Evaluating the hydraulic capacity of existing drain systems and the management challenges of stormwater in Addis Ababa, Ethiopia

Study region: Addis Ababa, Ethiopia. Study focus: Addis Ababa is undergoing rapid urbanization with unprecedented high rate of road and building constructions, resulting in a sudden upsurge of sealed surfaces and generation of significant amounts of stormwater. The present study therefore aims to investigate the hydraulic capacity of existing drains and stormwater management challenges using detailed field surveys, and stakeholders' interview. 469 road segments (74 km) and 202 drain segments (42.76 km) in two representative case sites confined in 564.54 ha boundary areas were physically surveyed. New hydrological insights for the region: Results showed that 14% of the drains in new city parts and 28% in old city parts were in conditions inadequate for removal of stormwater, resulting in flash flooding and infrastructure degradation in the associated watersheds. Further, although more than 72% of the surveyed drains were oversized, stormwater overtopping reoccur as a season-to-season problem, ascribed to illegal dumping of waste into drains, reducing their hydraulic capacity. The challenges of stormwater management were related to lack of city-wide drainage master plan, absence of hydrologic data considerations during designing drains, and weak enforcement on solid and liquid waste dumping into drains. The present study recommends that building practices that minimize surface sealing and critical hydrologic and hydraulic considerations during designing drains, and educating the local community and stakeholders regarding waste management.