Modeling streambed heating in shallow streams

The Oregon Department of Environmental Quality is developing Total Maximum Daily Loads to address water quality concerns and threatened and endangered species habitat requirements. Approximately 940 water body segments are listed as water quality limited for temperature in Oregon. CE-QUAL-W2 Version 3 is a two-dimensional water quality and hydrodynamic model capable of modeling rivers, reservoirs and estuaries. An important aspect of modeling stream temperature is handling the short-wave solar radiation that penetrates the water surface and impacts the streambed, which can affect water temperatures under low-flow conditions. The Bull Run River-Reservoir system is a 264 km2 watershed 42 km east of downtown Portland and serves as the city's primary drinking water source. A dynamic, three-dimensional streambed heat transfer model was developed and calibrated with field data from the Lower Bull Run River and laboratory experiment data. Model results compared well to field data from bedrock and cobble substrates. The model calibration for the cobble substrate revealed the substrate interstitial water temperature played a large role in the substrate temperatures and was necessary to calibrate the model. The streambed heating model compared welt with the laboratory experiments' data in many cases. The model was compared to two analytical models and a one-dimensional model for various application cases and performed well.;The streambed heating model was implemented in CE-QUAL-W2 and a sensitivity analysis examined the impacts of river flows, substrate type and streamside shading. Water temperature impacts focused on daily minimum and maximum temperatures. Increased flow rates resulted in decreased water temperature impacts from streambed heating. The largest water temperature impacts occurred with the bedrock streambed with decreasing impacts once cobble was incorporated. Increased streamside shading reduced the impact of streambed heating. General guidelines were discussed when streambed heating may be an important part of the surface water heat budget.;The clear-sky solar radiation model in CE-QUAL-W2 was compared to four models and calibrated to data from 17 sites around the U.S.A. to identify improvements in predicting clear-sky solar radiation. A dynamic vegetative and topographic streamside shading model was included to more accurately simulate the effective solar radiation striking the water surface.