Today, there are approximately 850,000 dams located around the world. Of the more than 40,000 that are categorized as large dams, more than half are located in China and India.

Where should a dam be built?

Dam construction must be started when river levels are low. A small dam called a cofferdam is built upstream of the construction zone to help funnel water into the diversion tunnel. A cofferdam may be built downstream as well, but the overall goal is to keep the construction zone dry so that the main dam can be built.

Why are dams built?

A dam is a structure built across a stream or river to hold water back. Dams can be used to store water, control flooding, and generate electricity.