Evaluating the Performance of Low-Impact Development Practices in Mitigating Runoff Floods in the Kinyerezi River Catchments in Dar es Salaam, Tanzania

The impermeable areas in catchments are proportional to peak flows that result in floods in river reaches whose flow-carrying capacity is inadequate. Urbanization is the major factor contributing to floods and intensifying flood risks in urban areas. Dar es Salaam city experiences frequent floods along the Msimbazi River likely due to urbanization. The Low Impact Development (LID) practices that include bioretention (BR) ponds, rain barrels (RB), and rain gardens (RG) have the potential to reduce peak flows and flood levels. This study aims to evaluate the performance of BR, RG, and RB in mitigating peak runoff floods in the Kinyerezi River catchment using the SWMM model. A total of 3698 RB each with 3000 L capacity, 3698 RG each with 28 m² and 0.9 depth, and 101 BR ponds of sizes ranging from 800 to 10,000 m² each with 1.2 m depth were deployed into the sub-catchments. The results indicated that the combination of BR, RG, and RB reduced the peak runoff flows and volumes by 36.8% and 24%, respectively. The combination of the three LID practices offered the best performance in mitigating peak runoff floods. It was recommended that authorities should encourage city residents to practice households’ RB and residential RG at the household level. In addition, city planning authorities should ensure that open spaces are left in residential areas for the construction of BR ponds in the future.