5.4 Water Release Structure
5.4.1 The types，dimensions and elevations of water release structures of a hydropower station shall be determined after techno-economic comparison according to topographical and geological conditions，layout of the project，sedimentation，release volume，construction quantity，construction and investment，etc.
5.4.2 The setup of release sluice of a hydropower station shall be determined according to the requirements for water supply，environmental protection，sediment discharge，and overhaul，etc.
5.4.3 For earth-rock fill dams，open spillway should be used as the water release structure；if limited by conditions，open-intake free-flow tunnels may be adopted.The connection between the spillway and the earth-rock dam shall be designed to meet the requirements for strength，stability against sliding and stable seepage.
5.4.4 For concrete dams and stone masonry dams，crest overflowing should be adopted，and water release through the dam orifice or discharge tunnel may be adopted as well.
5.4.5 For hydropower stations in river channel，gates and dams should be used for flood discharge.
5.4.6 The safety of water retaining structures and other major structures shall be guaranteed and the requirements for flood control by downstream river course shall be met when discharging the design flood；the safety of water retaining structures shall be guaranteed when discharging the check flood.
5.4.7 Energy dissipation and protection facilities shall be installed downstream of the flood discharge structures.The method of energy dissipation shall be identified after techno-economic comparison of upstream and downstream water levels，discharge volume，topographical and geological conditions，and operating mode，etc.
5.4.8 For water release structures，hydraulic calculation shall be made on discharge capacity，water surface profile，aeration of high-velocity water flow，anti-cavitation，energy dissipation and anti-scouring etc.For water release structures with large release volume and complicated flow patterns，a hydraulic model test should be performed.
5.4.9 Open spillway shall be located on a stable foundation，while its axis should be a straight line，the flow at intake and outlet should be smooth and the connection to the water surface should be smooth and steady，and the discharge flow shall be kept at a safe distance from the dam body and other structures.
5.4.10 The selection of pressure flow or free flow in a discharge tunnel shall be subject to the technoeconomic comparison.For a water release tunnel with high-velocity flow，the flow shall not alternate between pressure flow and free flow in the same section.
5.4.11 After techno-economic comparison，the construction diversion tunnel may be used as discharge tunnel and bottom outlets.(https://www.daowen.com)
5.4.12 The elevation of the flood gate sill shall be determined after techno-economic comparison according to conditions of flood regulation，flood and sediment discharge，type of weirs and gates，construction diversion，and topography and evolution trend of the riverbed.The elevation of sill should not be lower than that of riverbed.
5.4.13 The flood gate on a soft foundation shall be installed as an integral structure with a symmetric layout.If the base slab of the gate chamber is located on a medium compacted foundation or in regions with seismic intensity of 7 degree or above，an integral flat base slab should be used；if it is on a compacted foundation，the separation flat base slab，box flat base slab，fold line base slab or inverted arch base slab may be used；if the foundation surface is soft，a low weir base slab may be used.
5.4.14 For flood gate installed on a rock foundation，the separation flat base slab may be used for the gate chamber，and an integral flat base slab should be used in regions with seismic intensity of 7 degree or above.
5.4.15 For flood gate installed on a soft foundation，a blanket shall be arranged upstream of the gate chamber.For downstream energy dissipation，the hydraulic jump method should be applied，with apron，riprap and anti-scour wall or channel installed as required.
For gates installed on sediment-laden rivers with many large gravels，plunge pool should not be installed downstream；but the method of using inclined apron to divert rapid stream may be adopted for energy dissipation，by which an anti-scour and abrasion resistant inclined apron is built to connect with the downstream river reach，and its end shall be installed with an anti-scour wall or channel.
For flood gate installed on a river reach in mountainous region，its downstream apron and riprap should be constructed with materials of good integrity.
5.4.16 For different types of water release structures，the following structural and stability computations shall be conducted respectively:
1 Stability，foundation stress and structural strength of open spillways and flood gate chambers.
2 Stability and structural strength of steep channel of spillways and energy dissipation facilities.
3 Structural strength of lining of discharge tunnels.
4 Permeable stability of flood gate and settlement of soft foundation.
