Urbanization and Streams: Studies of Hydrologic Impacts
Hydrologic impacts due to urbanization are reported to cause water quality problems such as sedimentation, increased temperatures, habitat changes, and the loss of fish populations. Although there is widespread recognition that these problems are caused by increased runoff volumes and velocities from urbanization and associated increases in watershed imperviousness, much of the reported information has been anecdotal. The summaries and analyses of reports and case studies in this report are intended to go beyond the anecdotal and provide documentation of problems and sources, as well as a foundation for further investigation.
Planners, engineers, water quality specialists, and government officials should find this study a useful introduction to understanding the potential hydrologic impacts of urbanization on streams.
This report was derived from a literature search to find and document physical impacts and indications of water quality problems. United States Geological Survey reports; American Water Resources Association publications; federal, state, and local agency reports; journal articles; conference proceedings; and consultations with experts provided the documentation and case study examples cited in this report.
Examination of published literature revealed a large amount of anecdotal information that identifies hydrologic impacts on streams caused by increased impervious area (e.g., roads, driveways, parking lots, and rooftops) in urban developments. Figure 1 graphically depicts the impacts of urbanization on stream flow documented in the literature, and Table 1 summarizes the relationship between these changes in flow and other impacts in receiving streams. These impacts include increased frequency of flooding and peak flow volumes, increased sediment loadings, loss of aquatic/riparian habitat, changes in stream physical characteristics (channel width and depth), decreased base flow, and increased stream temperature.(1)
1. For more information on impacts on streams due to urbanization, refer to the following: Fundamentals of Urban Runoff Management (Horner et al., 1994), Site Planning for Urban Stream Protection (Schueler, 1995), Effects of Urbanization on Aquatic Resources (Klein, no date), Environmental Indicators to Assess Control Programs and Practices (Claytor and Brown, 1996), Clearing and Grading Strategies for Urban Watersheds (Corish, 1995), and several articles in Watershed Protection Techniques (Center for Watershed Protection).
Table 1. Impacts from Increases in Impervious Surfaces.
|Increased Imperviousness leads to:||Resulting Impacts|
(e.g., inadequate substrate, loss of riparian areas, etc.)
|Erosion||Channel widening||Streambed alteration|
|Increased peak flow||*||*||*||*||*|
|Increased peak flow duration||*||*||*||*||*|
|Increased stream temperature||*|
|Decreased base flow||*|
|Changes in sediment loadings||*||*||*||*||*|
Nine case studies that contained quantitative documentation linking urbanization to hydrologic impacts on streams were identified. They are summarized in Table 2 and are described in the appendix in more detail. It should be noted that some of the impacts identified in Table 2 are inferred from the presence of other indicators. For example, the Valley Stream, Pines Brook, and Bellmore and Massapequa creeks case studies from Long Island, New York, revealed a significant decrease in stream base flow resulting from increased urbanization within the contributing watersheds. Although habitat loss, average stream temperatures, and low dissolved oxygen concentrations were not reported in the study, these impacts typically occur as a result of decreased base flow and can be assumed (Horner et al., 1994; Klein, no date).
Table 2. Results of Case Study Reviews
|Case Study||Location||Documented Impacts||Inferred Impacts|
|Pheasant Branch Basin||Middleton, WI||
|Holmes Run Watershed||Fairfax, VA||
|Peachtree Creek||Atlanta, GA||
|Pipers Creek||Seattle, WA||
|Valley Stream, Pines Brook, Bellmore Creek, and Massapequa Creek||Nassau County, NY||
|East Meadow Brook||Nassau County, NY||
|Kelsey Creek||Bellvue, WA||
|Several Creeks||Dekalb County, GA||
|Patuxent River System||Maryland||
There are documented case studies that conclusively link urbanization and increased watershed imperviousness to hydrologic impacts on streams. Existing reports and case studies provide strong evidence that urbanization negatively affects streams and results in water quality problems such as loss of habitat, increased temperatures, sedimentation, and loss of fish populations.
However, relatively few case studies have assembled detailed quantitative information to document these phenomena. This is due, in part, to (1) the heavy reliance on engineered approaches to runoff management that can transfer hydrologic impacts (e.g., habitat loss, flooding, channel widening, and erosion) to downstream areas through the construction of paved channels, stormwater pipes, and bank stabilization (e.g., riprap, cutbacks, plantings, bulkheads) and (2) the difficulty and high costs associated with long-term watershed monitoring. Furthermore, the installation of drainage structures, such as pipes and concrete channels, is the final step in removing urban streams from the landscape. Classically, many of these activities have resulted in urban streams being "written off" as virtually nonexistent; therefore, the resulting impacts on water quality and habitats are being ignored.
It is anticipated that in the future the literature will be supplemented with additional studies that document the relationship between urbanization, impervious surfaces, and problems in streams. Future investigations might include Federal Emergency Management Agency (FEMA) floodplain management activities. FEMA trend analysis of widespread changes in 100-year floodplain delineations or increased claims for financial assistance in specific watersheds might add increased evidence of hydrologic impacts due to urbanization. In the meantime, it is hoped that existing information proves sufficient to allow planners, engineers, and local officials to recognize potential hydrologic impacts due to urbanization and to take steps to prevent water quality problems while allowing for sensible development.
