Assessing the effect of land-use change on the flow region of River Rwizi

Abstract

River Rwizi has over the years been facing drastic changes in its flow regime. The occurrence of low stream flows in the dry season and high peak flows in the wet season has been common. This phenomenon has not been widely researched about in relation to the changes in land uses in the catchment area using hydrological models. This study was specifically aimed at determining the reliability and usability of the stream flow data of the river, setting up, calibrating and validating the HBV model for the Rwizi catchment as a tool for studying the effect of land use changes on the river’s flow regime. The response of stream flows to land use changes was also studied. ArcGIS was used to generate the land use-cover maps from Landsat acquired in the year 1987, 1997 and 2007 respectively using the Maximum Likelihood Algorithm of Supervised Classification. The penman monteith equation was used for calculating evapotranspiration and the Nash and Sutcliffe coefficient (NSE) was used as the objective function for determining model performance. The model calibration and validation processes gave NSE values of 0.78 and 0.71 respectively. The results of land cover change detection and annual average stream flow showed a strong relationship. This was supported by the analysis of two scenarios created by using two different land use sensitive model parameter sets for the period 1998-2007. The model’s simulated stream flow values in both scenarios were graphically compared. The stream flow data obtained from the gauging station was found to be reliable and usable. The model was successfully set up, calibrated and validated for the catchment area. From the graphical comparison of the simulated flows of the two scenarios for 19982007, the changes in land use sensitive parameters resulted in a general decrease of the stream flows showing a strong relationship between the two. The relevant authorities such as NEMA should intervene and enforce better communitybased land management policies to curb the land cover change problem in the Rwizi catchment. Integrated Water Resource Management should be effectively implemented at all levels. More research on land cover changes in the catchment should be done using other models and methods.