Author(s): S. M. C. K. Subasinghe; K. B. Akalanka Silva; K. P. P. Pathirana; L. V. Talagala; K. Raveenthiran; Veloo Chandrasegaran
Keywords: Nnual sediment load; Discharge; Brune curve; Sediment rating curves; Fluvial sediment monitoring program
Abstract: Sedimentation is the single process that all reservoirs worldwide share in common. Further, sediment management is very important for any reservoir where sustainable long-term use is to be achieved. The objective of this study was to monitor the loading of suspended sediment in Kotmale Oya in Upper Kotmale Basin specific to selected locations in Agrapathana Oya, Nanu Oya, Talawakele Intake Dam and Tailrace tunnel through a fluvial sediment monitoring program on monthly frequency. Sediment rating curves were developed for both Nanu Oya, Agrapathana Oya catchments and for entire Upper Kotmale basin to obtain corresponding sediment concentrations for different discharges. The estimated average annual sediment load to the dam site is 11,549 tons/yr whereas the estimated annual suspended sediment yield from Upper Kotmale Basin is 0.39 tons/ha/yr. These estimations are highly affected by the factors such as rainfall, catchment slope, land use pattern and soil type etc. Moreover, the estimated approximate sediment outflow through turbines are more than 75%and long term trap efficiency from Brune Curve is 32%with an expected reservoir capacity reduction of 0.05%to 0.1%per year. The main conclusion of the study was that the sediment load from the catchment is not very high and risk of the reduction of reservoir active storage capacity due to siltation is very low.