Temporal and spatial dynamics of surface run-off from Lake Basaka catchment (Ethiopia) using SCS-CN model coupled with remote sensing and GIS

The Lake Basaka catchment (Ethiopia) has undergone a significant land use–land cover (LULC) change and lake level rise over the past five decades. Significant quantities of water and sediment flow annually into the lake through erosion processes. An appropriate method of estimating the surface run-off from such ungauged and dynamic catchment is extremely important for delineating sensitive areas (based on run-off responses) to be protected and for development of suitable measures to reduce run-off and associated soil loss. Reliable prediction of run-off, however, is very difficult and time-consuming for catchments such as that of Lake Basaka. The present study estimated the dynamics of surface (direct) run-off using the NRCS-CN model in ArcGIS, assisted by remote sensing and ancillary data. The results indicated the Lake Basaka catchment experienced significant temporal and spatial variability in its run-off responses, depending on the rainfall (amount and distribution) pattern and LULC changes. A significant run-off increase occurred after 1973, consistent with significant LULC changes and lake level increments occurring after that period. A reduced vegetation cover also resulted in increased run-off coefficient of the lake catchment from 0.11 in the 1970s to 0.23 in the 2000s, indicating the important need to consider possible future LULC evolution when forecasting the lake catchment run-off behaviour.