Page - 952 - in Book of Full Papers - Symposium Hydro Engineering

Fig. 1 Upstream vertical unfold view of Xiaowan arch dam HYDRAULIC PROBLEMS AND DOWNSTREAM AREAS PROTECTION The elevation of emptying facilities is much lower than any other discharge facilities. So the hydraulic problems such as high water level, high speed flow and cavitation when reservoir emptying, especially emergency emptying, along with energy dissipation and erosion control problems as well as investment should all be took into account. On the other hand, man-made extraordinary flood should not occurred in the downstream areas even if emergency emptying. SUBJECTS NEED TO BE FURTHER RESEARCHED ABOUT EMPTYING DESIGN OF HIGH DAMS The emptying requirements and process are much complex and some factors should be considered in the emptying design, including the relationships and requirements of integral safety degree and the water level for overhaul, hydrologic characteristics and downstream area flood control, arrangement conditions and sizes of emptying facilities as well as reservoirs slope stabilities when emptying. Through comprehensive and thematic analysis, a proper emptying ending water level and emptying facilities scale should be chosen to satisfy the dam overhaul requirements, ensure dam safety risk acceptable and prevent dam failures or other secondary disasters. DAM INTEGRAL SAFETY DEGREE The water thrust acted on concrete dams can be reduced by lower down the reservoir water level, which is very effective to increase the stabilities of dam foundation and dam abutment. In case of emergency, the first consideration is to enhance the dam integral safety degree as soon as possible, though that may cause excess concrete tensile stress at some local areas. 952