Seite - 1534 - in Book of Full Papers - Symposium Hydro Engineering

Figure 3: Tunnel for inter linking Beas and Satluj rivers In addition to transferring water from deficit region, diversion tunnels are used to divert water during construction of dam. The scheme of this type of diversion is characterized by the completion of the diversion tunnel and two coffer dams (upstream and downstream) that will dry the area, in which, it is intend to carry out the dam construction. Tunnels are commonly used to convey water from its source to demand area. Even though costly, compared to surface hydraulic structures, depending upon geological features of the surrounding hills. Complicated geological conditions and extraordinary geological occurrences such as intra- thrust zones, very wide shear zones, geothermal zones of high temperature, cold/hot water springs, water charged rock masses, intrusions, fault planes, etc. should preferably be avoided. Sound, homogeneous isotropic and solid rock formations are the most suitable for tunnelling work. However, in the Himalayan region, such conditions are rather rare compared to the hills of peninsular India. This is because the Himalayan geological formations are mostly sedimentary in nature whereas the peninsular upland of the country is of igneous nature. Hence, geological investigations have to be carried out in detail before a tunnel alignment is finalized. The river diversion tunnel has the function to drain the bypass flow, and may have several sections. However, the sections most frequently used are circular and horseshoe. The choice and design of the type of section employed is related to the final design of the diversion tunnel in relation to its integration or not in the definitive structure. The diversion of the river through tunnels can be held in free surface or pressure flow. 1534