Experimental Investigation On The Hydraulics Of Stepped Spillways

Stepped spillway is one of the new kinds of the spillways with high rate of energy loss, which is based on RCC technique . Stepped spillways have become the preferred spillways in medium-size and small-size projects in recent years due to its special shape and remarkable rate of energy loss, which also have been introduced in the high water level water works. However, the research on hydraulics of stepped spillways is just on the start point and the materials of stepped spillways is insufficient. By the method of model tests and theoretical analysis, flow form, pressure characteristic, water-surface curve, velocity , air entrainment and energy dissipation have been studied in this paper. These efforts have great significance in the development and applications of the Stepped spillways.Conclusions can be drown as follows through model test:1. There are two flow forms in the stepped spillways , which are skimming flow and jet flow. Jet flow occurs when the runoff is small and the critical water deep is lower than the height of the step's, otherwise skimming flow occurs.2. The time-average and pulsant pressure characteristic have been studied. The time-average pressure in the step' surface falls down and then increases from the nook to the salient. The minimum point is in the distance of 0.3-0.4 time pace from the nook while the maximum point 0.7-0.9 time pace and the pressure falls down to some extant in the salient when the grade is small. The minimum point is in the distance of 0.5 time pace from the nook while the maximum point is around the salient when the grade is big. The time-average pressure on the vertical section reaches the maximum point in the nook , the negative point in the half step and the maximum negative point in the edge of the salient The along-road distributing of the time-average pressure is wavy that is the minimum point and the maximum point occurs alternately in the steps.The pulsant pressure increases from the nook to the salient in the steps and the along-road distributing of the pulsant pressure is also wavy.3. The method of the calculation of the water-surface curve has been given in the paper and also the law and the equation of the diversification of the velocity index have been . studied. The calculating method of the along-road loss of the water level has been given.4. The division method of the air entrainment has been announced that is bottom air entrainmentzone> cuniform pure water zone - bubble zone and drip zone. The calculating method of initial entrainment point in the stepped spillway has been announced. The average air entrainment thickness and water containing index have been calculated. The distribution of the sectinal air entrainment thickness and the along-road air entrainment thickness have been investigated.5. The law of the energy dissipation rate's along-road diversification has been studied and the calculation method of the energy dissipation rate under dams has been declared.