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watershed

watershed, elevation or divide separating the catchment area, or drainage basin, of one river system or group of river systems from another system or group of systems. The term is also often used synonymously with drainage basin. The continental divide in the US along the Rocky Mts. forms the watershed division between westward-flowing and eastward-flowing streams; the Mississippi watershed extends from the Rockies to the Appalachians. Often the watershed is a range of mountains, the two sides of which have widely different climatic characteristics, as in the Americas and Australia. The low Valdai Hills are an important watershed of Russia.

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watershed

wa·ter·shed / ˈwôtərˌshed; ˈwä-/ • n. an area or ridge of land that separates waters flowing to different rivers, basins, or seas. ∎  an area or region drained by a river, river system, or other body of water. ∎  an event or period marking a turning point in a course of action or state of affairs: these works mark a watershed in the history of music.

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watershed

watershed
1. See DIVIDE.

2. See CATCHMENT.

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"watershed." A Dictionary of Earth Sciences. . Encyclopedia.com. 26 Sep. 2018 <http://www.encyclopedia.com>.

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watershed

watershed
1. See divide.

2. See catchment.

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"watershed." A Dictionary of Ecology. . Encyclopedia.com. 26 Sep. 2018 <http://www.encyclopedia.com>.

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watershed

watershed •flatbread • bedspread • teabread •sweetbread • retread • crispbread •wingspread • widespread • cornbread •shortbread • sowbread • proofread •pure-bred • gingerbread •thoroughbred • aforesaid • Holinshed •cowshed • woodshed • woolshed •bloodshed • watershed • Stansted •farmstead • bedstead • Hemel Hempstead • roadstead • homestead •newly-wed

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Watershed

Watershed

Resources

A watershed refers to land that is drained by an interconnected system of rivulets, streams, rivers, lakes, and groundwater to a particular point. Both rain and snow contribute to the watershed. The topography of a region sets the boundaries for a watershed, which are defined by the highest regions around a stream. Any drop of water falling on land within the water shed will drain into the watershed. Any drop falling on land outside highest points of the watershed will drain downward into another watershed. Watersheds can range in size from just a few square miles to many hundreds of square miles. The related terms catchment and drainage basin refer to the total area of land that drains into a water body.

Watersheds are important for many reasons. They are a direct link to the water quality of a region. They impact the amount and intensity of flooding. Fisheries yields are related to watershed health. Watersheds are key natural areas that serve as habitats for many plants and animals as well as for human recreational use.

The major predictor of the health of a watershed is the percentage of impervious cover found within its boundaries. Impervious cover is any surface that does not allow water to soak through it, such as asphalt surfaces, concrete surfaces, houses and buildings. It is estimated that watersheds with impervious cover over more than 10% of their area will experience declines in stream quality. When impervious cover exceeds 60%, the stream quality will be severely damaged.

Impervious cover affects watersheds in a variety of ways. By blocking the movement of precipitation into groundwater, stream flow decreases since many streams are fed in part from groundwater. Impervious cover also increases the amount of stormwater entering streams, which can lead to increased flooding, can change the shape of stream channels and can lead to increased erosion. In addition, the amount of pollutants washed into streams, in the form of bacteria, pesticides and herbicides, oil and gas and sediment, increases. This is usually accompanied by a decrease in the biodiversity of a region as both aquatic and terrestrial habitat is impacted.

Development of land and waterways has threatened a variety of ecosystems through out the United States, specifically because of impacts to the water-shed. For example, salmon runs in the streams of the Pacific Northwest have decreased drastically due to watershed development diminishing the health of streams where the salmon spawn. Coral reefs in the Florida Keys have been damaged due to coastal development resulting in pollution and sedimentation in stormwater runoff. Rare salamanders found in Texas springs have become endangered due to poor land use practices affecting aquatic habitat in the watershed.

In general, a group of basic management tools that work at the watershed level can mitigate some of the threats to stream quality. These tools include watershed planning, land conservation, maintaining ecological buffers such as wetlands, improved site design, erosion management and mitigation, stormwater treatment, control of water discharges not related to storms, and long-term watershed monitoring. Because of both the ecological and human dependence on watersheds, the improvement of watershed management practices is becoming recognized as a priority by local, regional, and national governments.

See also Hydrologic cycle; Water pollution.

Resources

BOOKS

Grossman, E. Watershed: The Undamming of America. Boulder: Counterpoint Press, 2002.

OTHER

Center for Watershed Protection. Home Page. November 29, 2006 <http://www.cwp.org/> (accessed November 30, 2006).

United States Environmental Protection Agency. Wetlands, Oceans, and Watersheds. November 28th, 2006. <http://www.epa.gov/owow/> (accessed November 30, 2006).

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Watershed

Watershed

A catchment or drainage basin that is the total area of land that drains into a water body. It is usually a topographically delineated area that is drained by a stream system. River basins are large watersheds that contribute to water flow in a river. The watershed of a lake is the total land area that drains into the lake. In addition to being hydrologic units, watersheds are useful units of land for planning and managing multiple natural resources . By using the watershed as a planning unit, management activities and their effects can be determined for the land area that is directly affected by management. The hydrologic effects of land management downstream can be evaluated as well. Sometimes land use and management can alter the quantity and quality of water that flows to downstream communities. By considering a watershed, many of these environmental effects can be taken into consideration.

See also Watershed management

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Watershed

Watershed

A watershed refers to land that is drained by an interconnected system of rivulets, streams, rivers , lakes, and groundwater . Water from a watershed eventually drains into a common destination. Both rain and snow contribute to the watershed. Coastal watersheds that begin as rivulets often end as large rivers that empty into a lake or an ocean . Watersheds can range in size from just a few square miles to many hundreds, even millions of square miles.

A catchment or drainage basin , which is the total area of land that drains into a water body, is usually a topographically delineated area that is drained by a stream system. River basins are large watersheds that contribute to water flow in a river. The watershed of a lake is the total land area that drains into the lake. In addition to being hydrologic units, watersheds are useful units of land for planning and managing multiple natural resources. By using the watershed as a planning unit, management activities and their effects can be determined for the land area that is directly affected by management. The hydrologic effects of land management downstream can be evaluated as well. Sometimes land use and management can alter the quantity and quality of water that flows to downstream communities. By considering a watershed, many of these environmental effects can be taken into consideration.

Watersheds are important as habitats for many creatures, and as a source of drinking and recreational water for many communities. As well, because one watershed can often by connected to another watershed that lies "downstream," the environmental quality of one watershed can affect other watersheds. As more communities rely on watersheds for their drinking water, the preservation of watersheds is becoming more urgent.

To function properly, a watershed needs to be maintained in a fairly undisturbed state, especially near watercourses. This undisturbed habitat helps to keep unwanted pollutants and excess soil and runoff from reaching the water course. The preservation of watershed habitats is recognized as a priority by local, regional, and national governments.

See also Hydrologic cycle; Water pollution.


Resources

books

Grossman, E. Watershed: The Undamming of America. Boulder: Counterpoint Press, 2002.

organizations

Center for Watershed Protection. 8391 Main Street, Ellicott, MD, 213043-4605. (410) 461–8323. <http//www.cwp.org/>.

United States Environmental Protection Agency, Office of Wetlands, Oceans, and Watersheds (4501T). 1200 Pennsylvania Avenue, NW, Washington, DC 20460. <http://www.epa.gov/owow/>.

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