Temperature Effects of Point Sources, Riparian Shading, and Dam Operations on the Willamette River

Animation of Model Results

This animation of model results shows modeled water temperatures and modeled cumulative point-source temperature changes along the Coast Fork Willamette River downstream of Cottage Grove Dam (river miles above 187) and the entire length of the Willamette River. Additional details are described below.

Cumulative Point-Source Heating Effects

The Willamette flow and temperature models were run to quantify the Natural Thermal Potential (NTP) conditions specified by the Willamette temperature TMDL. The NTP model run included restored riparian vegetation and no point sources of heat to the modeled rivers. The NTP model run is the TMDL's baseline condition, against which the cumulative heating effect of the point sources is compared. The NTP model results are shown in the graph and the movie as the "No Point Sources" or NTP results.

A second set of model scenarios was run to quantify the cumulative heating effect of the point sources. This model run was created by adding the point sources to the NTP model run, and is degnated in the graph and the movie as "All point sources" or "WLA." All model results were analyzed by computing the modeled 7-day moving average of the daily maximum (7dADM) water temperature for every location, then computing the 7dADM temperature difference due to the point sources. The final result (on the last frame of the movie) is a 95th percentile of the modeled temperature differences as a function of location along the river, computed according to methods described elsewhere.

The lower graph shows the modeled 7dADM temperatures from the NTP (Natural Thermal Potential baseline, no point sources), and the WLA (all point sources) model runs, in blue and red, respectively. Also shown on the lower graph are the locations of tributary inflows (blue squares) and point sources (red triangles). Finally, the State of Oregon maximum water temperature criteria for the protection of sensitive fish species is shown with a black line. According to the State of Oregon temperature standard, if the NTP modeled temperatures should exceed the standard's numeric criteria, the NTP temperatures become the criteria for the temperature standard at that time. When that occurs, human-caused temperature increases are limited to 0.3^oC, an amount called the Human Use Allowance.

The upper graph shows the modeled 7dADM temperature difference due to the modeled point sources using a heavy black line. The thin blue lines keep track of the minimum and maximum temperature differences since the beginning of the animation, for those periods that are included in the final computation of the 95th percentile of the modeled 7dADM temperature differences. For more details, see the analysis methods page.

See the full report for more details and discussion:

Rounds, S.A., 2007, Temperature effects of point sources, riparian shading, and dam operations on the Willamette River, Oregon: U.S. Geological Survey Scientific Investigations Report 2007-5185, 34 p.
[Available online at: http://pubs.usgs.gov/sir/2007/5185/]