RESERVOIR SEDIMENTATION: THE CASE OF THE OPA RESERVOIR CATCHMENT, SOUTHWESTERN NIGERIA

Abstract

ABSTRACT This study aimed at determining the rate of sedimentation in Opa Reservoir since impoundment in 1978 with a view of ascertaining how much of its volume has been silted up. The volume of sediment trapped in the reservoir since impoundment was estimated using the bathymetric survey method. Based on reservoir profiling, the volume and mass of deposited sediments since impoundment in 1978 were estimated at 1 313 397m3 and 893 096 tonnes, respectively. The rate of sedimentation and specific sediment yield from the reservoir catchment were estimated at around 38 000t/yr and 575t/km2/yr, respectively. The annual rate of sedimentation obtained in this study highlights the need for more frequent bathymetric surveys especially after large floods to provide more information on the magnitude of annual sedimentation, and to help planners determine how to prolong the economic life of reservoirs.