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1 Komi, K.; Neal, J.; Trigg, M. A.; Diekkruger, B. 2017. Modelling of flood hazard extent in data sparse areas: a case study of the Oti River Basin, West Africa. Journal of Hydrology: Regional Studies, 10:122-132. [doi: https://doi.org/10.1016/j.ejrh.2017.03.001]
Weather hazards ; Flooding ; Forecasting ; Hydrology ; Models ; Calibration ; Simulation ; Performance evaluation ; Rainfall-runoff relationships ; Satellite observation ; Remote sensing ; River basins ; Floodplains ; Case studies / West Africa / Oti River Basin
(Location: IWMI HQ Call no: e-copy only Record No: H048094)
http://www.sciencedirect.com/science/article/pii/S2214581817300757/pdfft?md5=b29831cd1e8f2bbfc9b9d2dbdebcdcce&pid=1-s2.0-S2214581817300757-main.pdf
https://vlibrary.iwmi.org/pdf/H048094.pdf
https://vlibrary.iwmi.org/pdf/H048094.pdf
(1.59 MB) (1.59 MB)
Study region: Terrain and hydrological data are scarce in many African countries. The coarse spatial resolution of freely available Shuttle Radar Topographic Mission elevation data and the absence of flow gauges on flood-prone reaches, such as the Oti River studied here, make flood inundation modelling challenging in West Africa.
Study focus: A flood modelling approach is developed here to simulate flood extent in data scarce regions. The methodology is based on a calibrated, distributed hydrological model for the whole basin to simulate the input discharges for a hydraulic model which is used to predict the flood extent for a 140 km reach of the Oti River.
New hydrological insight for the region: Good hydrological model calibration (Nash Sutcliffe coefficient: 0.87) and validation (Nash Sutcliffe coefficient: 0.94) results demonstrate that even with coarse scale (5 km) input data, it is possible to simulate the discharge along this region’s rivers, and importantly with a distributed model, derive model flows at any ungauged location within basin. With a lack of surveyed channel bathymetry, modelling the flood was only possible with a parametrized sub-grid hydraulic model. Flood model fit results relative to the observed 2007 flood extent and extensive sensitivity testing shows that this fit (64%) is likely to be as good as is possible for this region, given the coarseness of the terrain digital elevation model.
Study focus: A flood modelling approach is developed here to simulate flood extent in data scarce regions. The methodology is based on a calibrated, distributed hydrological model for the whole basin to simulate the input discharges for a hydraulic model which is used to predict the flood extent for a 140 km reach of the Oti River.
New hydrological insight for the region: Good hydrological model calibration (Nash Sutcliffe coefficient: 0.87) and validation (Nash Sutcliffe coefficient: 0.94) results demonstrate that even with coarse scale (5 km) input data, it is possible to simulate the discharge along this region’s rivers, and importantly with a distributed model, derive model flows at any ungauged location within basin. With a lack of surveyed channel bathymetry, modelling the flood was only possible with a parametrized sub-grid hydraulic model. Flood model fit results relative to the observed 2007 flood extent and extensive sensitivity testing shows that this fit (64%) is likely to be as good as is possible for this region, given the coarseness of the terrain digital elevation model.
2 Bekele, Tilaye Worku; Haile, Alemseged Tamiru; Trigg, M. A.; Walsh, C. L. 2022. Evaluating a new method of remote sensing for flood mapping in the urban and peri-urban areas: applied to Addis Ababa and the Akaki Catchment in Ethiopia. Natural Hazards Research, 2(2):97-110. [doi: https://doi.org/10.1016/j.nhres.2022.03.001]
Flooding ; Mapping ; Remote sensing ; Urban areas ; Periurban areas ; Catchment areas ; Satellite imagery ; Polarization ; SAR (radar) ; Datasets ; Land use ; Land cover / Ethiopia / Addis Ababa / Akaki Catchment
(Location: IWMI HQ Call no: e-copy only Record No: H051312)
https://www.sciencedirect.com/science/article/pii/S2666592122000130/pdfft?md5=33390119e761bbcbf93233450d6d72df&pid=1-s2.0-S2666592122000130-main.pdf
https://vlibrary.iwmi.org/pdf/H051312.pdf
https://vlibrary.iwmi.org/pdf/H051312.pdf
(7.90 MB) (7.90 MB)
The Sentinel-1 SAR dataset provides the opportunity to monitor floods at unprecedentedly high spatial and temporal resolutions. However, the accuracy of the flood maps can be affected by the image polarization, the flood detection method used, and the reference data. This research compared change detection and histogram thresholding methods using co-polarization (VV) and cross-polarization (VH) images for flood mapping in the Akaki catchment, Ethiopia, where Addis Ababa city is located. Reference data for the accuracy assessment were collected on the satellite overpass date. A new method, Root of Normalized Image Difference (RNID), has been developed for change detection. Multi-temporal flood maps using the best performing method and image polarization were generated from April to November of 2017–2020. Better accuracy was observed when using the RNID method on the VH polarization image with an overall accuracy of 95% and a kappa coefficient of 0.86. Results showed that flooding in the Akaki commonly begins in May and recedes in November, but flooding was most frequent and widespread from June to September. Irrigated land and built-up area accounted for 1057 ha and 544 ha of the inundated area, respectively. Several major roads in the study area were also affected by the floods during this period. Our findings indicate that the S-1 images were very useful for flood inundation mapping, the new change detection method (RNID) performed better in urban and peri-urban flood mapping, but the accuracy of the flood map significantly varied with the flood detection method and the image polarization.
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