Seite - 651 - in Book of Full Papers - Symposium Hydro Engineering

and reduction of sediment inflow though construction of a sediment trap upstream of the reservoir is presented in the table below. Table 2 Evaluation of technically feasible sediment management techniques Method Long-term capacity Water and energy losses Env. Impacts CAPEX O&M Flushing ++ - - - - 0 - Dredging +++ - - - - - - - - - - Sluicing + - +++ 0 - Sed.trap ++ +++ - - +++ The results indicate that dredging is the only method that can sustain the active storage at the pre-impoundment level. It is followed by flushing and the sediment trap that can preserve 50% of the pre-impoundment storage and finally by sluicing that will have as result a long-term active storage capacity ratio of 25%. Dredging and flushing however are excluded because they will increase the sediment concentrations downstream, endangering thus the fish habitat of Mahaweli River. Finally, the combined implementation of sediment trap and sluicing is the optimum solution because it has the best performance below dredging without the adverse environmental impacts. Sluicing can be implemented within a time horizon of 10 -15 years after the impoundment of Moragolla reservoir, while the sediment trap preferably should be in place by the time of the reservoir inundation. Having in mind the above indicated possibilities of the RESCON-2 model for a rapid assessment of different sediment management strategies as well as good agreement of its results with a widely used one-dimensional numerical model we could recommend it for further use in similar applications. REFERENCES [1] ANNANDALE, G.W., MORRIS, G.L., KARKI, P. Extending the Life of Reservoirs: Sustainable Sediment Management for Dams and Run-of-River Hydropower, The World Bank, 2016. [2] MORRIS, G.L., FAN, J. Reservoir Sedimentation Handbook, 1998 [3] ANNANDALE, G.W., Quenching the Thirst: Sustainable Water Supply and Climate Change, 2013 [4] PALMIERI, A., SHAH F., ANNANDALE, G. W., DINAR A. Reservoir Conservation, Volume I: The RESCON Approach, The World Bank, 2003 [5] EFTHYMIOU, N. P., PALT, S., ANNANDALE, G.W., KARKI, P. Reservoir Conservation Model RESCON 2 Beta - Economic and Engineering Evaluation of Alternative Sediment Management Strategies, User Manual, The World Bank & Fichtner, 2017 651