Assessing Changes on the Floodplain of Sandy Rivers Using Geospatial Techniques; Case of Athi Sub-Catchment in Makueni

Degradation of floodplains by land-use pressures requires sustainable management and conservation measures to protect them. Delineating and mapping changes which have occurred in such ecologic valuable areas is important in planning those measures. GIS and remote sensing techniques have been utilized in this study to delineate and assess the changes which have occurred on the floodplain of sandy rivers in Athi sub-catchments. The study is concerned within three sub-catchments found in Makueni County. This area is semi-arid and experience water resources challenges. The use of sand dams on the seasonal rivers is common in the area. A geomorphological approach which uses DEM, slope and stream network has been used to delineate the floodplain. Landsat TM and ETM+ images of 1986, 1995, 2002 and 2011 has been used to do land cover classification of the floodplain. Four land cover classes dense vegetation, sparse vegetation, wetland and sand were identified. In this study, change detection shows that dense vegetation on the floodplain has decreased over the years, mostly to sparse vegetation. There is also an increasing trend of sandy land and notably most of the wetland has changed to sand over the years.