Updates to CE-QUAL-W2 models for select U.S. Army Corps of Engineers reservoirs in the Willamette Valley Project and an inter-reservoir reach of the Middle Fork Willamette River, northwestern Oregon

First posted September 5, 2023 For additional information, contact: Director, Oregon Water Science CenterU.S. Geological Survey601 SW Second Avenue, Suite 1950Portland, 97204 Mechanistic models capable of simulating hydrodynamics and water temperature in rivers reservoirs are valuable tools for investigating thermal conditions their relation to dam operations streamflow river basins where upstream storage management decisions have an important influence on reaches with threatened fish populations. In particular, allow managers investigate how new, untried or hypothetical structures might downstream. CE-QUAL-W2 is a two-dimensional (laterally averaged) hydrodynamic water-quality model that has previously been used the downstream effects other anthropogenic influences stream Willamette River Basin northwestern Oregon, region two populations species designated as under Endangered Species Act. By linking upstream, large Valley Project dams reservoirs, these can be at individual integrated system. Integrated simulations include linked help develop better understanding tradeoffs associated potential retrofits operational changes across multipurpose Project, effect tributaries River, resulting habitat conditions.River corridors from U.S. Army Corps Engineers were updated simulate occurred March through October 2011 (a cool wet year), 2015 hot dry 2016 moderately year) using version 4.2. These encompass following:Coast Fork Middle Rivers, Row Fall Creek Cottage Grove, Dexter, Dorena, Dams, respectively;South McKenzie Cougar Dam;McKenzie its confluence South River;South Santiam Foster Dam;North Big Cliff Dam; andWillamette start Coast Rivers Falls (river mile 26.0; near West Linn, Oregon).This report documents modifications, boundary condition data sources estimation methods, goodness-of-fit statistics six reservoir one existing models. (1) Hills Lake; (2) Lookout Point Lake Dexter Reservoir River; (3) reach between Dam downstream; (4) (5) Green Peter (6) Detroit (7) North River. built by variety researchers range past years; this upgrade Survey (USGS) edition 7 4.2 updates each January December 2011, 2015, 2016. Also included explanation modifications source code constitute USGS Each described run isolation “system model” (or) whole.As part report, some parameters adjusted improve stability decrease error, including meteorological, hydrologic, inputs developed years 2016, necessary. cases, drive previous versions no longer available, which required development checking new techniques. Goodness-of-fit outflow simulated generally show good fit, subdaily temperatures most comparable locations mean absolute error less than 1 degree Celsius (°C) reasonably low bias. Model simulation vertical profiles also produced overall °C all 3 years, exception when did not fill (2015 2016). Both known calibration issues tend sensitive choice certain structural model. Overall, process was focused obtaining settings led realistic predictions (2011, 2016) without over-calibrating specifically any single year. A complete investigation submodels beyond scope but could undertaken future if performance desired.