Page - 1535 - in Book of Full Papers - Symposium Hydro Engineering

2. Main components of a water conveyance system for diversion of river water consist of the following components: 1. Intake structure 2. Water conducting system (Tunnel) comprising of control structures. 3. Outflow structure, which joins river flow downstream 2.1. INTAKE STRUCTURE ENTRANCE An intake is provided at the mouth of a water conveyance system for a diversion of river flow. It is designed with the following points: 1. There should be smooth entry of water in to the tunnel as water enters from the reservoir behind a dam or the pool behind a barrage into the tunnel. 2. There should not be any formation of vortices that could draw air into the water conducting system. 3. There should be minimum entry of sediment into the water conducting system. 4. Floating material should not enter the water conducting system. Inlet structure: Inlet transition facilitates the flow acceleration, ensuring the transition from subcritical flow which is established upstream in the reservoir created by the construction of the cofferdam or, in some cases, the channel connecting the bed to the frame, to supercritical flow that occurs in the diversion tunnel. The implementation of this structure aims to promote sufficient air to the flow, so that it develops a pressure equal to atmospheric pressure along the tunnel. This avoids the possibility of reaching pressures near the water vapour pressure, reducing the risk of cavitations phenomena in the diversion tunnel and hence its erosion. Regarding installation of the inlet structure it may be implemented directly on the ground or resort to auxiliary concrete that supports it above the ground level. For smooth entry of water in to the tunnel, generally following elliptical equation is used (1) 1 33.0 2 2 2 2   D y D x 1535