Impact of Flow Rate, Sediment Uniformity, and Outlet Size on Sediment Removal Upstream of a Cross-River Structure

The sediment accumulation behind dams and cross-river structures reduces storage capacity, increases pool water level, reduces hydropower production, and causes damage to the blades of turbines. The operation of the impoundment hydropower and run-of-river plants is affected by the sediment accumulation in the vicinity of their water intake. In this study, the effectiveness of sediment removal through an outlet in a model of cross-river structure was experimentally investigated. The model was fixed tightly at the end of a 2 m working section in a laboratory flume with a length of 12 m, a width of 0.3 m, and a depth of 0.45 m. To study the impact of main variables on scour volume (Vs), a total of 27 experiments were conducted. The studied variables were flow rate (Q), area (Ao), location of outlet centerline outlet from the bed (hs), and uniformity of the sedimentation used in the mobile bed of the working section. For the same outlet area (Ao = 47.5 cm2), results show that when the flow rate increased from 3.2 to 6.3 l/s, the scour volume in nonuniform sediment was increased by twofold. However, the above increment caused the scour volume in uniform sediment to increase by only 170%. In addition, the scour volume in the mobile bed of uniform sediment was found to be greater than that in nonuniform sediment by an average of 17%. For a flow of 3 l/s and when the outlet area was reduced by either 25% or 50%, the scour volume in both uniform and nonuniform sediment was reduced by 46%. The accuracy of the proposed dimensionless multiregression model was statistically tested by calculating the Nash efficiency coefficient (NEC) and found to be 0.91, which confirmed the accuracy of the model prediction. The outcomes of the present study are useful to engineers involved in dam design and management.