Optimisation of Hydraulic Design of Uri-II Dam Spillway, Jammu and Kashmir

Abstract

Optimisation of hydraulic design of spillway involves verification of designs of various components of spillway which includes crest profile of spillway and bottom profile of breast wall, adequacy of spillway spans to pass the design flood, the sufficiency of divide walls and training walls, location of trunnion of gates, assessing the performance of energy dissipator, assessing the scour downstream of ski-jump bucket, design of pre-formed plunge pool, location of head regulator/power intake structure and upstream and downstream protection subjected to design floodwaters. Hydraulic model studies play a key role in optimising the designs of various components of the spillway as mentioned above. Hydraulic design of spillway of Uri-II dam was optimised in CWPRS, Pune, by conducting hydraulic model studies. Uri-II H.E.Project was envisaged as a run-of-the-river scheme on the River Jhelum in Uri Tehsil of Baramulla District of Jammu and Kashmir. It has a power generation capacity of 240 MW (4 units of 60 MW each) utilising a gross head of about 130 m. The project consists of a 52 m high and 173 m long concrete gravity dam with a 4.27 km long headrace tunnel (8.4 m diameter), a restricted orifice-type surge shaft (25 m diameter), two 5 m diameter steel-lined penstocks, four 3.5 m diameter bifurcated steel-lined penstocks, an underground powerhouse and a horseshoe shaped tailrace tunnel 3.77 km in length. The spillway is designed to pass design outflow flood of 4850 m³/s at FRL El. 1241 m and also to flush the sediment deposited in the reservoir into the river downstream. A breast wall spillway has been proposed with four low-level orifices of size 9 m wide × 11.4 m high (originally 12 m high) with crest level at El. 1217 m. The ski-jump bucket is provided for energy dissipation with invert at El. 1210.19 m and lip at El. 1213 m. The project was completed and all four units were commissioned and the 4th unit in July 2014. Hydraulic model studies enabled optimisation of various components of spillway by optimising the size of spillway spans and design of natural plunge pool and suggesting downstream hill slopes protection. Optimised hydraulic design was made by assessing the discharging capacity of the spillway, validating crest profile with pressures on the spillway surface, the performance of energy dissipation arrangement for the entire range of discharges, flow conditions in the reservoir upstream of the spillway and head regulator, flow conditions downstream of the spillway and head regulator and requirement of a natural plunge pool with expected scour levels. This paper provides detailed information on the hydraulic model studies carried out on the spillway and energy dissipator of Uri-II dam spillway, Jammu and Kashmir.