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The Problem McNary Dam on the Columbia River is the first mainstem dam downstream of the Snake and Columbia river confluence. Subyearling fall chinook salmon emigrate past McNary Dam in the summer when water temperatures approach the upper incipient lethal maximum. The combination of high air temperatures, little or no wind-induced mixing of surface waters, and the starting and stopping turbine units contribute to the establishment of strong thermal gradients in the gatewells at McNary Dam that collected fish must pass through. The effect is most pronounced at the southern end of the powerhouse where forebay surface waters are the warmest. This thermal challenge the fish face may be compounded by the addition of physical stress associated with the bypass system. The long-term consequences of such chronic exposures to sublethal temperatures is unknown, but may manifest itself in high mortality at dams due to disease caused by Flexibacter columnaris, physical stress during passage, and the induction of heat stress proteins. Objectives The objectives of this study are to 1) define the magnitude and importance of the thermal challenges that fish experience as they pass through the McNary fish collection system, 2) understand how warm surface waters are entrained into the powerhouse so that corrective actions can be taken, and 3) determine the effects of operations on collection system temperatures. Methodology
This project uses an array of thermographs to monitor water temperatures in the forebay of McNary Dam and the fish collection system. Thermograph strings were deployed on the trash racks covering turbine intakes to characterize the vertical thermal profile of water being drawn into the powerhouse. Tests were conducted to determine the effect of starting and stopping turbine units on collection system temperatures. Thermographs recorded water temperature responses during these tests, and juvenile fall chinook salmon fitted with temperature-sensing radio tags provided residence time and thermal exposure information. We measured physiological variables to describe the effects of high water temperature on juvenile fish. We collected liver samples for stress protein analysis periodically throughout the summer, and we also conducted fish health exams to describe the incidence of disease in the general population. Highlights and Key Findings
Thermal gradients in the forebay of McNary Dam are established on hot, calm days when water temperatures in the top 1 m of the water column can exceed 26°C. This warming is more pronounced in the southern portion of the forebay. Turbine units draw water from this end of the forebay when they are running. When a turbine is started, the fish collection system is flooded with warm water which takes a number of hours to dissipate. The thermal exposure of fish in the collection system rapidly increases at this time. Fish sampled for stress proteins, which can indicate thermal stress, generally showed little response in 2001 and 2002 indicating that they were not exposed to high temperatures for extended periods of time or were able to avoid them. This was also evidenced in their low incidence of disease in both years. Where Are We Headed In 2003 This study will continue its third year in the summer of 2003. A primary focus this year will be conducting laboratory experiments to determine the temperature conditions necessary to induce stress proteins in juvenile fall chinook salmon and their long-term effects. In addition, fish will be challenged with the pathogen Flexibacter columnaris to determine the role of temperature in contracting this pathogen. We will continue to monitor fish collection system temperatures and conduct experiments at McNary Dam to better understand how powerhouse operation influences temperature gradients so that solutions can be found to minimize the negative effects on fish. Project Contact Kenneth Tiffan Email: ken_tiffan@usgs.gov Publications |
