High impact: India's $3.5BN new mega-dam changes the weather

India is building a massive new megaproject — a multi-purpose irrigation system that's been almost a century in the making. Called the Polavaram Project, it's become known as the 'lifeline of Andhra Pradesh' — a state that experiences both devastating floods and searing droughts.

Consisting of the largest spillway in the world, a 2.5km earth and rock dam, a pair of huge canals and a hydro plant it promises to control water levels across a region prone to natural disasters. But can this scheme that's already been dragging on for decades finally get over the finish line?