Estimated and measured traveltime for the Crow River watershed, Minnesota

A time-of-travel study involving a luminescent dye was done on the Crow River in Minnesota from Rockford to the confluence with the Mississippi River at Dayton on July 11, 2006, at a streamflow of 293 cubic feet per second at Rockford. Dye was injected in the Crow River at Rockford, and traveltime and concentrations were measured at three sampling locations downstream: at the Hanover historic bridge in Hanover, at County Road 116 near St. Michael, and at County Road 12 in Dayton. The results of the measured traveltimes were compared to estimated traveltimes from a previous study of the Crow River and six other rivers in the Upper Mississippi River basin in 2003. Regression equations based on watershed characteristics of drainage area, river slope, mean-annual streamflow, and instantaneous streamflow at the time of measurement from more than 900 stream segments across the Nation were used to estimate traveltimes. Traveltimes were estimated and measured for the leading edge, peak concentration, and trailing edge of tracer-response curves. Estimated traveltimes for the leading edge, peak concentration, and trailing edge at Dayton were 25.3, 28.4, and 35.6 hours, respectively. Measured traveltimes for the leading edge, peak concentration, and trailing edge at Dayton were 33.2, 38.2, and 49.2 hours, respectively, for the 22.4-mile reach. Although traveltimes for the Crow and the Sauk Rivers were underestimated by use of the regression equations, the regression estimates were close enough to measured values to be considered satisfactory; hence, this estimating technique should be applicable in other source-water planning efforts in and near the study area.