Model Test On Drop Slit-Bucket Of The Middle Outlet Works In Arch Dam For Dahuashui Hydropower Station

In water conservancy and hydropower project, outlet works are a key for the safety of reservoirs. Energy dissipation problem has been always encouraged to research.Because arch dam is thin relatively,use slit-bucket on the middle outlet works, slit-bucket and the work gate of outlet all on the cantilever. The bucket should be short enough, water surface low enough. So the conventional slit-bucket does not meet the requirements. Drop slit-bucket is a special kind of slit-bucket, it is short, and has a lower pick up water level, can adapt to a large range of water head.This paper aims at middle outlet works in arch dam for Dahuashui Hydropower Station, through model tests, get a type of drop slit-bucket that fit the project. Then compare with typical flatbed slit-bucket, and summarize their hydraulic characteristics.Through the tests, the author makes out the following conclusions:(1) On flatbed slit-bucket, when the contraction cone is short, the water fluent impact support beam of working arc gate, while on drop slit-bucket, it can reduce the water surface effectively, water fluent does not impact the support beam of arc gate, there is integrity cavity at the subduction of the chute bottom, floor plate without water force.(2) When the water level is low, the water flow can not form a nappe of proliferation, while on drop slit-bucket, the water flow can form the diffused nappe at orifice flow.(3) The horizontal length of upper and lower edge of water nappe in drop slit-bucket are all shorter than flatbed slit-bucket, but the length of water nappe grow 20%~50%, energy spread, it is good for scour protection.(4) Compare to flatbed slit-bucket, water pressure on floor plate and side wall of drop slit-bucket reduce about 20%, it is good for safety of the middle outlets.(5) Dissipation effect of drop slit-bucket is better than its on flatbed slit-bucket, depth of scouring decrease about 20%.This test solved hydraulics problem in middle outlet of Dahuashui Hydropower Station. The result has been used by the project.