Evaluation of Sediment Concentration and Turbidity of two Tributaries of Oyan Dam Reservoir

— Reservoir sedimentation is an important consideration for dams and reservoir integrity. Soil particles eroded from congruent catchments are usually deposited into reservoirs built for impounding water for different purposes. This study evaluated the sediment concentration and turbidity in Ofiki and Oyan rivers, south-west Nigeria. Sampling was done on the two rivers using equal-width-increment method between October 2020 and Septembers 2021. Results indicated that sediment concentrations range from 38.17- 401.67 with a mean value of 186.4 mg/L, and 9.67 – 421.75 mg/L with a mean value of 167.23 mg/L for Ofiki river and Oyan river, respectively. Turbidity ranged from 0.20 – 95.35 NTU with a mean value of 25.54 NTU and 0.01 – 83.90 NTU with a mean value of 18.92 NTU for Ofiki river and Oyan river, respectively. Simple linear regression of both parameters gave regression models C_(s^( = ) ) 85.26T^0.26 with R^(2 )=0.42 for Ofiki and C_s=3.95+92.48 with R^(2 )=0.51 for Oyan river. Turbidity and sediment were found to be higher during the raining season, and higher in Ofiki river than Oyan river