Three-dimensional computational fluid dynamics with sediment transport modelling in hydropower reservoir: the Binga study case in The Philippines

The Binga reservoir was rapidly filled with sediments due to an underestimation of the sediment load and the absence of any sediment management strategy. The Binga reservoir is gradually losing its remaining ability to regulate the flow of Agno river as the water storage capacity is reduced year by year due to sedimentation. The sediment inflow is expected to increase over the coming years because the sedimentation that takes place in the upstream reservoir, Ambuklao reservoir, and its associated reduction of sediment trapping efficiency will increase the sediment load released to Binga reservoir. Also, the Binga tributaries, Adonot/Leboy and Bisal rivers, carry very high sediment loads to the reservoir. The Binga reservoir will therefore lose most of its remaining flow regulating capacity and the sediment trapping ability approaches zero. Sediment management is crucial to maintain the plant as a run-of-river project. There must be provided a safe passage of floods, maintaining a sustainable ability to dampen the peak of the floods as much as possible, keeping the safety and integrity of the dam and the spillway, and the ability to produce power, providing always a safe passage of all incoming sediment loads. It is extremely important to stop the progression of the delta towards the intake, otherwise it can be clogged since the delta is more likely to develop a fan shape deposition pattern further in the direction towards the intake rather than the spillway. An alternative is proposed to direct the sediment load straight towards the spillway. It consists in the placement of a shortcut or canal in the right bank peninsula, considering the flow patterns in the first curve just before the peninsula. Simulations are carried out with SSIIM, for sediment transport evaluation after the implemented design. These evaluations will show if the canal will shorten the distance to the spillway with a straight path, thus avoiding the possible obstruction of the intake.