The effect of water temperature on the ecosystem of streams necessitates an analysis of various physical characteristics that influence stream temperatures. This study was conducted to determine (1) the effective relations that define site-to-site variation in stream temperatures, (2) equations and methods to estimate stream temperatures at sites where little or no data are now available, and (3) a procedure to evaluate the effect of water impoundment on natural stream temperatures.
Statistical multiple-regression analyses were used to develop equations for relations between stream temperatures and topographic and climatic characteristics of the drainage basins.
Multiple-regression techniques, generally, produced more accurate equations for estimating temperatures of streams in western Washington than for those in eastern Washington. A standard error of estimate was used to show how precisely stream temperatures may be defined by air-temperature and topographic drainage-basin characteristics. Of 24 original parameters tested, 15 were found effective to determine the equations of one or more of the 15 stream-temperature characteristics.
Effects of holding reservoirs on downstream water temperatures may be evaluated by the use of harmonic curves of probable maximum and minimum stream temperatures. By examples, it was shown that (1) below a hydroelectric-power dam winter-minimum river temperatures were raised and occur 9 days later than they would under natural conditions; and (2) below a flood-control dam, which also augments natural flows during low-flow periods, summer-minimum river temperatures were raised and occur 4 days earlier than they would under natural conditions.