Claytor, Richard A., and Whitney E. Brown. 1996. Environmental Indicators to Assess Stormwater Control Programs and Practices. Prepared by the Center for Watershed Protection, Silver Spring, Maryland, in cooperation with the U.S. Environmental Protection Agency.
Corish, Kathy. 1995. Environmental Land Planning (ELP) Series: Clearing and Grading Strategies for Urban Watersheds. Metropolitan Washington Council of Governments, Washington, DC.
Horner, Richard R., Joseph J. Skupien, Eric H. Livingston, and H. Earl Shaver. 1994. Fundamentals of Urban Runoff Management: Technical and Institutional Issues. Prepared by the Terrene Institute, Washington, DC, in cooperation with the U.S. Environmental Protection Agency.
Klein, Richard D.. (No date). Effects of Urbanization Upon Aquatic Resources. Report by the Tidewater Administration, Maryland Department of Natural Resources.
Schueler, Thomas. 1995. Environmental Land Planning Series: Site Planning for Urban Stream Protection. Prepared by the Metropolitan Washington Council of Governments and the Center for Watershed Protection, Silver Spring, Maryland.
Schueler, Thomas. 1987. Controlling Urban Runoff: A Practical Manual for Planning and Designing Urban BMPs. Metropolitan Washington Council of Governments, Washington, DC.
U.S. Environmental Protection Agency. 1995. Economic Benefits of Runoff Controls. U.S. Environmental Protection Agency, Office of Wetlands, Oceans and Watersheds, Washington, DC.
Barbour, Michael T., Jerome Diamond, and Christopher Yoder. 1996. Effects of Watershed Development and Management on Aquatic Ecosystems. SETAC Press, Pensacola, Florida.
Driver, Nancy E., and Gary D. Tasker. 1990. Techniques for Estimation of Storm-Runoff Loads, Volumes, and Selected Constituent Concentrations in Urban Watersheds in the United States. U. S. Geological Survey Water-Supply Paper 2363. U.S. Geological Survey, Washington, DC.
James, Williams. 1995. Modern Methods for Modeling the Management of Stormwater Impacts. Computational Hydraulics International, Guelph, Ontario.
Jones, R. Christian, and Donald P. Kelso. 1994. Bioassessment of Nonpoint Source Impacts in Three Northern Virginia Watersheds. George Mason University, Fairfax, Virginia.
Leopold, Luna B. 1994. A Field Example: Watts Branch. In A View of the River, pp. 148-167. Harvard University Press, Cambridge, Massachusetts.
Mead, Estyn R. (Date unknown). Addressing Hydrologic Modification and Habitat Loss: Tools to Assess the Impacts of Hydrologic Modification on Aquatic Communities. U.S. Fish and Wildlife Service, Division of Habitat Conservation, Arlington, Virginia.
Newbury, Robert. 1995. Rivers and the Art of Stream Restoration. In Natural and Anthropogenic Influences in Fluvial Geomorphology, pp. 137-149. Newbury Hydraulics Ltd., Gibsons, British Columbia, Canada.
Sauer, V.B., W.O. Thomas, Jr., V.A. Stricker, and K.V. Wilson. 1983. Flood Characteristics of Urban Watersheds in the United States. U.S. Geological Survey Water-Supply Paper 2207. Prepared by the U.S. Geological Survey in cooperation with U.S. Department of Transportation, Federal Highway Administration.
Schueler, Thomas R. 1994. The Stream Protection Approach: Guidance for Developing Effective Local Nonpoint Source Control Programs in the Great Lakes Region. Prepared by theCenter for Watershed Protection, Silver Spring, Maryland, in cooperation with the U.S. Environmental Protection Agency.
Spinello, Anthony G., and Dale L. Simmons. 1992. Base Flow of 10 South-Shore Streams, Long Island, New York, 1976-85, and the Effects of Urbanization on Base Flow and Flow Duration. USGS Water Resources Investigations, Report 85-4068. Prepared by U.S. Geological Survey in cooperation with Nassau County Department of Public Works and Suffolk County Department of Health Services.
Yoder, Christopher, and Edward Rankin. 1995. Biological criteria program development and implementation in Ohio. In Biological Assessment and Criteria: Tools for Risked-based Planning and Decision Making, ed. W.S. Davis and T. Simon. CRC Press/Lewis Publishers, Ann Arbor, Michigan.
Finley, Stuart. Lake Barcroft Watershed Improvement District, Fairfax County, Virginia.
Henry, William. Northern Virginia Soil and Water Conservation District, Fairfax, Virginia.
Muncy, Joy. U.S. Army Corps of Engineer, Fort Belvoir, Virginia.
Powell, Rocky. Baltimore County Department of Environmental Protection, Baltimore, Maryland.
Shreeve, Robert. Maryland Department of Highway Administration, Annapolis, Maryland.
Turlinger, Margaret. Waterways Experiment Station, U.S. Army Corps of Engineers, Vicksburg, Mississippi.
City of Fairfax, Department of Environmental Resources, Fairfax, Virginia.