Page - 650 - in Book of Full Papers - Symposium Hydro Engineering

be characterized by lower sedimentation rate in the active storage and higher sedimentation rate of the inactive storage compared to the no-action scenario. On the long-term sluicing will be able to sustain only 10% of the gross storage. The impact however on the active storage will be substantially larger, and 25% of the initial active storage will be preserved sustainably. Sluicing however will not trigger the adverse environmental impacts that would follow flushing since the sediment routing will be synchronized with the ambient intra-annual variability of the sediment transport regime of the Mahaweli River. The performance of sluicing is substantially improved if it is combined with the sediment trap upstream of the reservoir. The combination of reduced and finer sediment inflow together with the water level drawdown during the high flow season intesifies the sediment routing out of the reservoir. This has as result a long-term capacity ratio for the active storage of 60%. The time path of the gross and active storage for this combination is plotted in Fig. 3 with dashed line. The detailed specification of the optimum sluicing operational rules will require a detailed assessment of the water, energy generation and revenue losses something that is out of the philosophy and the capabilities of RESCON-2. Based on the aforementioned results of the technical feasibility assessment, it was concluded that the only two techniques that can be implemented without important environmental disadvantages, are the reduction of sediment inflow through the construction of a sediment trap upstream of the reservoir headwaters and sluicing. Even more, it is concluded that the combination of the two methods will further improve the efficiency of sluicing and will reduce thus the associated energy generation losses providing sufficient space for further optimization. SUMMARY The Moragolla Hydro PowerPlant (HPP) project involves the implementation of a daily peaking Run-of-River Hydropower scheme in Sri Lanka. Numerical simulations indicated that the service lifetime of the reservoir will be approximately 50 years if no sediment management is applied, i.e. it will be non-sustainable. Furthermore, the active storage loss will affect the long-term economic performance of the facility. The recently developed software RESCON-2 was used for a rapid screening of the state-of-the-art sediment management techniques. The purpose was the selection and specification of the optimum sediment management solution considering the necessary tailoring onto the project specific boundary conditions that can convert the non-sustainable Moragolla reservoir into a sustainable infrastructure for the future generations. The economic viability assessment indicated that the costs or the water losses associated with the techniques of hydrosuction removal, sediment by-pass and trucking are prohibitive for their implementation. The technical feasibility assessment indicated that the technique density current venting at the moment is not applicable but it might provide an attractive option for the future. The comparative evaluation of the remaining methods, i.e. flushing, dredging, sluicing 650