Unit Hydrograph:: Developing and Application of a Gis-based Spatially Distributed Unit Hydrograph (Sduh) Model for Runoff Water Harvesting in Small Watersheds

An SDUH model was developed using digital DEM elevation data and land use data collected during a field survey. The SDUH model was applied to a 5km2 agricultural watershed in the Upper Athi river region of the entire Athi river basin. The USGS DEM (30-m) resolution was used to estimate the slope, aspect, flow distance and upstream area for each cell. The watershed was divided into ?overland? and ?channel? flow cells based on the area upstream above each cell. If the area was larger than the threshold of 1.2km2 (1300cells), the cell was assumed to be dominated by channel flow. The flow velocity for the overland cells was estimated using a kinematic wave approximation. Channel velocities were predicted by estimating the channel dimensions and combining the equilibrium flow rate with Manning's equation. The cumulative travel time to the watershed outlet was estimated by routing runoff over the elevation surface and summing the travel time through each cell along the runoff flow path. The objectives of this research were to develop a SDUH model that directly reflects spatial variation in the watershed in generating runoff hydrograph.