REVIEW OF LITERATURE
As watershed protection
issues have quickly gained momentum in rising to the top of the list of
the most pressing environmental issues of today, urban sprawl and development
have emerged as the leading threats to water quality. Before a discussion
on the effects of development on urban watersheds can begin, it is essential
to first "lay the groundwork" for the discussion by discussing the fundamentals
of watersheds and urban sprawl. As there are numerous organizations, agencies,
and individuals who conduct water-based research, there are just as many
definitions for what a watershed is or isn't. According to the United States
Environmental Protection Agency (EPA), a watershed is "the area of land
that catches rain and snow and drains or sweeps into a marsh, stream, river,
lake or groundwater." Further, the Center for Watershed Protection (CWP)
defines it as "an area that, due to its natural drainage pattern, collects
precipitation and deposits it into a particular body of water." The CWP
goes on to explain that in the Western region of the U.S., these areas
are often referred to as "drainages" while in other regions they are called
The Watershed Information Network (WIN) provides a definition that states "watersheds are nature's boundaries. They are the areas that drain to water bodies, including lakes, rivers, estuaries, wetlands, streams, and the surrounding landscape." An even more detailed and complex definition of a watershed is provided by a group known as Ontario Streams who suggests that a watershed is "a three dimensional landscape that is a direct product of local climate and geography." Despite the elementary nature or the complexity of the definition, it is suggested that the best description of a watershed was given by a scientist/geographer by the name of John Wesley who said that a watershed is "that area of land, a bounded hydrologic system, within which all living things are inextricably linked by their common water course and where, as humans settled, simple logic demanded that they become part of a community ." Regardless which definition one chooses to adopt, the fact that watersheds are indispensable to the well being of virtually every living being remains unchanged.
Not only are watersheds critical when it comes to safe drinking water, they also play an important role in issues ranging from agricultural run-off to sewage treatment. Now that a solid foundation for the understanding of watersheds has been established, it is only fitting that one for urban sprawl be developed. As no universally accepted definition of "sprawl" has been created to date, various meanings abound; just as with the term "watershed." The Vermont Forum on Sprawl has decided that "dispersed development outside of compact urban and village centers along highways and in rural countryside" is an accurate definition for the term. Renowned policy analyst Anthony Downs defines sprawl by its traits which include unlimited outward extensions, low-density residential and commercial settlements, leapfrog developments, dominance of transportation by private automotive vehicles, and reliance mainly on the trickle-down or filtering process to provide housing to low-income households.
Sprawl is the result of many factors. In a recent article found in American Forests, author Dan Smith cites the decline in livable cities, public subsidy of services and infrastructure in suburban areas, and rapid population growth as a few of these factors. As the fundamental aspects of watersheds and urban sprawl have been explored, the discussion on the effects of development on urban watersheds can commence. Many studies have been conducted in varying regions of the United States in an attempt to examine the relationship between land development and water quality .In a study conducted in what was a predominantly agricultural Midwestern watershed, but that also had some forests and urban development, it was observed that land use had a distinct overall and seasonal effect on stream water quality (Osborne and Wiley, 1988). Additionally, a study in the New Jersey Pinelands showed substantial land use effects on natural water quality which were related to agricultural development, urban density, and domestic wastewater flow (Bolstad and Swank, 1997). As developmental pressures hold crucial implications for water quality, the results of one study suggests that these pressures often result in adverse affects on water quality. It is concluded that removal of riparian vegetation, as well as alteration of organic inputs and hydrologic regimes by forest and agricultural activities and expanding urbanization, generally results in increased erosion, increased algae production, changes to temperature regimes, and reduced concentrations of dissolved oxygen (Welch et al. 1998).
Patterns of land use undoubtedly serve as useful indicators of overall water quality. In a 1995 study conducted by C. T. Hunsaker and D.A. Levine, in Illinois and Texas it was found that the percentage of land in forests and other uses were the best predictors of general water quality. Similarly, while working in the Southern Appalachians, Bolstad and Swank found that the percentage of land in non-forest cover and the density of paved roads were among the most important variables influencing water quality. Studies on impervious surfaces have also shown a correlation between urban sprawl and watershed quality. As these surfaces, which include roads, parking lots, rooftops, sidewalks, and other impermeable surfaces that would be characteristic of an urban setting, collect and accumulate pollutants that are leaked from vehicles, deposited from the atmosphere, or derived from other sources, during rain or snow these pollutants are quickly washed off and rapidly delivered to aquatic systems. Monitoring and modeling studies have consistently indicated that urban pollutant loads are directly related to watershed quality (Schueler, 1994). To further support the theory that development directly impacts watersheds, in his article entitled "The Importance of Imperviousness," Tom Schueler states that even relatively low levels of urban development result in high levels of bacteria derived from urban run-off or failing septic systems. As such, run-off pollution is considered the major cause of water quality problems in most urban watersheds (Schueler and Swann). Various "everyday" behaviors can contribute to run-off pollution including leaf disposal/composting, landscaping, sidewalk/driveway sweeping, and watering/irrigation (Schueler and Swann). This type of knowledge can be extremely useful in identifying where land use is most likely to be intensified within a watershed, remain the same, or change in insignificant ways. Each of these studies, as well as others that have not been discussed within this review, lean toward the common conclusion that it is difficult to maintain predevelopment stream quality once watershed development has begun.
Bolstad, P.V. and W.T. Swank. "Cumulative Impacts of Land Use on Water Quality in a Southern Appalachian Watershed." Journal of the American Water Resources Association 33.3 (1997): 23 May 2000 <http://www.srs.fs.fed.us/pubs/rpc/1998-06/rpc_98iun_06.pdf>.
Center FAO's. Center for Watershed Protection. 7 Aug. 2000
Hunsaker, C.T. and D.A. Levine. "Hierarchal
Approaches to the Study of Water Quality in Rivers." Bioscience. 45: 193-203.
Smith, Dan. "The Case for Greener Cities." AmericanForests 24 Aug. 2000
Swank, W.T. and P.V. Bolstad. Cumulative Efforts of Land Use Practices on Water Quality:409-421. Hydrochemistry. Proceedings of Rostov-on-don Symposium, May 1993. IAHS Publication 219. IAHS Press, Oxfordshire, UK.
The Challenge. Watershed Initiatives. 15
Sept. 1999 <http://www.watershedinitiatives.org/>.
Wear, D.N., M.G. Turner, and R.J. Naiman.
"Land Cover Along an Urban-Rural Gradient:Implications for Water Quality."
Ecological Applications, 8(3). 1998, pp. 619-630.