Comment on nhess-2022-193

Abstract

Urbanization and climate change have challenged the structural integrity of flood-control dams through increased storage requirements and internal water pressures. Many existing dams are aging and have been classified as deficient or having potential for life-threatening floods in the event of failure, thereby necessitating rapid and innovative mitigation strategies (e.g., optimized timing of releases, emergency warning systems, property buyouts, additional storage, diversion levees, underground tunnels). Such alternatives are often screened primarily through a cost-benefit analysis (CBA), where measures of flood-risk reduction are quantified according to inundation bounds and implementation costs. Secondary impacts associated with dam-induced flooding, such as environmental triggers (e.g., toxic pollutant releases, wastewater dispersion, soil erosion, habitat disruption) or social vulnerabilities (e.g., medical needs, language barriers, reinforced poverty, housing challenges), are often included at the screening stage as a series of narratives and are therefore largely indeterminant when ranking alternative strategies. This tendency to screen mitigation strategies through the lens of flood inundation may prioritize solutions with strong hydrological benefits while minimizing additional impacts associated with widespread flooding. To address this gap, we compare a reservoir mitigation strategy using traditional CBA metrics with composite socio-environmental risks through geospatial multi-criteria decision analysis (MCDA) and scenario-based hydrologic/hydraulic modelling. We demonstrate a case study of alternative mitigation options associated with the Addicks and Barker Reservoirs in Houston, Texas, USA under Hurricane Harvey rainfall conditions and compare performance outcomes between the traditional CBA approach and the spatial MCDA approach. This study illustrates how preferred flood management strategies may shift when hydrologic outputs are integrated explicitly with socio-environmental factors at the preliminary screening stage. By leveraging the strengths of composite risk indicators and simplified spatial overlay methods, the MCDA framework aids decision-makers in visualizing multi-functional benefits from disparate mitigation options and provides an additional layer of information for optimizing the system.