Abstract

As climate change progresses, mean water temperatures in rivers and streams are likely to increase and with longer and more frequent periods of extreme temperatures. As a result, water temperatures are likely to exceed tolerances of a range of taxa more often, altering aquatic ecosystems. Ameliorating these impacts may require consideration and implementation of novel, innovative management techniques. While some of these may not be feasible now, identifying their potential should be assessed now to plan and facilitate any future implementation of these techniques. Cold-water releases, where cooler bottom waters are released from stratified dams, have the potential to offset some of the effects of this increase in temperature. We reviewed the existing literature to determine the prevalence of cold-water releases for the purposes of modifying temperature regimes in rivers. We identified upper and lower temperature thresholds for fish and sensitive invertebrate taxa from literature, including for individual life-history stages where these were known, and established that many Australian rivers are already exceeding these thresholds, particularly upstream of dams. This situation is likely to deteriorate with climate change, having a substantial impact on freshwater biodiversity. 

Cold-water releases downstream of dams reduced maximum water temperatures significantly in the examples that we investigated. We found that there were very few case studies, in Australia or overseas, where cold-water releases had been attempted or modelled for the purpose of actively lowering stream temperatures. In the feedback we received from southern Australian natural resource managers, there were few who were currently considering using the technique or were aware of the potential benefits of the approach. There was one exception; an agency that is planning to use planned releases to mitigate high temperature conditions to encourage recruitment in a threatened fish species. 

To determine whether cold-water releases are of any value in mitigating high temperature events in the future, many knowledge gaps must be filled before the technique is likely to be feasible. The most urgent of those are the effects of cold-water releases on whole ecosystems, rather than a single species of interest, the existence and use of thermal refuges in Australian river ecosystems, a greater understanding of the temperature cues for fish migration and temperature tolerances of stream biota in general. Until these are addressed, we do not recommend using cold-water releases to ameliorate high stream temperatures. However, the approach may need to be considered for some river systems and become more feasible as climate change progresses, as knowledge gaps are filled, and if new techniques for water releases are developed.  

Please cite this report as:

Cummings, CR, Matthews, TG & Lester, RE 2013, Novel methods for managing freshwater refuges against climate change in southern Australia. Supporting Document 1: Evaluating the utility of cold-water releases (“shandying”) for enhancing the resilience of riverine species, National Climate Change Adaptation Research Facility, Gold Coast, 74 pp. 

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