WATER TEMPERATURES 0? THE WILLAMETTE RIVER SYSTEM, 19^0 



Owing to an extensive program for development of multipurpose water- 

 use projects on the Columbia River system, tributaries of the lower 

 Columbia River have become extremely important for maintaining the salmon 

 fisheries of the river o 



The Willamette River^ a major tributary of the Columbia River, 

 drains about 11,000 square miles of northwest Oregon lying between the 

 Cascade and Coast Ranges, It empties into the Columbia near Portland, 

 Oregon, Tributaries of the Vifillamette River support significant runs 

 of spring chinook salmon and steelhead. 



Development of water-use and flood-control projects on the Willamette 

 River System is changing the ecology of many of the Willamette streams. 

 Changes in temperature and chemical composition of the water will affect 

 fish populations in the System and must be carefully considered in plan- 

 ning a fishery-management program. According to Fish and Rucker (1950) 

 water temperatures play an important role in the formation and lifting of 

 the Willamette River oxygen block. Vifhere temperatures are already near 

 the upper limit of tolerance for salmonoid fishes, and any increase might 

 present a block to migrating fishes, it is especially important to have 

 thermal data before and after projects are developed. These records virill 

 be useful in locating hatcheries, in selecting races or species of fish 

 for introduction to reservoirs and modified streams, and in predicting 

 water temperatures that v;ill obtain after reservoirs are built. 



The temperature of water discharged from some impoundments can be 

 regulated within limits by manipulation of discharge valves or gates; 

 that is, by spacing several gates at various elevations in a dam, water 

 may be drawn from different depths of the impoundment. In general, the 

 deeper the discharge gate is, the cooler the water will be. Thus it 

 might be possible to favorably alter the temperature of the stream below 

 an impoundment. However, after leaving a reservoir and in continuing 

 to flow downstream, the water is exposed to almost the same thermal 

 influences as an unimpounded stream would encounter (Craig 19U6), In 

 order to study the effect of air temperature and other thermal influences 

 on flowing water, it is planned to install thermographs at intervals 

 along the river below Dorena Dam (near Cottage Grove, Oregon) o This dam 

 has a series of discharge gates at different elevations, permitting the 

 draw-down of cool subsurface water from the reservoir. The thermographs 

 ViTill make it possible to determine the extent of this cooling influence 

 downstream.. 



The primary purpose of this investigation is to study the changes in 

 water temperature resulting from development of projects on the Willamette 

 River System. The investigation will continue for several year, and more 



