Generalization of stream-temperature data in Washington
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 lowflow periods, summer-minimum river temperatures were raised and occur 4 days earlier than they would under natural conditions. Bl B2 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES STREAM TEMPERATURE DATA IN WASHINGTON B3 Collings and Higgins (1972) presented stream-temperature data for the State of Washington in maps of the amplitudes, maximums, minimums, and medians of stream temperature. PURPOSE AND SCOPE Objectives of this study were to: (1) statistically describe and define the relation between natural stream temperatures and the topographic and climatic drainage-basin characteristics that are most effective in explaining the site-to-site variations in those stream temperatures, (2) present a procedure to estimate water temperatures at sites where little or no stream-temperature data are now available, and (3) use selected examples to show how the effect of water impoundment on natural stream temperatures may be evaluated. Stream-temperature data were investigated for more than 400 sites; about 300 of these were west of the Cascade Range. Temperature data for the main stem of the Columbia River were omitted from this report because the river has unique or anomalous stream temperatures compared to those of most other rivers in the State and because a complex individual stream-temperature study of the Columbia River is beyond the scope of this report.