WATERSHEDS - Watersheds consist of all surface water and include lakes, streams, reservoirs, and wetlands, as well as all groundwater and aquifers. The water in a watershed originates via precipitation that is collected on the surface and groundwater. At the boundaries of watersheds, there are drainage divides usually in the form of ridges or hills. As people take water out of a river for irrigation and other city-wide uses, the river's flow decreases and with this decreased flow, natural river cycles such as flooding, may not occur. This could, in turn, hurt ecosystems depending on the river's natural cycles.

........................................................................................

Watersheds

Overview of Watersheds and Watershed Management

by Amanda Briney

A watershed, also called a "drainage basin" in North America, is an area in which all water flowing into it goes to a common outlet, such as the same estuary or reservoir.

Watersheds themselves consist of all surface water and include lakes, streams, reservoirs, and wetlands, as well as all groundwater and aquifers.

The water in a watershed originates via precipitation that is collected on the surface and groundwater.

However, it is important to note that not all precipitation falling in an area exits the watershed. Some of it is lost through evaporation and transpiration, some is used by people and some soaks into the soil and groundwater.

At the boundaries of watersheds, there are drainage divides usually in the form of ridges or hills. Here the water flows into two separate watersheds and does not always end up in a common outlet.

In the United States, for example, there are many different watersheds, but the largest is the Mississippi River basin which drains water from the Midwest into the Gulf of Mexico. This water does not enter the Pacific Ocean because the Rocky Mountains act as the drainage divide.

The Mississippi River basin is an example of an extremely large watershed, but watersheds vary in size.

Some of the world's largest ones contain smaller watersheds within them depending on where the final water outlet is.

Types of Watersheds

The second is called a major drainage divide. In this situation, waters on each side of the boundaries do not meet via the same river or stream, but they do reach the same ocean.

For example, there is a drainage divide between the Yellow River (Huang He) basin and the Yangtze River in China but both have the same outlet.

The final type of drainage divide is called a minor drainage divide. In these, waters separate at the divide but later rejoin. An example of this situation is shown with the Mississippi and Missouri Rivers.

Key Features of a Watershed

The second feature is the drainage divide or watershed boundary, such as a mountain range. This plays a role because it helps in determining whether the water in the watershed is flowing toward or away from an area.

The next feature is the topography or terrain of the watershed's land. If the area is steep, the water there is likely to flow quickly and cause flooding and erosion, whereas flat watersheds have often had slower flowing rivers.

The final feature of a watershed's physical landscape is its soil type. Sandy soils, for example, absorb water quickly, while hard, clay soils are less permeable. Both of these have implications for runoff, erosion, and groundwater.

Significance of Watersheds

By studying the key watershed features in addition to activities along waterways scientists, other researchers and city governments can work to keep them healthy because a small change in one portion of a watershed can drastically affect other parts.

Human Impacts on Watersheds

Watershed pollution occurs in two ways: point source and nonpoint source.

Point source pollution is pollution that can be traced to a specific point such as a disposal site or leaking pipe. Recently, laws and technological advances have made it possible to detect point source pollution and its problems are being reduced.

Nonpoint source pollution occurs when pollutants are found in water running off of crops, parking lots and other lands. In addition, it can also be caused when particulates in the atmosphere fall onto the land with precipitation.

Humans have also impacted watersheds by reducing the amount of water flowing within them.

As people take water out of a river for irrigation and other city-wide uses, the river's flow decreases and with this decreased flow, natural river cycles such as flooding, may not occur. This could, in turn, hurt ecosystems depending on the river's natural cycles.

Watershed Management and Restoration

Watershed restoration, on the other hand, is aimed at restoring already impacted watersheds to their natural state through the monitoring of pollution and regulations to reduce further pollution.

Watershed restoration programs also work often to repopulate the watershed with its native plant and animal species.

Amanda Briney

·   Professional geographer, writer, and scholar

·   More than 10 years of experience writing about a broad array of geographical topics

·   Holds three university degrees and an advanced certificate in GIS 

Experience

Amanda Briney is a professional geographer and writer who contributed to ThoughtCo for more than 10 years. She wrote countless articles on a wide range of topics such as an introduction to the subject of geography, reviews of ecotourism, discussions about environmental determinism, and the structure of Latin American cities. The scope of her work also includes other formats such as histories, guides, and fact sheets about many parts of the world. An ultimate scholar, Amanda also contributes work to academic venues and the GIS Lounge, an informational portal about geography.

Amanda enjoys all aspects of geography and mapping but is especially interested in examining natural landscapes through spatial analysis. As such, she holds a certificate in Geographic Information Systems (GIS) from California State University. She also attended Diablo Valley College where she studied air photo interpretation and the formation of the Earth's landscapes.

Education

Amanda Briney received a Master Arts (M.A.) in Geography from California State University–East Bay. She also holds a Bachelor Arts (B.A.) in English and Geography from California State University–Sacramento and a earned a Certificate of Advanced Study in Geographic Information Systems (GIS) from California State University.

ThoughtCo and Dotdash

ThoughtCo is a premier reference site focusing on expert-created education content. We are one of the top-10 information sites in the world as rated by comScore, a leading Internet measurement company. Every month, more than 13 million readers seek answers to their questions on ThoughtCo.

For more than 20 years, Dotdash brands have been helping people find answers, solve problems, and get inspired. We are one of the top-20 largest content publishers on the Internet according to comScore, and reach more than 30% of the U.S. population monthly. Our brands collectively have won more than 20 industry awards in the last year alone, and recently Dotdash was named Publisher of the Year by Digiday, a leading industry publication.

https://www.thoughtco.com/what-are-watersheds-1435367