Page - 335 - in Book of Full Papers - Symposium Hydro Engineering

3. ANALYSIS OF SEDIMENTATION IN THE MANWAN RESERVOIR 3.1. THE SEDIMENTATION FORM OF THE RESERVOIR The sedimentation analysis shall be based on the section drawings based on the data collected during the surveys in 2005, 2009 and 2014, as shown below: (1) Fig. 2 is the Main-Stream Talweg Longitudinal Section of the Reservoir, which shows that the sedimentation takes on an obvious delta deposit form, with a front slope gradient of about 2.6‰ and a top slope gradient of about 0.20‰. The sedimentation surface of the delta has been raised year by year and pushed forward to the dam. The head of the delta is about 16.9km from the dam, and the top elevation of the delta is about 983.34m, trending basically the same as in 2009. The reservoir has not reached the balance between scouring and silting. (2) The Xiaowan HPP was impounded in 2009, thus, based on the relevant data, the yearly average sediment volume to be retained of the Xiaowan Reservoir is 48 million tons (about 32million m3) above the dam site, which greatly relieved the sediment problem of the Manwan HPP. In terms of the lateral distribution of sedimentation of the reservoir, compared with the results in 2009, the sedimentation volume for the whole reservoir is relatively small, the sedimentation volume in the section in front of dam (dam - LM35 section) is more than the back section, with the average sedimentation height of 1.2m and the highest sedimentation height of 6.1m; The sedimentation volume in the section in the middle of the reservoir (LM36 - LM55) is relatively small with the average sedimentation height of 0.5m; The section at the end of the reservoir (LM56 - LM73) generally shows the scouring, which mainly occurred on both sides of the reservoir; For the section conditions, the section in front of the dam (LM09 - LM35) basically shows the horizontal sedimentation, and the section in the middle of the reservoir mainly shows the balance between scouring and silting, the sedimentation volume in the section at the end of reservoir is quite small, and the section near the Xiaowan dam site shows the scouring on both sides. (3) There are few tributaries in the Manwan Reservoir area, and there is only one bigger tributary – the Gonglang River in the reservoir area. The distance from the mouth of the tributary to the Manwan dam site is about 21km. The upstream area basically shows the scouring, while the scouring volume is quite small. And, as per the scouring sedimentation volume, the Gonglang River has basically reached the balance between the scouring and silting. 335