Water energy

Hydropower Relies on the Water Cycle
Understanding the water cycle is important to understanding hydropower. In the water cycle:
Solar energy heats water on the surface, causing it to evaporate.This water vapor condenses into clouds and falls back onto the surface as precipitation (rain, snow, etc.).
The water flows through rivers back into the oceans, where it can evaporate and begin thecycle over again.

Hydropower & the Environment

Most dams in the United States were built mainly for flood control and supply of water for cities and irrigation. A small number of dams were builtspecifically for hydropower generation. While hydropower (hydro-electric) generators do not directly produce emissions of air pollutants, hydropower dams, reservoirs, and the operation of generatorscan have environmental impacts.

A dam to create a reservoir may obstruct migration of fish to their upstream spawning areas. A reservoir and operation of the dam can also change the natural watertemperatures, chemistry, flow characteristics, and silt loads, all of which can lead to significant changes in the ecology (living organisms and the environment) and rocks and land forms of the riverupstream and downstream. These changes may have negative impacts on native plants and animals in and next to the river, and in the deltas that form where rivers empty into the ocean. Reservoirs may coverimportant natural areas, agricultural land, and archeological sites, and cause the relocation of people.

Tidal Power
Tides are caused by the gravitational pull of the moon and sun, and therotation of the Earth. Near shore, water levels can vary up to 40 feet due to tides.
A potential disadvantage of tidal power is the effect a tidal station can have on plants and animals in the estuaries.Tidal barrages can change the tidal level in the basin and increase turbidity (the amount of matter in suspension in the water). They can also affect navigation and recreation.

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