The thermal characteristics of hydrologically intact Type C and E streams in eastern Oregon

Graduation date: 2003Many streams in eastern Oregon are listed as water quality impaired on the\ud basis of water temperature. However, it is often difficult to predict water\ud temperature for these streams even if there are no anthropogenic impacts. We\ud measured air and water temperature and stream characteristics on three Type C and\ud E channel streams to determine if stream type can help predict stream thermal\ud characteristics. All six streams were hydrologically intact, assessed as Proper\ud Functioning Condition (PFC), and were located in eastern and south central\ud Oregon.\ud Water and air temperatures and stream geomorphic data were taken during\ud the summer months of 1998 and 1999. Average daily maximum and minimum\ud water temperature and average daily maximum and minimum rates of change in\ud water temperature following normalization of data with estimated water residence\ud time were analyzed. There was more variation within stream type than across\ud groups, which precluded separation of stream types based on thermal\ud characteristics. Most streams regardless of type and year exhibited similar daily mean nighttime recoveries of approximately 0.53°C/hour cooling in the\ud downstream direction following normalization by water residence time. All of the\ud streams heated at least 1.0°C/hour during the day with some streams gaining\ud 2.25°C/hour in the downstream direction following normalization by water\ud residence time. Thermal variation among the streams was likely a result of the\ud daily initial water temperature, the gradient between stream and thermal\ud environment, and the varied physical character of each stream within type.\ud Atmospheric temperature is probably the single most critical factor for\ud characterizing stream temperature behavior during the periods of heating and\ud cooling