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

ABSTRACT 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% local and 41.32% watershed-scale peak flow attenuation. Watershed-Scale 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.