Hydropower is one of the oldest forms of energy production. It is also a renewable resource. It is renewable because we can use it to create electricity from a renewable energy source – falling or moving water.
The fall and flow of water is part of a continuous natural cycle. During this hydrologic cycle, water evaporates from lakes and oceans. It forms clouds in the atmosphere and then falls back to the earth in the form of rain or snow. The rain and snow replenish our rivers and streams.
Each winter, falling snow accumulates in the mountains. In the spring, the force of gravity moves the melted snow from higher to lower elevations, increasing river flows. Winding and weaving a path to the ocean, some of these river flows are used to create hydroelectric power. After passing through a turbine at a dam, the water is returned to the river, unchanged and unpolluted, to continue its journey to the ocean.
The hydrologic cycle places hydropower at the mercy of Mother Nature. This is why many hydro projects store water in their reservoirs (behind dams) for future power generation. This stored water also aids in flood control and can be used for irrigation and recreation.
As long as the hydrologic cycle repeats itself, with falling rain and snow, we won’t run out of the fuel it takes to make hydroelectricity.