The Highs and Lows of the Grande Ronde River (Temperature in the Grande Ronde Watershed)

Rachael Hersh-Burdick

In the Grande Ronde River Basin cold water fish species such as Chinook salmon (Oncorhynchus tshawytscha), rainbow trout (Oncorhynchus mykiss) and bull trout (Salvelinus confluentus) depend upon cooler temperatures for survival. While there is not a fixed number that can be used to accurately quantify the temperatures that are needed for their survival, it is certain that the current water temperatures in the Grande Ronde Basin are hotter than is desirable. Furthermore, it has been shown that these elevated temperatures are not solely the result of climatic changes; thus the anthropogenic effects on regional surface water temperatures are significant (Nowak 2004). The anthropogenic effects in the Grande Ronde region can be divided into three categories: riparian vegetation disturbances, channel morphology disturbances and hydrologic disturbances. Each of these disturbances serves to create higher than normal temperatures in the Grande Ronde River and threaten the cold water fish species that inhabit the river. The Total Maximum Daily Load (TMDL) for the Upper Grande Ronde details the regulations that are currently being used to help minimize anthropogenic impacts. Additionally, the diurnal and longitudinal temperature profiles currently available for the Upper Grande Ronde serve as supporting evidence for the River Continuum Concept (RCC), although there are local disturbances in the continuum created by backwater, slackwaters, land use practices, and inflows from larger tributaries with temperatures significantly different from the mainstem. This summer diurnal and longitudinal temperature profiles will be created for the Lower Grande Ronde and it is predicted that they too will support the RCC, although the daily maximums are predicted to be higher than normal.