Water balance of sections of Naro Moru river
This water balance study is directed towards the solution of problems resulting from the utilization of river water resources for domestic purposes and for irrigation by ·small-scale farmers living on the semi-humid to semi-arid footzone and the semi-arid savannah regions of Naro Moru river basin and its effect on the residual discharge reaching river Ewaso Ng'iro. The study was carried out in two reaches of Naro Moru river located in the footzone and savannah areas of the basin. The study entailed making an inventory of water supply points along Naro Moru river, determining the amount of water abstracted from each water supply point over a period of six months, comparing the actual abstractions with the authorized abstractions, measuring river discharge at the river gauging stations marking the ends of each reach, and using a river reach water balance to estimate groundwater inflow into reach, transmission losses within reach and direct runoff contribution to reach. The aim of the study was to find out how streamflow is affected by each of the factors mentioned above as a prerequisite for recommending ways of improving the water allocation and management. On a monthly basis, the amount of water abstracted from each reach as a percentage of river inflow into reach was about 10 % in the foot zone and savannah during the short rains season (November and December) and rose during the dry season up to 35 % in February and 47 % in March for the footzone and savannah reaches respectively. Community water supply projects which increased by four over the six year period from 1984 were responsible for about 97 % of the water abstracted from the river. Authorized abstractions constituted about 8 % of the measured dry season abstractions p.nd 30 % of the measured wet season abstractions. During the short rains in November and December, the footzone river reach received additional flow from groundwater sources and from direct runoff while the savannah river reach lost water on transmission possibly due to infiltration into the riverbed and sides during high flows. Release of groundwater into the foot zone river reach continued into the dry month of January and transmiss ion losses for both reaches were lower over the ensuing dry season (January to March). The long rains season resulted in the addition of direct runoff into the two reaches but the effect was more pronounced in the savannah than in the footzone. This may be explained by the fact that the soils in the savannah region swell on wetting thus reducing the rate of infiltration while those in the footzone have generally higher rates of infiltration. Proper assessment, allocation and management of the available river water may be achieved by installing simple structures to measure the amount of water diverted especially at the head of community water supply conveyance systems, maintaining a stricker control over the issuing and renewal of water permits and improving the efficiency of water use.