KITUI SAND DAMS

decreases leading to a rise in the limp of the hydrograph. When the effective rainfall getsto the maximum, the hydrograph gets to the peak. The areas closest to the river contributeto the flow of the river first followed by the areas further upstream. This means that insmall catchments the peak is reached faster than in larger catchments.The boundary between the surface flow and the base flow is difficult to define anddepends on geological structures and composition of the catchment. Permeable aquiferslike limestone, and sandstone strata react faster than impervious clays. In one rainfallevent the base flow continues to flow even after the river levels have began to rise andonly when the storm has had time to percolate to the water table does the base flow beginto increase. This gets to its height at the end of the storm and thus accounting for thecontinual flow of the run off from the groundwater seepage. Groundwater provides thetotal flow of the general recession curve the next rainfall.Total flow.Peak flowRecession curveSurface run offRising limp Base flow. BDepletion curveATimeNegative base flow or bank storage.Components of a hydrograph.At the beginning of a rainfall event, the river discharge is low and a period of time lapsesbefore the river begins to rise.25