53:171 Water Resources Engineering
Problem #7
Flow Duration Curves Before and After Dam Construction

Coralville Reservoir was completed and became operational in 1958.  Before that time, the flows on the Iowa River at Iowa City (USGS 05454500) were unregulated.  Since then, the flow conditions at Iowa City are largely determined by releases from the reservoir.

Use the daily flow data to examine the changes in the flow duration curve at this site, before and after the dam's construction.  The daily flow data can be downloaded directly from the USGS web site. Go to USGS Surface-Water Data for the Nation page and select the Daily Data.

1. Evaluate the flow duration curve using data daily through 1957/12/31.  Plot the flow duration curve for the "before" case.
2. Evaluate the flow duration curve using data daily from 1958/01/01 to 2011/09/30.  Plot the flow duration curve (on the same plot as before).
3. We discussed in class what changes one would expect before and after dam construction.  In what ways do the comparison meet this expectation (what makes sense).  In what ways does it not meet this expectation (what does not make sense).  Please speculate on the possible reasons for an outcome that does not meet your expectation.