Modelling of flood hazard extent in data sparse areas: a casestudy of the Oti River basin, West Africa

Abstract

Study region: Terrain and hydrological data are scarce in many African countries. The coarsespatial resolution of freely available Shuttle Radar Topographic Mission elevation data andthe absence of flow gauges on flood-prone reaches, such as the Oti River studied here, makeflood inundation modelling challenging in West Africa.Study focus: A flood modelling approach is developed here to simulate flood extent in datascarce regions. The methodology is based on a calibrated, distributed hydrological modelfor the whole basin to simulate the input discharges for a hydraulic model which is used topredict the flood extent for a 140 km reach of the Oti River.New hydrological insight for the region: Good hydrological model calibration (Nash Sut-cliffe coefficient: 0.87) and validation (Nash Sutcliffe coefficient: 0.94) results demonstratethat even with coarse scale (5 km) input data, it is possible to simulate the discharge alongthis region’s rivers, and importantly with a distributed model, derive model flows at anyungauged location within basin. With a lack of surveyed channel bathymetry, modellingthe flood was only possible with a parametrized sub-grid hydraulic model. Flood model fitresults relative to the observed 2007 flood extent and extensive sensitivity testing showsthat this fit (64%) is likely to be as good as is possible for this region, given the coarsenessof the terrain digital elevation model.