Exceedance of Colorado Stream Temperature Standards: the Effects of Effluent and a Warming Climate

Graduate Thesis Or Dissertation

Citations

Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/kp78gg72b

Abstract

Colorado adopted new stream temperature standards in 2007 to prevent anthropogenic influences from negatively affecting aquatic organisms by altering the natural thermal regime of a system. Climate and population change will affect discharge and temperature for both streams and effluent. Since the temperature standards are new to Colorado and affect municipal wastewater treatment plants, two important questions arise. First, where are exceedances of the new temperature standard likely to occur? Second, how might the exceedances change under future climate? Empirical modeling was used to investigate where Colorado stream temperature standards are likely to be exceeded as a function of: 1) the ratio of effluent discharge to stream discharge, 2) the timing of exceedance, and 3) stream reach classification. This study found that wastewater treatment plants at low elevations, discharging to cold-water streams are most likely to exceed new stream temperature standards. Mid-elevations have the largest increase in maximum exceedance of 2-5°C, and the total number of days exceeding in a year. Although effluent often exacerbates exceedances, it sometimes aids in cooling of stream temperatures in the summer.

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