Stream Dynamics and the Urban Environment

Anne Larson Hall
Environmental Studies at Emory University
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This field activity focuses on stream dynamics and urban development. Students determine stream discharge and observe riparian conditions for a local wadeable urban stream. After the field trip, students delineate the watershed boundary, analyze satellite images of the watershed, and use online USGS stream data is used to make comparisons between forested and urban stream response to storm events.

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This activity is used in a 200-level introductory geology course in an Environmental Studies department that has both social and natural science course requirements. This course fulfills a general education lab science requirement for all students, and an earth science focus-area requirement for our majors. There is a mix of roughly one-third majors and two-thirds non-majors in the course.

Skills and concepts that students must have mastered

Students should have a basic understanding of the water cycle and how the urban environment affects the water cycle, for example, that an increase in impervious surfaces increases runoff and decreases infiltration. A discussion in the field will clarify the data that is needed to calculate stream discharge, though the students will think this through on-site. Students should be familiar with reading topographic maps in order to delineate the watershed boundary, analyzing satellite images, and will learn to draft a storm hydrograph and calculate lag time ~ these activities are used to supplement the field trip.

How the activity is situated in the course

This is a stand-alone exercise to reinforce lecture material on stream dynamics and urban development.


Content/concepts goals for this activity

  • Students will develop an understanding of factors that affect stream discharge.
  • Students will know how to measure the data for the stream discharge equation, Q = AV.
  • Students will develop an understanding of the ways in which urban development affects stream dynamics and alters natural services provided by stream ecosystems.

Higher order thinking skills goals for this activity

Analysis of data ~ students will analyze their own stream discharge data, especially with regard to sources of error, and compare their data with online USGS stream discharge data for a storm event on the field site stream and for a stream in a forested areas.
Formulation of hypotheses ~ students will predict how urban development would affect stream discharge during storm events.

Other skills goals for this activity

Students will write up field reports, use a flow probe to determine stream velocity, measure cross-sectional area of a stream, sketch a stream reach and include relevant data and observations, complete activities working in groups and after the field trip delineate a watershed on a topographic map, analyze satellite images of the watershed, and use online U.S.G.S. stream data to draft storm hydrographs and calculate lag time.

Description of the activity/assignment

This field activity focuses on stream dynamics and urban development. The field site is a local, wadeable urban stream and the activity, including transportation, can be completed during a 3-hour lab session. At the field site, a sketch of the stream reach is drafted by each student. This sketch includes a visual representation of the stream channel and banks as well as written observations, such as the amount of riparian vegetation, evidence of erosion and type of stream sediment. In small groups, students then determine stream velocity and cross-sectional area at the site, and calculate stream discharge (Q= velocity x cross-sectional area). In the field, there is discussion of the causes of changes in stream discharge (change in input/output), the relationship between the factors in the stream discharge equation (channel dimensions, velocity) and the effects of urban development on streams.

After the field trip, given a topographic map of the area, students delineate the stream's watershed boundary. Students analyze the satellite image of the watershed to determine land use patterns. Students use online USGS data to draft a storm hydrograph and determine lag time for this stream after a rain event (video and photos of this stream at normal and flood stage are posted on the class website). The students also compare data from a stream in a nearby national forest during a similar storm event, noting differences in the storm hydrograph and lag time.

Determining whether students have met the goals

  • Students will hand in a field trip report that demonstrates that they have successfully measured cross-sectional area and velocity of the stream and have calculated stream discharge.
  • Students will complete a neatly drafted sketch of the stream reach with relevant written observations.
  • Students will be able to discuss the differences in stream dynamics between the urban and forested streams.
  • Students will be able to analyze their data for sources of error (groups will compare data for the same stream reach on the same day).
  • Students will get into the stream (wearing fashionable hip boots)!
  • After the field trip: Students will be able to draft storm hydrographs and calculate lag time for an urban and a forested stream. Students will be able to use satellite images to determine land use patterns.

More information about assessment tools and techniques.

Teaching materials and tips

Other Materials

Supporting references/URLs

Excellent chapter "How to have a field day surveying streams" in Stream Hydrology: An Introduction for Ecologists by Nancy D. Gordon, Thomas A. McMahon, Brian L. Finlayson, Christopher J. Gippel and Rory J. Nathan. Wiley Press.

The Scientific Imperative for Defending Small Streams and Wetlands
Research sponsored by American Rivers and the Sierra Club.

Physical, Chemical, and Biological Responses of Streams to Increasing Watershed Urbanization in the Piedmont Ecoregion of Georgia and Alabama, 2003 ~ By M. Brian Gregory and Daniel L. Calhoun

Links on Impervious Surfaces ~ The NEMO (Nonpoint Education for Municipal Officials) Program

Source for Flow Probe

USGS Water Data (more info)

U.S.G.S. Reports on Urban Streams
Aquatic Life Declines at Early Stages of Urban Development

Effects of Urbanization on Stream Ecosystems

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