Truckee River water flow study released
Emergency crews may be able to respond more effectively to accidental spills in the Truckee River using information from a study by the U.S. Geological Survey, Department of the Interior.
The recently released report describes the results of eight dye-tracing studies made in 1999 along the Truckee River between Tahoe City and Marble Bluff Dam, near Nixon, Nev.
Researchers injected a non-toxic red dye in the river, then measured stream flow travel time, changes in concentration and dispersion of the dye plume at several locations as it moved downstream.
“By studying the movement of the dye, we learn what happens to contaminants that may be introduced into a river either purposely or as the result of an accidental spill,” said E. James Crompton, U.S. Geological Survey hydrologist and author of the report.
The 24-page report may also be able to help water administrators conserve water.
“Administrators will have an idea when they should turn intakes on and off because they will have an idea when the peak contaminants will pass,” Crompton said. “This is another piece of information, a tool, for water pollution managers and planners.”
While the information adds to similar studies that were done in 1980 and 1993, the results may not change how water controllers manage the Truckee River.
“Travel time will be helpful for administrators when releasing water to accommodate certain needs,” said John Sarna, an engineer and spokesman for the California Department of Water Resources. “The study is not directly related to negotiations with the Truckee River Operating Agreement.”
However, the study does relate to stream flow regimes and modeling techniques which are helpful to agencies that maintain or use the Truckee River.
The Truckee Tahoe Sanitation Agency has been watching the flow of the river to maintain minimum dilution requirements for emissions from the wastewater treatment facility.
“(USGS) has done this study several times in the last several years,” said Craig Woods, general manager of the sanitation agency. “I would think that this study could be used for small (particles) or a nitrogen study in the river.”
Crompton added that measurements for the leading edge of the dye would likely represent particles lighter than water, such as petroleum. The heavier substances, those that travel below the surface, have slower travel times, and comprised the trailing edge of the dye.
Crompton said the study depends on the river volume. Travel times will be different when the volume of water changes.
Factors such as stream flow velocity and volume do have an effect on the plants and animals in the river, and in some situations the effects can be adverse.
“My major concern is the lack of ramping flows, where you gradually increase or decrease the flow of the river from the dam,” said Ralph Cutter, a local fly fisherman and author of aquatics books. “If the water drops very quickly you have stranding, invertebrates get stuck in microhabitats and die by the billions. Huge flows also create unsettling, which contributes to erosion.”
Because the volume of the water affects the velocity of the river, Cutter said controlling how the water flows is vastly important.
“Rapid fluctuations are not natural,” he said.
“A lot of instream flow requirements for the Truckee River are based on the amount of water needed to sustain Rainbow and Brown Trout populations,” said Banky Curtis, California Department of Fish and Game regional manager for the Sacramento Valley and Central Sierra region. “In the Truckee River Operating Agreement the Dept. of Fish and Game recommended minimum flows, optimum flows, and maximum flows.”
Curtis said minimum flows are too little to sustain life, optimum flows are when conditions are ideal, and maximum flows are when the volume of water discourages population regeneration.
“Instream flow requirements for Lahontan Trout will be different than those for Rainbow and Brown Trout. Both are very important fisheries. It’s one of the decisions we have to make,” he said.
“Comparisons of flow regimes may shed light on new information,” Crompton said. “Another study will look at the differences between each study and later studies.”
The comparative study may be released as early as this December, Crompton said.
The information may be used by the sanitation agency in expansion plans it has for its filtration plant.
The agency has asked for state funding to help meet proposed standards in the Truckee River Operating Agreement. While the agency meets all California standards for clean water, in periods of low river flow the agency may be required to step-up its filtration capabilities to meet proposed standards.
“This is one part of the puzzle,” Woods said, “a useful piece but still just one part.”
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