Hydrology, << hy DROL uh jee, >> is the study of the movement and distribution of the waters of the earth. People use billions of gallons of fresh water every day. Hydrologists (scientists who study water) help provide information needed to find adequate supplies of fresh water. They also study floods and water pollution. In addition, hydrologists study the chemical and physical properties of water.
In nature, water circulates through a system called the water cycle or hydrologic cycle. This cycle begins when heat from the sun causes ocean water to evaporate and become water vapor. The atmosphere holds the water vapor while the vapor gradually cools and forms clouds. The water eventually falls as rain or snow. Most rain and snow falls back into the oceans. But some falls on the land and flows back to the seas, completing the cycle. See Water (Nature’s water cycle) .
There are two main sources of fresh water: (1) surface water and (2) ground water. Surface water flows over the land in lakes, rivers, and streams. Ground water seeps through the soil or through tiny cracks in rock. Some ground water flows in underground rivers.
Hydrologists study the water cycle to locate sources of fresh water. They help choose the best sites to drill wells to find ground water in desert areas. Hydrologists also help plan dams and irrigation projects.
Hydrologists try to prevent or reduce water pollution. They study the effects of pollution as it moves through the water cycle.
Hydrology provides information that scientists need to predict and control floods. Architects and civil engineers use this information to help plan towns and roads safely near waterways where floods often occur.
See also Water cycle .
