Assessing the effectiveness of blue-green infrastructure for flood mitigation and alternative water supply provision: a watershed-scale study in Bahir Dar City, Ethiopia Open Access

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This study assesses the effectiveness of two blue-green infrastructure (BGI) measures – wetlands for flood mitigation and rain barrels for alternative water supply. We employed the three points approach (3PA) framework, which categorizes hydrological events into day-to-day, design, and extreme domains based on characteristic return periods. Then, we developed twelve model scenarios, combining the three domains with four BGI implementation strategies, including a do-nothing baseline. BGI effectiveness was assessed by comparing nine implementation scenarios against three baseline scenarios using various performance indicators and efficiency metrics. Results demonstrate notable reductions in peak flow, with some scenarios achieving up to 74.62% locally and 41.32% at the catchment outlet. Maximum flood volume reduction efficiency was 73.33, 48.04, and 44.62% in the day-to-day, design, and extreme domains of the 3PA, respectively. Monthly water-saving efficiency ranged from 7 to 27%. Unlike prior studies focusing on site-scale analysis, this research provides a watershed-scale evaluation of BGI efficiency. Additionally, it introduces a physical-model evaluation aspect into the 3PA. The study also aims to inspire further research on BGI in Ethiopia, where the subject remains underexplored.

• We assessed the efficiency of two case green infrastructures (GIs) in reducing peak flows and substituting water supplies.

• The three points approach was used to assess the efficiency of case GIs in day-to-day, design, and extreme domains.

• Peak flow was reduced by as much as 79% in the immediate localities of the GIs.

• Up to 27% potable water supply substitution efficiency was found in some scenarios.