Page - 951 - in Book of Full Papers - Symposium Hydro Engineering

ENHANCE EMPTYING ABILITY Due to technology limitations of sluices and hoists, the intake elevation of emptying facilities cannot be set too low. The water head before the sluice of emptying facilities should not be greater than 120m usually, maximum 160m; otherwise the sluice will bear too large thrust. The water head and capacity been emptied are both limited. So it is very necessary to research the feasibility and rationality of lowering the intake elevation of emptying facilities. SHORTEN THE EMPTYING TIME Because of restriction by water thrust on sluice gate, the size of emptying tunnel cannot be designed too large and the discharge flow of it is limited. So the emptying time is too long sometimes to ensure the safety of projects. Such as Lianghekou project, the sluice gate size of emptying tunnel is 8m by 10m, while the water head before the gate reaches 125m, which need 87 days to discharge to designed emptying water level in dry season. So it is necessary to consider hydrologic conditions of both flood season and dry season as well as project investment to research the arrangement and structures of emptying facilities and then shorten the emptying time. The emptying facilities in China are designed considering the requirements of emptying for overhaul under exceptional circumstances in dry season. ROUTINE MAINTENANCE OF EMPTYING FACILITIES Usually, the emptying facilities cannot be used until the reservoir water level falls to a very low level. Most of them are rarely used and have very few chances to operate and be maintained. So it should be pay attention to how to make sure the emptying facilities can operate normally at key time. In addition, the intake of emptying facilities should not be set too low because of sediment deposition. The intake elevation of bottom emptying outlets of Xiaowan arch dam (Fig. 1) is 1080m, which can be partly or must be totally opened when the reservoir water level is lower than 1160m or between 1160m and 1186m, respectively, and cannot be used when the water level is higher than 1186m. Nevertheless, as a multi-year regulating reservoir, the designed dead water level and flood season limited water level are 1166m and 1236m, respectively, much higher than 1186m. So it is obviously that the bottom emptying outlets have almost no chance to operate and be inspected. 951