Study On Two-stage Ski-jump Energy Dissipation For High Dam

With the rapid development of economic construction and water conservancy in our country, a batch of giant projects with high head has been or will be built. Most dams of these projects are above the height of 200 meters. However, the construction of high dam features large discharge, high head, complex geological condition, large flood power, narrow river valley, and so on, which lead to the severe flood discharge and energy dissipation problem. Closely combined with actual project, this paper propose the two-stage ski-jump energy dissipation scheme for high dam, on the basis of large scale hydraulic model test of the tunnel spillway of Houzhiyan hydropower station. The test and hydraulic calculation indicates that this novel energy dissipation proposal can effectively lighten the downstream river bed scour and atomization phenomenon, and further ensure the project's security and rationality. The main research contents in this paper are as follows.(1) This paper introduces related concepts and significance of flood discharge and energy dissipation, and also elaborates its usual patterns as well as the selecting methods or principles. In addition, the current situation of efficient energy dissipator is discussed as well in this paper.(2) This paper introduces the fundamental principles and problems concerning ski-jump energy dissipation, such as the caused high velocity flow issues, the types and parameters of trajectory bucket, the design of downstream plunge pool, the calculation of jet trajectory length, the estimation of scour hole depth. The research approachs and development trends of ski-jump energy dissipator is also discussed in this paper.(3) Closely combined with large-scale hydraulic model test of the tunnel spillway of Houzhiyan hydropower station, This paper analyzes the hydraulic characteristics and energy dissipation problems for spillway's original scheme.(4) According to the project's practical situation, this paper presents the optimum proposal of tunnel spillway and studies its hydraulic characteristics. What calls for special attention is that the optimum proposal innovatively adopts terrace-based two-stage ski-jump energy dissipator, making use of the outlet's actual landform.(5) This paper analyzes the stability of outlet's concrete terrace in the optimum proposal, which further proves the rationality of two-stage ski-jump energy scheme. This paper also discusses the way to estimate jet trajectory length and scour hole depth of two-stage ski-jump, through using that of common ski-jump.