Abstract:
Human interference in the upper River Njoro catchment has led to the increased exposure of the land to
accelerated erosion. An application that combined the capabilities of remote sensing, geographic
information system (GIS) and agricultural non-point source (AgNPS) model was used to estimate peak
runoff rate and sediment yield from the upper River Njoro catchment. Remotely sensed Landsat
Thematic Mapper (TM) images were used to obtain land cover and associated AgNPS model input
parameters. Other input parameters for the model were extracted from GIS layers using the agricultural
non-point source-integrated land and water information system (AgNPS-ILWIS) interface. Surface water
quantity and quality data including peak runoff and sediment yield of selected storm events were
obtained from two gauging stations, within the catchment. Base flow separation was done so that
measured direct peak runoff rate and sediment yield generated by direct runoff could be determined
and compared directly with the model simulated results. Simulated peak runoff rates in Upstream
(Treetop) station were satisfactory with an EFF of 0.78 and a percent error of 4.1%. The sediment yield
was also reasonably estimated with an EFF of 0.88 and a 2% error. The downstream (Egerton) station
results were also satisfactorily predicted with peak runoff rate having an EFF of 0.69 and a 5.5% error of
estimates, while the estimated sediment yield had an EFF of 0.86 and a 2.5% error.
