Author(s): Alexandra M. Murray; Henrik Garsdal

Linked Author(s): Alexandra Murray

Keywords: Flood reduction; Nature-based solutions; Sediment budgeting; Sediment management; Sediment modelling

Abstract: River flooding on the Shabelle River in Somalia has increased, in large part due to sediment deposition in the river between Beledweyne and Jowhar. An initial sediment source analysis shows that 95% of sediment entering the river system originates upstream of Beledweyne in the Ethiopian portion of the Shabelle catchment. To inform application of Nature-based Solutions to stabilize embankments and prevent topsoil erosion, a 1D hydraulic model was developed and used for scenario testing. It was determined that reduction of upstream sediment load did not significantly impact river flooding, but that reduction of eroded topsoil from Somalia greatly impacted sediment deposition. Deposition was decreased by 44% and 85% by decreases of 25% and 50% of the topsoil erosion source respectively. Elimination of the topsoil erosion source shifted the river from a depositing to an eroding system, further indicating that focus on retention of topsoil, for example by nature-based solutions such as reforestation initiatives, could have profound impact on the river system and be effective to reduce flooding. Unique to this work is the severe data and interaction limitations due to conflict in Somalia. A wide variety of data sources were used to produce the 1D hydraulic river model and the scope of the investigated scenarios were appropriate for the data limitations. This study is instrumental to focus further work and monitoring campaigns and to ensure efficient utilization of the limited resources in the region to reduce flooding and better the lives of the citizens of the Shabelle River basin.

DOI: https://doi.org/10.3850/978-90-833476-1-5_iahr40wc-p0199-cd

Year: 2023