This exercise is for an undergraduate elective course in hydrology covering groundwater and surface water.

A background on how discharge is measured (and why it is useful) is helpful for this exercise but it is not necessary - the activity can stand on its own.

This is a lab exercise designed to take up to three hours (most students are finished in less time).

1. Gain proficiency in finding and using USGS discharge data;
2. Understand how long-term flood frequency is calculated;
3. See how a simple flood map can be drawn using discharge data.

See the limits of conventional flood-frequency analysis

Learn enough for a passing familiarity with Excel graphs, ArcGIS, and digital elevation models.

This activity is designed to occupy a typical three-hour lab period, although it can be finished in less time. Partly the time required depends on the students' familiarity with computers - Web browsers, Excel and ArcGIS are all required for this exercise. In a nutshell, the activity can be divided into several parts:
1. Students spend some time on the USGS website examining the different ways the data can be accessed, and look at the data for a river that they are all familiar with.
2. Some of the peak discharge data for a site on the Walla Walla river is put into Excel and analyzed with simple flood-frequency methods. For this lab we do not go into more detail.
3. Using a USGS DRG and a DEM in ArcGIS, students make a simple map showing inundation area near the gage at flood stage. (Alternatively, you could have students make their map for one of the discharges they can identify from their rating curve.)

Student handout for discharge lab (Acrobat (PDF) 104kB May28 13)
Student handout for discharge lab (Text File 18kB Apr15 13)
GIS data for assignment (Zip Archive 4.8MB Apr15 13)

I have provided my own copy of this activity, which instructors will certainly want to modify to fit their own courses. For those instructors who work with LaTeX, my original .tex source is available, I used Philip S. Hirschhorn's "Exam" document class. If you do not use this program, I have provided the .pdf so that the document will at least be readable to you.

The old version of this assignment was written using ArcGIS 9, but I have modified the exercise to work with ArcGIS 10. As a rule, I don't try to explain too much of ArcGIS in my hydrology course, so this part is somewhat "cookbook." At my institution there is a data server where students can access the elevation data for this part; you will certainly need to modify this for your institution.

Note that the GIS flood inundation map is "wrong" in that it predicts that floodwaters are flat, when in reality they have a slope. The GIS implementation of a sloping surface is more complex and I leave it out, but make sure your students understand the limitations of this method.

This lab is assessed on the basis of (1) student answers to questions in the packet, (2) the rating curve and flood frequency graphs the students made in Excel, and (3) the inundation map the students make in ArcGIS.

The USGS real-time streamflow data site: http://waterdata.usgs.gov/nwis/rt. This data is necessary to use the assignment.