Effects of hypothetical management scenarios on simulated water temperatures in the Tualatin River, Oregon

Water temperature is one of the most important factors determining the health of fish and other aquatic organisms. If water temperatures warm beyond a critical threshold, particularly during the sensitive life stages of fish, survival can markedly decrease. In 1996, the State of Oregon adopted a revised maximum water temperature standard of 17.8 C (degrees Celsius) (64 F [degrees Fahrenheit]) for most waterways, including the Tualatin River in northwestern Oregon. To assess water temperature conditions in the Tualatin River, a recent cooperative study between the U.S. Geological Survey and the Unified Sewerage Agency ofWashington County, Oregon, used two dynamic-flow heat-transport models, DAFLOWBLTM (river mile [RM] 63.9-RM 38.4) and CEQUAL-W2 (RM 3 8.4-RM 3.4). After the models were calibrated with data collected during the 1994 low-flow season, they were used to simulate various hypothetical water-management scenarios. Results from the first 10 scenarios were published in an earl