Water Quality - Temperature

Introduction WQ Operations Map Water quality is important for the health of aquatic species, including ESA-listed fish. The Agencies operate the Basin to manage total dissolved gas Libby and Hungry Horse dams in (TDG) and temperatures in the rivers. The Agencies also monitor other water quality Montana, and Dworshak in parameters such as nutrients, potassium, pH, conductivity, dissolved oxygen, and all have reservoirs that stratify and others. have selective withdrawal structures to release warmer or cooler water for Which Reservoirs Can Help Manage Temperatures? downstream temperature management. Temperature influences Some reservoirs stratify (warm water stays on top, while cold water sinks to the are strongest immediately downstream bottom). Water from these reservoirs can sometimes be used to help manage of the dam but lessen as this water temperature conditions for aquatic species downstream. Depending on the time of travels farther downstream. year, warmer or cooler water can be released to help manage downstream temperatures. Other reservoirs are isothermal (temperature is nearly the same from top to bottom). These reservoirs cannot be used for temperature management downstream. Changes in Reservoir Temperature Over Time Some reservoirs are stratified in the summer and isothermal in the fall and Dworshak Reservoir Franklin D. Roosevelt Reservoir () winter, which can limit the Agencies’ ability to manage downstream temperatures. 1600 1290 Air 1574 Air 1280 Stratified Reservoir with Isothermal Reservoir 1549 1270 1524 SelecSelectivetive WithdrawalWithdrawal 1260

Selective Withdrawal Structure 1499 GateGate OperaOperationtion Range Range 1250

1474 1240

Warmer Sun warms upper Warmer levels of the 1449 1230 (ft ) (ft ) 1424 1220 on reservoir on Power Plant Intake Elevation 1399 1210 eva ti eva ti 1374 1200 El Selective Withdrawal El rvoir Temperature ese rvoir 1349 Temperature ese rvoir 1190 R Structure can pull water R 1324 1180 from different elevations 1299 1170

to mix temperatures 1249 1160 Third Power Plant Intake Elevation 1199 1150

1149 1100

Warm water 1099 1050 Left and Right Power Plant Intake Elevation Colder Colder from high in 1049 1000 Ja n Ja n Ja n the reservoir Ja n 01 -Jul 15 -Jul 03 -Jul 09 -Jul 17 -Jul 24 -Jul 31 -Jul 16 -Oct 15 -Apr 04 -Apr 17 -Apr 28 -Apr 10 - 17 - 31 - 15 - 01 -Jun 15 -Jun 05 -Jun 12 -Jun 19 -Jun 26 -Jun 15 -Nov 15 -Dec 14 -Feb 21 -Feb 04 -Mar 13 -Mar 27 -Mar 15 -Feb 15 -Mar 01 -Aug 15 -Aug 01 -Sep 15 -Sep 06 -Aug 14 -Aug 15 -May 01 -May Warm water 08 -May 15 -May 22 -May 29 -May can mix with cold water from deep Dworshak Reservoir stratifies in the summer with warm and In an average year, the Columbia River flow at Grand Coulee in the cool water accessible through the dam’s selective withdrawal Dam is enough to fill the project approximately eight times. reservoir gates. Dworshak is used in the summer months to help cool With the high volume of water that flows through the reservoir, temperatures on the lower . the pool weakly stratifies. Grand Coulee Dam has two elevations from which to draw water into three power plants. At these elevations the temperatures are very similar throughout the year. In early summer the outflows from Grand Coulee Dam are typically cooler than the inflows to the reservoir near the border with Canada. Cold water