Although water levels fluctuate in nature, hydroelectric project operations can cause water level fluctuations beyond what naturally occur in rivers, and that may strand various life stages of fish or other aquatic species, and/or alter invertebrate production and community diversity. Juvenile fish may be particularly susceptible to stranding mortality. Under certain circumstances, flow fluctuations may also result in indirect impacts, such as temporary loss of habitat from dewatering, dewatering of redds leading to reduced reproductive success, loss of food resources, increased predation, and behavioral responses that could reduce survival or growth. Several approaches for evaluating the effects of flow fluctuations on aquatic resources are used by researchers, the most common of which are discussed below, including hydraulic modeling, direct observation, experimental net enclosures, and macroinvertebrate assessments. The following references provide a good overview of the effects of flow fluctuations at hydropower projects:
Hunter, M. A. 1992. Hydropower flow fluctuations and salmonids: a review of the biological effects, mechanical causes, and options for mitigation. Technical Report No. 119. State of Washington Department of Fisheries, Olympia.
R2 Resource Consultants. 2005. Effects of pulse type flows on benthic macroinvertebrates and fish: a review and synthesis of information. Prepared by RD Resource Consultants, Inc., Redmond, Washington and Pacific Gas & Electric Company, San Ramon, California.
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