ABSTRACT
The water control goal for constructing Kubanni reservoir in 1973 is threatened by accumulation of sediments in it as a result of its design, anthropogenic activities on some parts of its catchments' area and the highly erosive nature of the soil type in the basin. To improve on the effective management of the Kubanni Reservoir, sedimentation in the reservoir was investigated from June to December, 2006. Total sediment discharged into the reservoir was quantified at two gauging stations located on the two inflowing rivers. The daily suspended sediments were determined from models developed from actual measurements of sediment concentration and water discharge, while daily bed loads were estimated from models based on Colby empirical relations. The total sediment input of 20,387 tonnes/year was estimated and used to determine the useful life of the reservoir, which was found to be 107 year. Also, the depth of the reservoir was surveyed using a weighted line from a small boat. The result revealed that Kubanni Reservoir had lost 48% (1.26 x 106 m3) of its initial volume (2.6 x 106 m3) to sedimentation in 33 years of operation. This implies that the reservoir had undergone serious sedimentation loading in the past and an estimated useful life of 107 years is no more feasible. Having the reservoir volume depleted close to half necessitates improved drastic control measures than ever before to forestall sedimentation in the Kubanni watershed. Recommendations made on actions to be taken to forestall sedimentation in the reservoir are dredging, surveillance, construction of sediment retention basins and planting of carpet grasses.