Sedimentation in reservoirs Tana River Basin, Kenya. III - Analysis of Hydrographic surveys of three reservoirs in June/July 1983. Part A

Wooldridge, R. (1984) Sedimentation in reservoirs Tana River Basin, Kenya. III - Analysis of Hydrographic surveys of three reservoirs in June/July 1983. Part A. Technical Report. HR Wallingford.

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Abstract

A research project to develop methods of predicting rates of sediment deposition and distribution in tropical reservoirs is currently being undertaken at Hydraulics Research, Wallingford, using funds made available ~ by the Overseas Development Administration of the British Foreign and Commonwealth Office. The project involves data collection from sites in Kenya, Indonesia and the Philippines. A collaborative investigation was started in Kenya in 1980 to study the distribution of sediment within two, and more recently three, reservoirs on the Tana River, and to monitor the transport of suspended sediment by rivers feeding these reservoirs. The collaborative organisations - the Tana and Athi Rivers Development Authority, the Ministry of Water Development and the Kenya Power and Lighting Co Limited - are providing finances and staff to cover the Kenya end of the investigation. The first stage of the investigation was to produce a set of base data against which all future reservoir surveys will be compared. These data, which were abstracted from an aerial survey flown in 1965, are described in HR report OD 45. An hydrographic survey was carried out in June/July 1981 and a number of analytical methods were tried on the results obtained. Details of these are given in HR report OD 46. In June/July 1983, a second hydrographic survey was run and this time it included !1asinga reservoir. Data were also collected on in-situ bed densities. A modification of the analytical method chosen in report OD 46 has been used but with refined input data. The results indicate that Kamburu reservoir capacity has been reduced by 11.7% since its impoundment in 1974 and Kindaruma has lost 38.8% since 1968. Deduced catchment sediment yields show an annual increase of 2% averaged over the whole period from 1968 to 1983. Limitations on the accuracy of such deductions are explained and a comparison is made with trial catchment data recorded in Malawi.

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