River Flood Modelling for Nzoia River Basin, Kenya: a quasi-2D approach

摘要

This paper describes an application of integrated technique for flood modelling and mapping using geographical information systems (GIS) and hydrodynamic modelling. This was carried out using a quasi-2D flood modelling approach. A quasi-2D model has been set-up using the river modeling software MIKE 11/MIKE GIS for the dyked lower reach of Nzoia River (about 25km), close to Lake Victoria, Kenya. The hydrodynamic model implementation has been done for the main river and for the floodplains. The quasi-2D approach was used to model the floodplains as a network of fictitious river branch and spills with the main river. The developed quasi-2D flood model was used in conjunction with the digital elevation model (DEM) for the study area, which is flood-prone, to simulate the historical flood event of year 2008. The accuracy of the model was evaluated by use of a scatter plot, whereby elevations of points along the boundary of the historical and simulated flood extents were used and a correlation coefficient (R~2) of 0.8 of simulated versus observed elevations was achieved. The results show that the quasi-2D approach can be successfully used to model and map the spatial extent of a food event in such low lying dyked area. The method provides a good balance between accuracy and computational cost.