What Is A Watershed?

We all live in a watershed.and the flow of water as it crosses the land can be a beautiful part of the way we live.  Growing Green Communities is committed to educating people about their watershed and the role we can play in protecting and enhancing its health.

The U.S. Environmental Protection Agency devotes a portion of its website to educational training sessions called the Watershed Academy. These informational modules answer many common questions about watersheds and explain the importance of watershed protection and conservation.


What is a watershed?

It's the area of land that catches rain and snow and drains or seeps into a marsh, stream, river, lake or groundwater.  Homes, farms, ranches, forests, small towns, big cities and more can make up watersheds. Some cross county, state, and even international borders. Watersheds come in all shapes and sizes. Some are millions of square miles; others are just a few acres. Just as creeks drain into rivers, watersheds are nearly always part of a larger watershed.  


Effects on watersheds

Low-density residential suburbs and office parks might not seem to create much impervious surface, but they are served by roads, services such as shopping centers, recreational centers, schools, utilities and their associated parking lots, which together add up to increased impervious surfaces.  For example, a parking lot might be 95 percent impervious, a residential lawn might be 40 percent impervious and natural land covers are nearly 0 percent impervious (Anacostia Restoration Team 1991). Imperviousness results in fundamental changes in the characteristics of land cover.  

In terms of the hydrologic cycle, less water is infiltrated and more runs off at the surface. This is an important point because the effective impervious surface in a watershed affects the physical structure of streams and waterbodies, as well as the diversity and abundance of aquatic life. It is also related to the amount of pollution caused by human activities that is transported directly to waterbodies in storm events, rather than being filtered through soil.


Water Quality and Habitat Impacts

Increased vehicle use, roads, construction site sediment runoff and residential trash and waste are all potential sources of concern for waterbodies during urbanization and post-urbanization. Greater paved surface area per capita results in increases of nonpoint source pollution from vehicles, pets and lawn care activities. Impervious surface can lead to the following:

§         Disturbance of forests, soils, and wetlands that once served as buffers and filters

§         Destruction of habitat for fish and wildlife and impaired aquatic health

§         Increased nutrient pollution in waterways, causing algal blooms and eutrophication

§         Thermal flashes and damaging temperature ranges in streams and creeks

§         Contamination of drinking water sources

§         Increases in polluted runoff from human and household sources

§         Decreased ground water recharge


Watershed Protection

A Watershed Protection Approach is a strategy for effectively protecting and restoring aquatic ecosystems and protecting human health. This strategy has as its premise that many water quality and ecosystem problems are best solved at the watershed level rather than at the individual waterbody or discharger level.

Major features of a Watershed Protection Approach are:

§         Targeting priority problems,

§         Promoting a high level of stakeholder involvement,

§         Integrated solutions that make use of the expertise and authority of multiple agencies

§         Measuring success through monitoring and other data gathering.

Community growth and management strategies should allow for the following:

§         Periodic revision of master plans to reflect evolving community visions and goals

§         Mainstreaming of innovative landscape design modifications, such as low-impact development techniques, and traditional patterns of development (i.e., New Urbanism) that help to achieve watershed protection goals.

§         Updating of zoning ordinances that use outdated justifications or rely on historical conventions, such as parking lot requirements that have excess capacity in areas that offer transit alternatives.


Smart Growth

An important element of smart growth is the redevelopment and infill of existing urban areas. Many cities have reinvested in older sites that offer connections with existing infrastructure such as road systems and riverfronts. Cleaning up and using these areas often helps to preserve green space and other environmental infrastructure such as wetlands, which might otherwise be developed to accommodate growth. Using brownfields can help save natural lands from sprawl by redeveloping existing urban infrastructure into new urban uses such as shops, commercial buildings and entertainment complexes. For every acre of brownfields redeveloped, it is estimated that an average of 4.5 acres of greenfields are saved (Deason et al. 2001).

An important component of smart growth is design at the site level. In terms of street design, there are opportunities to create choices for transportation other than automobiles. Adding trees can help regulate the urban heat island effect, improve urban air quality and retain stormwater. Another smart growth technique for street design involves the incorporation of natural drainage systems.

A characteristic of natural drainage systems is that they also have associated vegetation and wildlife, thereby improving the aesthetic value of the streets on which they are installed. They help to meet multiple planning goals-community amenities, wildlife habitat, water resource management and aesthetic value.

Low-impact development (LID) is another aspect of smart growth that ties in well with water resource management. Natural approaches to stormwater management, soil amendments, vegetated swales, green roofs, bioretention areas, and raingardens are just some of the techniques that fall under the umbrella of this innovative approach.

LID can support smart growth development and retrofitting of existing urban areas to improve watershed management. However, LID should be only part of the smart growth solution to a community's growth management issues. LID does not replace local land use planning; rather, it is a set of tools to better manage stormwater from areas appropriately designated for growth.