Bhutan's quest for energy security and development.

The rush of water ripped through the valley like an excavator. On August 6, 2019, unusually heavy monsoon rain drenched the mountainside above the Punatsangchhu river in Bhutan, causing an artificial lake to form from the debris buildup. The debris dam burst from the pressure, sending water gushing down the steep hillside.

Boulders the size of buses from the cliffs above lay exposed in the flood zone. All that remained of a concrete bridge were the pillars on either end. Whole trees lay upended in the mud like toothpicks. Downstream, where this usually small river joins the much bigger Punatsangchhu, it was chaos. A block in the river flooded the main highway.

Standing trees had water up to their crowns. The redirected river swamped an equipment storehouse belonging to the Indian company Bharat Heavy Electricals Limited, one of the contractors of the struggling Punatsangchhu-II hydropower project. About 110,000 USD worth of equipment was ruined or washed away towards the Indian border.

As the...