Page - 649 - in Book of Full Papers - Symposium Hydro Engineering

result a drop of the trap efficiency of Moragolla reservoir which protects a large part of the active storage. The construction of the check dam will raise the water level in the river reach extending upstream of this structure by ≈2.5 m. Drainage pipes through the check dam will keep the reservoir upstream of the check dam lower during the dry season. The extent of the further inundation upstream of the check dam is expected to be approximately 2 km. If the width of the inundated area need to be confined, two lateral dikes along the river main channel shall be constructed. The necessary sand mining activity will cause an increase of the traffic in the local road network. On the other hand, this activity will reduce the transport distances for supplying sand, and may boost the local economy. Fig. 3 Storage development for the no-action scenario and the technically feasible sediment management techniques Sluicing over the spillway crest is technically feasible in Moragolla reservoir as long as a water level drawdown takes place when sediment laden flows enter the reservoir. The prediction of reservoir storage development with RESCON-2 indicated that the first ten years of reservoir operation sluicing will not change substantially the time path of reservoir gross storage because the sediment will be routed into the inactive storage and not out of the reservoir, since it will not be possible to overcome the barrier of the Moragolla dam. Sluicing however, will have as result an alteration of the spatial pattern of deposition in the reservoir which will 0 10 20 30 40 50 60 70 80 90 100 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 Years of operation No Action (RESCON-2) No Action (HEC-RAS) Sediment Trap (RESCON-2) Sediment Trap (HEC-RAS) Sluicing (RESCON-2) Flushing (RESCON-2) Dredging (RESCON-2) Sluicing + Sediment Trap (RESCON-2) 0% 25% 50% 75% 100% 0 0.5 1 1.5 2 0 10 20 30 40 50 60 70 80 90 100 Years of Operation 649