To build India's Polavaram dam, engineers moved the Godavari River sideways
The riverbed at Polavaram in Andhra Pradesh is deep sand, too soft to hold a spillway. So engineers shifted the whole Godavari about 6.6 km towards its right bank and built there instead. The resulting spillway, with 48 giant radial gates, is described as the world's largest by discharge capacity.
The idea is old. In July 1941 the Madras Presidency first floated a reservoir at the site, and its chief irrigation engineer, L. Venkatakrishna Iyer, surveyed it and proposed watering 350,000 acres across two growing seasons plus a small 40 MW power plant. A foundation stone was laid in 1980, but for decades the dam stalled on cost: at Polavaram the river spreads roughly 1.5 km wide over bedrock buried more than 30 m down. A narrower gorge upstream in the Papi hills was considered and rejected, and when work finally began in 2004 the old design was reused.
The finished scheme is enormous. An earth-and-rock-fill dam about 2.5 km long crosses the river, sealed underneath by a concrete diaphragm wall reaching up to 95 metres into the riverbed to stop water seeping through the sandy foundation, the first such wall in India. Three natural hillocks act as anchors. The spillway, a little over 1.1 km long, is designed to pass an extreme flood of about 141,000 cubic metres per second. There is even a fish ladder built into the dam complex, the first of its kind in the country.
Its reservoir backs up about 150 km along the Godavari and reaches into Chhattisgarh and Odisha, and is meant to irrigate some 2.32 million acres and feed a 960 MW power station with 12 turbines. Two canals, each over 170 km long, carry water away, one linking to the Krishna River.
Construction has broken records and budgets alike. On 7 January 2019 contractors poured 32,100 cubic metres of concrete in 24 hours, beating a Dubai record and earning a Guinness entry. The price has climbed too, from 129 crore rupees when the project was conceived in the 1940s to a reported 58,319 crore in 2018.
Source: Polavaram Project
