Developing Feasible Structural Flood Mitigation Measures for Arid Regions Using Hydrological and Hydraulic Modelling: a Case of Baledweyne City, Somalia

Abstract

Flood mitigation measures are essential in several aspects of environmental sustainability, such as environmental protection and development, infrastructure resilience, and climate change adaptation strategies. This study investigates several remedial measures such as flood and disaster risk reduction strategies to protect Baledwayne City, Somalia. The developed hydrological-hydraulic model is successfully calibrated using the 2019 flood event. Inundation maps for different mitigation measures are developed to determine the most appropriate one(s) that may reduce flood impact and protect the city, especially the residential areas, against peak discharge of a 500-year return period. The investigated mitigation measures include (1) operating the Warabole Diversion Canal, (2) building two detention ponds at the upstream sections of both right and left floodplains, (3) building levees (dikes) along both sides of Shabelle River, and (4) restoration of the river. Results show that the remedial measures for the Warabole Diversion Channel and the river restoration are insufficient to protect the city. Building ponds on the right- and left-hand sides of the river substantially protects the city from flooding by reducing the flooded area from 88.6 to 31.5 km2, which is equivalent to a reduction of 35.5%. Construction of dikes on both sides of the river does not protect the city by overflowing an area of 75.2 km2 (84.9%). A combination of several measures is also investigated and it is found that ponds must be built along with any alternative measure. When all four measures are combined, it becomes clear that the city's residential areas would be fully protected, significantly reducing the overall flooded area of the city to 27.9 km2 (31.5%). These flooded areas are behind the detention pond, which is designed to hold floodwater and gradually drain it back to the river.