At Tehri Project, the spillways have been designed for a Probable Maximum Flood (PMF) of 15540 cumecs computed for a return frequency of 1 in 10,000 years. The routed flow through the designed structures is 13040 cumecs at the maximum level of the reservoir. Tehri spillway structures consist of a number of unique features, which are being implemented in India for the first time. The spillway system comprises of a chute spillway with three bays along with four shaft spillways designed for a head of 220 m. The shaft spillways utilize the existing four diversion tunnels which would have otherwise become redundant after plugging of the tunnels at the end of construction period. The experience during the construction of these shaft spillways has been methodologically and technologically unique as the design measures adopted during the execution proved to be successful in completing the activities. The paper outlines few such experiences along with the design measures applied.
