Predicting the occurrence of cold-water patches at intermittent and ephemeral tributary confluences with warm rivers

Abstract

AbstractCold water provided by small tributary streams can contribute to thermal heterogeneity in downstream receiving waters, thereby providing important thermal refuge habitat for cold-water aquatic taxa residing in warmer mainstem rivers. We investigated the potential function of small perennial and nonperennial tributary streams, including intermittent and ephemeral channels (some of which were dry) as sources of cold water to warmer receiving rivers. We used random forest analysis to model occurrence of cold-water patches at tributary confluences as a function of watershed and climatic characteristics and tested predictive performance with a 2-y data set of 68 tributary–mainstem confluence zones in northeastern Oregon, USA. Cold-water patches were present in 53% (36 of 68) of the tributary confluences. Of these, 14 occurred at tributaries that had no surface-water flow at the time of sampling. The likelihood of a tributary contributing a detectable source of cold water to a confluence zone during lat...