Seite - 539 - in Book of Full Papers - Symposium Hydro Engineering

Fig 5. Layout of the Weir Site(Detail design, 2015) 3.3. NUMERICAL ANALYSIS 3.3.1. Input data and boundary conditions A numerical analysis was carried out to verify sedimentation management performance of the OHDS technique(HR Wallingford, 2014). The long series of water discharges, from 1960 to 2007 has been used in this analysis as input data. The sediment rating curve described in the Feasibility Study was used to define the amount of suspended material. As well, a bypass tunnel and MP were considered. The diameter, length and discharge capacity of the bypass tunnel were 8.5m, 229m, 804m3/s respectively. The water discharge is split according to the following rule: when discharge is less than 200 ㎥/s, the bypass tunnel is closed and all water and sediment passes over the coffer dam. When discharge is more than 200㎥/s, the bypass tunnel is opened and the discharge in excess of 153㎥/s, the design discharge rate, flows through the bypass tunnel. 3.3.2. Analysis results First, we analyzed the effects of reducing sedimentation using the bypass tunnel. The results show that any coarse material, gravel fractions > 2.9㎜, will bypass through the tunnel. 47% of the sand material transported by the flow (as average), with diameters from 0.1 to 0.92㎜, will be conveyed towards the MP. The results show that the amount of sand that flows over the cofferdam towards the MP has been fairly constant for all the years (around 0.56Mt) 539