National Water-Quality Assessment (NAWQA) Program

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Effects of Urbanization on Stream Ecosystems

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Streamflow and Water Temperature

• Streamflow is a measure of how much water passes a point in the stream over time. Water temperature is a measure of the hotness or coldness of the water in a stream. Both are important components of water-quality assessments and affect physical, chemical, and biological characteristics of streams. Streamflow affects the transport of chemicals, habitat characteristics, and biological communities in a stream. Water temperature can affect the types of biological communities and chemical reactions in streams. All components (physical, chemical, biological) in a stream can be influenced by changes in the hydrologic regime (characteristic behavior and quantity of streamflow). Streamflow and water temperature can be altered as urban intensity in a basin increases. In this study, patterns of streamflow and water temperature were used to compare sites along a gradient of urban intensity from low to high and to determine the relation to other physical, chemical, and biological factors.

What we measured:
• Stage height (height of the water in the stream) was used to measure streamflow.
• Water temperature at hourly intervals.

When we sampled:
• Streamflow and water temperature were measured continuously in each stream for approximately a one year period, although the length of record may vary among streams within and among study areas.

Field collection protocols:
• Transducers were used to measure stage height and water temperature.
• Transducers were place in each stream near the stream reach that was sampled for habitat and biological communities.
• Transducers were checked and data downloaded on a monthly to bimonthly basis.

Quality assurance and control:
• Stage data from the pressure transducer used in studies conducted in 2003 and 2004 had an accuracy of ± 0.036 meters (0.12 feet) which does not meet the USGS standard for accuracy of stage data which is ± 0.003 meters (0.01 feet) (Sauer, 2002). Although the stage data used in this study is not the level of accuracy normally seen from USGS stage data, the stage data meets the purpose of this study which was to look at patterns of flow variability in streams.

What this data represent:
• Stage data is used to characterize changes in streamflow due to urbanization using measures of overall variability, frequency of change in streamflow (flashiness), and duration of high and low flow conditions after McMahon and others, 2003.
• Temperature data will be used to characterize changes in water temperature due to urbanization using measures of daily water temperature, variability in daily temperature, and relation to changes in streamflow.

McMahon, Gerard, Bales, J.D., Coles J.F., Giddings, E.M.P., and Zappia, Humbert, 2003, Use of stage data to characterize hydrologic conditions in an urbanizing environment: Journal of the American Water Resources Association, vol. 39, no. 6., p. 1529-1546.

Sauer, V.B., 2002, Standards for the analysis and processing of surface water data and information using electronic methods: U.S. Geological Survey Water-Resources Investigations Report 01- 4044, 91 p.


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