflicts of interest related to this study.

Acknowledgement

The Sri Lanka Land Development Corporation (SLLDC) is gratefully acknowledged for its valuable support in providing data and insights related to structural flood mitigation measures, which were instrumental in conducting the study.

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