Problems in the water of the Durolle became more frequent in the early 20th century. To begin with, the flow of the river in summer is low and very irregular, resulting in a commiserate level of unemployment. In effect, the water-powered mills are unable to operate without enough water flow. In winter, the opposite occurs, and the Durolle becomes a torrential flood with considerable force. The town of Thiers is one of the most vulnerable to floods in Puy-de-Dome, and the Vallée des Rouets is the area of the town most affected.