- Despite escalating conflict over fresh water, recent years have witnessed a growing realisation that human society must modify its behaviour to ensure long-term ecological vitality of riverine ecosystems. In response, ecologists have been increasingly asked to guide instream flow management by providing ‘environmental flow’ prescriptions for sustaining the ecological integrity of riverine systems.
- Environmental flows are typically discussed in the context of water releases from dams and water allocation for extraction (such as for urban use or irrigation), where there is general agreement that rivers need to exhibit some resemblance of natural flow variability necessary to support a functioning ecosystem. Although productive dialogue continues on how best to define environmental flows, these discussions have been focused primarily on water quantity without explicit consideration of many components of water quality, including water temperature – a fundamental ecological variable.
- Many human activities on the landscape have modified riverine thermal regimes. In particular, many dams have modified thermal regimes by selectively releasing hypolimnetic (cold) or epilimnetic (warm) water from thermally stratified reservoirs to the detriment of entire assemblages of native organisms. Despite the global scope of thermal alteration by dams, the prevention or mitigation of thermal degradation has not entered the conversation when environmental flows are discussed.
- Here, we propose that a river’s thermal regime is a key, yet poorly acknowledged, component of environmental flows. This study explores the concept of the natural thermal regime, reviews how dam operations modify thermal regimes, and discusses the ecological implications of thermal alteration for freshwater ecosystems. We identify five major challenges for incorporating water temperatures into environmental flow assessments, and describe future research opportunities and some alternative approaches for confronting those challenges.
- We encourage ecologists and water managers to broaden their perspective on environmental flows to include both water quantity and quality with respect to restoring natural thermal regimes. We suggest that scientific research should focus on the comprehensive characterisation of seasonality and variability in stream temperatures, quantification of the temporal and spatial impacts of dam operations on thermal regimes and clearer elucidation of the relative roles of altered flow and temperature in shaping ecological patterns and processes in riverine ecosystems. Future investigations should also concentrate on using this acquired knowledge to identify the ‘manageable’ components of the thermal regime, and develop optimisation models that evaluate management trade-offs and provide a range of optimal environmental flows that meet both ecosystem and human needs for fresh water.
The U.S. Department of the Interior’s Bureau of Reclamation (Reclamation), established in 1902, is best known for the dams, power plants, and canals it constructed in the 17 western states that led to homesteading and promoted the economic development of the West. Reclamation has constructed more than 600 dams and reservoirs including Hoover Dam on the Colorado River. Reclamation is the second largest producer of hydroelectric power in the United States. Its 58 power plants annually provide more than 40 billion kilowatt hours annually, generating nearly a billion dollars in power revenues, and producing enough electricity to serve six million homes.In October 2006, Reclamation awarded a contract for the modernization of the 26 hydroelectric generating units at Hoover, Davis, and Parker Dams on the lower Colorado River. Hoover Dam power generation is used to meet load regulation requirements and fast, predictable, repeatable unit control provides significant benefits. The project upgrades all unit control and protection equipment, replacing some equipment dating back to the 1940s that was not easily maintainable.Unique about this project was that Reclamation elected to obtain a commercial solution based on demonstrated success by the vendor in recent similar projects rather than issuing the traditional custom design specification. The vendor was to use commercially available components and previously proven designs. Reclamation identified work boundaries, conceptual requirements and objectives stating that cutting-edge technologies and custom solutions would not be considered.L&S Electric, Inc. (Rothschild, Wis.), was awarded a $5.7 million contract for the modernization project to upgrade the existing mechanical governors to digital, install new digital generator and transformer protective relays, install new programmable-logic-controller-based unit controls, and replace static pilot exciters with new digital equipment. L&S Electric was responsible for system integration, engineering and equipment modernization, and was required to standardize the hardware design for all 26 units. Twenty months after the contract was awarded, the first six upgraded units were operational. This is no small feat considering that similar automation projects based on traditional government specifications have taken five to 10 years from award to operation.The benefits received from just eight of 26 upgrades have already improved power system control. Power system oscillations caused by rapid changes in demand during heavy summer power requirements were reduced during the summer of 2008 using the improved unit control responses. Significant improvements are expected in operating efficiency (power produced from water delivered) as the remaining upgrades are completed.
Many river restoration projects are focusing on restoring environmental flow regimes to improve ecosystem health in rivers that have been developed for water supply, hydropower generation, flood control, navigation, and other purposes. In efforts to prevent future ecological damage, water supply planners in some parts of the world are beginning to address the water needs of river ecosystems proactively by reserving some portion of river flows for ecosystem support. These restorative and protective actions require development of scientifically credible estimates of environmental flow needs. This paper describes an adaptive, inter-disciplinary, science-based process for developing environmental flow recommendations. It has been designed for use in a variety of water management activities, including flow restoration projects, and can be tailored according to available time and resources for determining environmental flow needs. The five-step process includes: (1) an orientation meeting; (2) a literature review and summary of existing knowledge about flow-dependent biota and ecological processes of concern; (3) a workshop to develop ecological objectives and initial flow recommendations, and identify key information gaps; (4) implementation of the flow recommendations on a trial basis to test hypotheses and reduce uncertainties; and (5) monitoring system response and conducting further research as warranted. A range of recommended flows are developed for the low flows in each month, high flow pulses throughout the year, and floods with targeted inter-annual frequencies. We describe an application of this process to the Savannah River, in which the resultant flow recommendations were incorporated into a comprehensive river basin planning process conducted by the Corps of Engineers, and used to initiate the adaptive management of Thurmond Dam.