Replication data for: Simulating impact land use change watershed services in Sasumua Watershed using SWAT

Land use change has a major influence on the capacity of watersheds to produce watershed services such asimproving water quality and flood mitigation. The objective of this study was to simulate the effect of land usechange on the sediment and water yield in Sasumua watershed, Kenya using SWAT model. The SWAT modelwas calibrated and validated using recorded reservoir data. The validated model was then used to simulatewater and sediment yield under three scenarios of runoff curve number CN (improved land surface conditionCN-6, base case, degraded land surface condition CN+ 6). The CN was used as a surrogate to represent landsurface treatments that influence generation of surface runoff following rain events. The coefficient ofdetermination from the calibration of the model was 0.6 and 0.5 for the validation. An increase in CN by 6(scenario CN+ 6) units in the agricultural part of the watershed, increased the sediment loading to the streamsby 53.6% while a reduction by 6 units (scenario CN-6) reduced sediment loading by 34.3%. Scenario CN-6resulted in a 28.5% decrease in surface runoff, a 13.8% increase in base flow and a slight decrease in totalwater yield of 1.2%. On the other hand, scenario CN+ 6 increa sed the surface runoff by about 44%, reducedbase flow by 10.5% and increased the water yield by 6.5%. Improvement in land surface condition thatenhances infiltration is a feasible conservation measure to reduce soil erosion and subsequent sedimentation ofthe rivers and the reservoir. CN-6 can be achieved through terracing, contour farming, grass strips, better cropresidue management and well managed grazing