Page - 646 - in Book of Full Papers - Symposium Hydro Engineering

empirical methods and therefore sound engineering judgment is required for interpretation of the results. In terms of the Moragolla sedimentation study, the following sediment management techniques were analysed and evaluated.  No Action (i.e. No sediment management),  Reduction of sediment inflow by implementing a sediment trap upstream of the reservoir headwaters,  Deposit removal techniques, including flushing, dredging and trucking and HydroSuction Removal System (HSRS),  Sediment routing techniques, including sluicing, sediment by-pass and density current venting. 3.2. RESERVOIR LIFETIME FOR THE NO-ACTION SCENARIO The result of the numerical simulation of sedimentation for the available daily flow time series with duration of 43 years is plotted in Fig. 3 with black points. The black straight lines represent the time-path of the gross and active storage as calculated by RESCON-2. It was concluded that the service lifetime of the reservoir will be approximately 55 years, corresponding to a mean annual storage loss rate of approximately 2%. The overall good agreement between the results of HEC-RAS and RESCON- 2 with regards the gross storage development supports further the application of RESCON-2 for preliminary screening purposes of the available sediment management techniques. Unfortunately, HEC-RAS does not provide the possibility to plot the temporal development of the storage at different pool elevations. This prevented a comparison between the HEC-RAS and RESCON-2 results regarding the allocation of deposits between active and inactive storage respectively. Nonetheless, RESCON-2 indicated that the sedimentation of the active storage pool will commence immediately after the reservoir impoundment due to deltaic deposits at the headwater of the reservoir. 3.3. EVALUATION OF SEDIMENT MANAGEMENT OPTIONS The assessment of the technical feasibility of the available sediment management techniques and the corresponding temporal development of the reservoir storage has been performed with application of RESCON-2. The specifications of the evaluated sediment management techniques are given in the table below. The techniques of sediment by-pass and trucking were excluded because they were considered as not economically viable due to very high implementation or annual operation costs. In the case of sediment by-pass, the calculated costs for construction of an approximately 3 km long diversion tunnel were prohibitive for the implementation of this technique. In the case of trucking, the necessary 646