Hydraulic Assessment of Multiutility Tunnel.

Present day trend is to make optimum utilization of water conductor system. Use of tunnel for various purposes like diversion during construction and depletion of reservoir after construction is over, as an access, a surge gallery, ventilation, and as adit etc. A river diversion tunnel is used to divert river water during construction of a project. Once construction is over, diversion tunnel is plugged before initiating storage of water consequently this tunnel part becomes redundant. Tunnel construction has high costs and usually adopted when other solutions are unfeasible. Concept of multi utility tunnel-diversion, depletion as well as access economically helps in reduction of project cost. Making use of redundant part of diversion tunnel, at later stage employed for permanent use of depletion of reservoir. No universally accepted standards are available for design of temporary structures like diversion tunnels.. To minimize the project cost, part of diversion tunnel can be reused for depletion of storage. There are instances where part of river diversion tunnels have been used as depletion tunnel after construction of dam is completed. In India projects such as Yamuna, Doyang, Nagarjunsagar, Salal have successfully used the concept of multipurpose tunnel for diversion of river flow and depletion of reservoir. Hydraulic design associated with such tunnels has to function satisfactorily for high discharge at low head during construction and high head low discharge during operation period of project.This paper describes various hydraulic aspects related to diversion cum depletion tunnel carried out at CWPRS,Pune. Major problems in design of multi utility tunnel- used for diversion of river flow as well as depletion of reservoir for water flow are flow conditions in approach to tunnel, in tunnel and downstream of tunnel. Major head loss in tunnel flow is due to friction. Detailed information on investigation by various researchers related to friction factor is tabulated a Increasing urban population coupled with pace of industrial and other developments led to increase in water demand and stress of infrastructure for water supply . Many metropolitan and urban cities are facing acute shortage of water for domestic and industrial purposes To reduce the stress on water supply infrastructure, existing water sources are utilized to fullest and new sources are continuously added to augment the water supply. Even though art of tunneling is very old and well documented, new challenges in economical design and construction in difficult situations are added over the years. In this paper various formulae proposed by investigators are presented in annexure for ready reference