Page - 647 - in Book of Full Papers - Symposium Hydro Engineering

outages for reservoir emptying and removal of deposits by earthmoving equipment would cause high energy generation loss and accordingly revenue losses that rendered this method also not economically viable. Following table presents analyzed and evaluated management options that could be technically and economically feasible. Table 1 Specifications of evaluated sediment management techniques Method Specifications Flushing water level drawdown 25 m (Pool elevation @ 523 masl) Flushing discharge 40 m³/s Duration 12 hours after water level drawdown Frequency 1 flushing event per year Dredging Sediment concentration 30% deposits removed per dredging event 115000 m³/ event Frequency Continuous dredging operation HSRS Available head 33 m Pipeline length & diameter 3000 m & 1 m (one pipe) Sluicing water level drawdown 6 m Pool elevation @ 542 masl Duration of sluicing 6 months Frequency Annually Sediment Inflow Reduction Reduction of sediment inflow 30% of MAS (exclusion of sand and coarse silt) Maintenance Annual sand mining of RESCON-2 indicated that a hydrosuction removal system as specified in the table above would have a deposit removal capacity of approximately 90,000 m³/a with a continuous slurry discharge release of 2.5 m³/s. The associated water losses would be therefore considerable and would reduce the reservoir firm water yield. Furthermore, the necessary pipeline length of 3 km is marginally at the feasible applicability limits. Therefore, this technique can’t be applied the first years of reservoir operation, it is however a method that could be implemented later in the future. When the trap efficiency drop will reduce the annual deposits, a smaller HSR system will be able to maintain the storage in a sustainable manner. Following the technical feasibility criterion for density current venting that was developed by Morris and Fan (1998), RESCON-2 indicated that the appearance of density currents is plausible. The initial geometry of the reservoir will have as result however the dissipation of the density currents before they arrive at the low-level bottom outlet. Therefore, the venting, i.e. the release of density currents downstream of the reservoir will not be possible, at least the first years of reservoir operation. The progressive propagation of the deltaic deposits downstream will 647