Integrated flood modelling using open Lisem Model. A case study of Lubigi catchment area.

Abstract

Flood hazards are affecting a large number of the population worldwide. In Kampala, for various reasons floods are becoming more frequent and unpredictable and have had a negative effect on the lives of people, livestock, businesses, households and disrupted transport in various areas around Kampala. This study was carried out at Lubigi catchment area to obtain an understanding of flood duration and depth for the development of flood mitigation measures. This study aimed at using an integrated flood model (OpenLISEM) which takes into account of the whole study area as a cheaper and faster method than using the oftenly used methods of using ground observations which provide accurate information for a particular point but not for the whole catchment area. The objectives of the research were to determine the most sensitive parameters during the modeling process and then to finally provide the flood depth and duration maps. To obtain the flood depth and durations of the catchment area a landcover map, DEM, soil data, field interviews, rainfall data and drainage data were used. These were prepared in the PCRaster software which was installed in anaconda environment. From PCRaster the maps were imported in the OpenLISEM software which generated the flood depths and duration of the study area. The most sensitive parameter was obtained through sensitivity analysis using saturated hydraulic conductivity and initial soil moisture parameters. Saturated hydraulic conductivity was found to be the most sensitive parameter. This parameter was further used in the validation and calibration of the model. When the bias and RMSE were close zero, this was taken to be the final flood depth and duration maps. Consideration about finding the right value of saturated hydraulic conductivity (Ksat) is needed to optimize flood modelling. From the flood depth map, it was observed that the floods in the catchment area have a depth of up to 2 meters. Its also observed the floods have a duration of up to 38 hours after the rainfall events. In order to mitigate the floods events in the catchment area, I recommended the following; Improving the drainage system, roof top rain water harvest and drainage cleanliness.