Temperature prediction using energy budget techniques on small mountain streams

Graduation date: 1967This study is part of the Alsea Basin Logging-Aquatic Resources\ud Study research program. It was initiated to determine the applicability\ud of energy budget theory to stream temperature prediction on small\ud forested streams. The study was also designed to evaluate the energy\ud budget technique as a tool in the management of mountain streams\ud for the production of high quality water.\ud Temperature predictions were made on four stretches of three\ud streams in the Coast and Cascade Ranges in Oregon during the summers\ud of 1965 and 1966. Three of these stretches were forested.\ud The fourth was completely exposed to direct radiation.\ud Stream temperature change occurring within a stretch of\ud stream was determined by evaluating the radiative, evaporative,\ud and conductive fluxes incident at the surface of the water as it moved\ud down stream. Net radiation was measured directly. Evaporation was\ud computed using a Dalton type equation. Conduction was determined with the Bowen ratio. These fluxes were then added to determine\ud the net flux. Stream temperature change was computed as: [see pdf for equation]\ud Stream temperature was predicted with varying degrees of\ud accuracy on the four stretches. Tests suggested that the predictions\ud could be improved slightly on long stretches by subdivision of the\ud stretch and by separating data into daytime or nighttime units. Additional\ud tests indicated that under a broken canopy. net radiation estimates,\ud and thus stream temperature predictions, may be improved\ud by measuring, or utilizing in the predictive equation, only the diffuse\ud radiation penetrating the canopy. Integration of the net radiation\ud recorded to include occasional spots of sunlight results in an overestimation\ud of temperature change during sunny periods.\ud A stream bottom may act as a heat sink during the day and as\ud a heat source at night. This phenomenon was measured on one\ud stretch. This helped explain predictive errors of about 10° F.\ud The study on the open stretch showed that during the day, conductive and evaporative fluxes were small compared to the\ud radiative flux. This led to modification of the original formula for\ud predicting temperature maxima. This formula is:\ud [see pdf for equation]\ud This permits field personnel to make estimates of maximum\ud temperature changes attainable by opening a stretch of stream