Mitigating Perennial Floods in Cities of the Global South: A Nature Based Approach

Abstract

Abstract The incidence of flooding in cities of the global south has become perennial with increasing urbanization, showing a lack of targeted approach to the challenge. The objective of this research was to develop a resilient and an integrated approach to stormwater management that could be used to inform policy. The Research for Design model was adopted using the Greater Accra Metropolitan Area (GAMA), Ghana as a case. Land cover types for three focal areas; Area1, Area2, and Area3, respectively 10.2 km2, 10.2 km2 and 10.5 km2 were extracted and combined with daily rainfall values to estimate direct runoff, using the Curve Number method. Eight [8] landcover types were extracted based on which percentage imperviousness was determined for Area1 (54.1%), Area2 (43.66%) and Area3 (22%). Area3 had more large roofs (≥ 81m2) averaging 248.5 m2 compared with Area2 (195.6 m 2) and Area1 (182.2 m2) but did not significantly impact runoff generation at 5%. Harvestable roof runoff for both small roofs (< 81m2) and large roofs (≥ 81m2) contributed 32.6% in Area1, 22.5% in Area2 and 14.7% in Area3, to runoff generation per rain event. The results suggests that retaining roof runoff at the plot level could significantly reduce stormwater runoff. To demonstrate this Living Labs concepts was combined with various design methods, aided by a schema to integratively design a selected site for roofwater harvesting for irrigation, storage for non-portable uses, infiltration to recharge groundwater and to create amenity values. The research contributes to knowledge by proposing a quantitative basis to target stormwater management at the plot level.