Science Explorer. Multimedia Gallery. Park Passes. Technical Announcements. Employees in the News. Emergency Management. Survey Manual. When looking at the location of rivers and the amount of streamflow in rivers, the key concept is the river's "watershed". What is a watershed? Easy, if you are standing on ground right now, just look down. You're standing, and everyone is standing, in a watershed. A watershed is an area of land that drains all the streams and rainfall to a common outlet such as the outflow of a reservoir , mouth of a bay, or any point along a stream channel.
Watersheds can be as small as a footprint or large enough to encompass all the land that drains water into rivers that drain into Chesapeake Bay, where it enters the Atlantic Ocean. This map shows one set of watershed boundaries in the continental United States; these are known as National hydrologic units watersheds. The word "watershed" is sometimes used interchangeably with drainage basin or catchment.
Ridges and hills that separate two watersheds are called the drainage divide. The watershed consists of surface water --lakes, streams, reservoirs, and wetlands --and all the underlying groundwater.
Larger watersheds contain many smaller watersheds. It all depends on the outflow point; all of the land that drains water to the outflow point is the watershed for that outflow location.
Watersheds are important because the streamflow and the water quality of a river are affected by things, human-induced or not, happening in the land area "above" the river-outflow point. This picture gives a good representation of a watershed. It only shows a part of the Agashoshok watershed, but you can see how precipitation that falls on the near side of the ridges will move down-gradient to flow into the river in the picture.
It is sometimes called a drainage basin. Students learn the components of a watershed, identify examples of point and nonpoint source pollution, and then build a 3-D watershed model.
Students learn how watersheds work and why they are important, before locating their local watershed online. Finally, students complete a Project Journal at the close of the activity to reflect on their learning. Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. Image The Rivers of the Mississippi Watershed The Mississippi and Missouri Rivers are the two longest rivers in North America, and together form the backbone of the much larger Mississippi watershed that supplies freshwater to a huge portion of the continental United States.
Photograph by Horace Mitchell. Twitter Facebook Pinterest Google Classroom. Encyclopedic Entry Vocabulary. Media Credits The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.
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Watershed Basics. What is a Watershed? Rivers and streams nourish and connect ecosystems throughout the watershed. Wetlands and lakes help to store and filter water, and provide habitat for fish and wildlife. Upland forests and meadows provide habitat for wildlife and nutrients for aquatic ecosystems, and encourage infiltration of rainwater into the ground. Watershed sources, such as reservoirs and groundwater, supply us with clean water for drinking and irrigation. The various components of watersheds provide opportunities for recreation, tourism, education and aesthetic appreciation.
Our Impact on Watersheds Over the years we have changed many of our natural watersheds into urban watersheds. Heavy rains caused landslides in the hills. Many homes and entire villages were washed away. Many people died and many more became ill. The villagers began to understand that to improve their health, they had to protect their watershed. After the discussion of the "Health effects of damaged watersheds," the Aguan River Valley story continues When land is cleared of trees and plants deforestation , soil holds less water, drying up wells and springs.
Dry periods may become longer or more frequent, causing all the health problems of not having enough water. Deforestation also causes loss of soil erosion which makes growing food more difficult, leading to hunger and migration.
When wetlands are destroyed, they cannot filter toxic pollution out of the water, leading to greater contamination. Damage to wetlands and deforestation both cause flooding, which leads to injury, death, and increases in diarrhea diseases.
Mosquitoes breed in slow-moving and standing water. When large or sudden changes are made in how land is used and how water flows through the watershed, they often create conditions for mosquitoes to breed.
Changes from:. If you can keep the water moving, changes to the watershed do not have to lead to more mosquito-borne illnesses such as dengue, malaria, and yellow fever. For more about preventing problems from mosquitoes, see Chapter 8. Healthwiki Buy books Donate About us Hesperian. Hesperian Health Guides. Books and Resources.
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