Catchment Rain Water Harvesting: Evaluation Of Ground Water Storage Capacity By In- Stream Sand Storage Dam Construction In Kitui District, Kenya
Munyoki, M Joseph
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Sand storage dams have been observed to be able to meet the integrated water requirements in the arid Kitui district. This has been through various studies that have reported increased water availability in the catchments developed with the sand dams. This study looks at the causes of this increased amount of water in the stream channel. Among the major study parameters include the storage capabilities of sand storage dams. This includes the channel storage, bank storage capabilities, and the fluctuation in water levels both in time and in different section of the stream channel in relation to position of the sand dam. This is in relation to precipitation episodes in the catchment. The distribution of the sand dams in the catchment was also mapped to show the convenience of water points. This showed great reduction to the distribution of water points in terms of distances. The volume of sand column in the river mapped using a dipping rode to show the storage capacity in the stream channel. There was a large volume of sand which resulted from the installation of the dam wall. This acted as an aquifer that stored water abstracted by the dam. In the banks, remarkable raise in water levels observed from installation of piezometers. Monitoring of the fluctuations with time was also observed with water levels raising and falling with subsequent precipitation episodes. This was both in the stream channel and in the banks of the river. Measurements were carried out in both the wet and the dry season. Rainfall was measured with piezometers placed in strategic places in the catchment. This was to compare the rainfall events with the fluctuation of the water levels. Discharge of the stream was also determined at the study dam in relation to rainfall intensity measured by a tipping bucket placed on the upstream section of the dam. Surface evaporation was compared from subsurface. evaporation from the sand. There was a great reduction in the amount of water losses due to-evaporative processes . .• Electrical conductivities were measured along the stream channel using a hand held electrical conductivity meter. There was a remarkable variation in these both in space and time over the periods of the study and in different sections of the study profile. '" The general conclusion of the study is that the sand dams greatly increased the storage capacity of the stream channel, big volumes of water was also stored in the banks. It is also observed that the river recharged the banks during the rainy season and the vise versa happened in the dry season when the water levels in the channel are lowered, the flow is reversed. Hence the banks act as buffers for the stream in the dry season. Evaporative losses were greatly reduced by storing the water below the surface. This was determined by comparing the surface evaporation with evaporation from the subsurface below the sand.