USING USGS STREAMFLOW DATA TO DESIGN CLASS PROJECTS THAT COMBINE INDEPENDENT AND COLLABORATIVE RESEARCH

Streamflow data have several advantages for engaging students. 1) Streams are important and visible parts of our dynamic environment. 2) Stream gages are abundant and sample watersheds with a variety of sizes and differing geologic and land-use characteristics. 3) Basic hydrologic data from stream gages (peak annual flows and mean daily flows) are available on-line from the USGS and can easily be downloaded and processed in a spreadsheet. 4) The abundance of gages makes it possible to design student projects of some depth that involve both independent and collaborative components. This presentation will describe two designs for projects appropriate for environmental geology, hydrogeology, or water resource courses. One, which uses historical daily streamflow to investigate decadal climate change, will be detailed on the poster. The other is described in some detail here.

Peak annual flows form the basis of flow frequency analysis, and the “(N+1)/R” method for estimating recurrence is fairly well known. I ask each student to use data from a different stream gage to determine the 10-year, 50-year, and 100-year flows for their gage using Excel. Then, I ask them to pool their data and to graph the flows (logarithmic y-axis) vs. the area of each gage’s contributing watershed (logarithmic x-axis). Their main job is to discuss this graph and its implications. Students can discover or be led to recognize the power law relationship between any x-year flow and area, and they can fit a trend line to find it. But, they will also see that the model doesn’t fit flows from some gages very well. Discussion leads them to consider why: urbanization, dams and other controls, and other climatic, geographic and geologic factors may be considered. Maps and the USGS website provide food for thought. The endpoint of the discussion is the concept of regional models for streamflow frequency, the means by which gage information is made more generally useful.