Investigation of Dominant Hydrological Processes in Chania Catchment at a Temporal Scale

This study investigates the dominant hydrological processes governing the temporal variability of stream flow in Chania catchment. The study area is located within the upper Tana catchment which is the main source of Nairobis water and hydropower supply downstream. The hydrology of this area is poorly understood because of inadequate information due to the ungauged nature of the catchment. Temporal dynamics of parameter sensitivity of the Soil and Water Assessment Tool was used to achieve this objective. The results show that the parameter sensitivity varies temporally. High sensitivity for two groundwater parameters, (base flow recession constant and groundwater time delay), one soil factor (available soil water capacity) and one evaporation parameter (soil evaporation compensation factor) were observed. The soil evaporation compensation factor dominates in re-saturation and baseflow segments of the streamflow hydrograph while, groundwater time delay and base flow recession constant are dominant during the peak and recession segments. Flow duration curves (FDC) were also used to relate sensitivities to certain magnitudes of streamflow. Runoff parameters were mostly sensitive in the Q0-Q5 segment while evaporation parameters are mostly sensitive in the Q5-Q20 and Q20-Q70 segment of the FDC. Highest sensitivities of two ground water parameters (base flow recession constant and ground water time delay) are detected in Q70-Q95 and Q95-Q100 ( low flow) segments