Underground hydroelectric power stations

THE NATURAL waterfalls in Sweden are often very extended in length. The utilized head in the power stations is frequently less than 150 feet and only in rare cases exceeds 300 feet. The mean flow of water in the bigger rivers amounts to about 10,000 cubic feet per second at the mouth. Kaplan turbines have been used for heads up to 110 feet; for greater heads, Francis turbines are used.