TMDL Studies Point to Dams for Higher Temperaturesby Mike O'Bryant
Columbia Basin Bulletin - April 5, 2002
Modeling of the mainstem Columbia and Snake rivers is showing that dams are the primary cause of higher temperatures in the rivers.
But private industry representatives at a recent workshop are still worried that an allocation of temperature loads to pollution sources may still impact their businesses.
The Environmental Protection Agency, along with Oregon, Washington and Idaho, and Columbia Basin tribes are developing Total Maximum Daily Load limits for the two rivers based on existing state water quality standards. Temperatures in the rivers at certain times of year fail to meet those standards.
Although EPA modeling is showing that dams are the main culprit for raising water temperature in the rivers, industry representatives worry that if little can be done to lower temperatures at dams and reservoirs, regulatory agencies may look to point sources (industrial effluent) of temperature to take up the slack.
"Maybe you fear that if we can't regulate others, we'll regulate point sources," said Paul Pickett of the Washington's Department of Ecology. "But they are a very small part."
He added that all point sources have to be modeled in the TMDL because all produce heat, but the modeling has yet to set the allocations.
"We don't have any untoward focus on any group," said Rick Parkin of the EPA. "The main causes of temperature are the dams, then climate change and point sources are way down the list."
Modelers first determined whether temperatures in the rivers exceed water quality standards and, if so, if it is due to human activity. To settle the question, they compared water temperatures in the rivers during the period 1939 to 1956 before most dams were in place to temperatures found in the river between 1976 and 1993 after dams were in place. They found that temperatures exceeded water quality limits four times more often in the later period after dams were in place.
From this information, they determined that the water quality standards as set by the states and tribes is the sum of natural temperatures plus an incremental increase due to human activity. Those standards are 16 degrees Centigrade from the Canadian border downstream on the Columbia River to Chief Joseph Dam; 18 C in the Columbia River from Chief Joseph to Priest Rapids Dam; 20 C in the lower Snake River and the Columbia River downstream of Priest Rapids Dam; and 12.8 C or 17.8 C, depending on spawning and rearing timing, from the Salmon River to the Oregon and Washington border on the Snake River.
Modelers are in the process of determining site potential temperatures for each of 16 reaches between the dams. However, the water warms as it flows through each reach downstream and if just the water quality standard is applied to each reach, by the time the water reached the mouth of the Columbia River, it would exceed the target temperature. So, they have to determine target temperatures in the upper reaches that will result in meeting water quality standards in the lower reaches of the river. Looking at each reach, the EPA has discovered that the reach below Grand Coulee Dam has the greatest potential for improvement.
Modelers are predicting that once allocations are determined, there will still be room for industrial growth, which could include new generating facilities that use large amounts of river water in their operations.
According to Pickett, the missing piece in the process is an implementation plan. That is the responsibility of the states and tribes, he said, and it could take years to work through the process of what implementation would look like. "Then we would have to look at how implementation actions affect temperature," he said. "Implementation could suggest another allocation scheme."
Mary Lou Soscia of the EPA said the same model being used in the TMDL study has been used the last couple of years to determine the effects on temperature in the Snake River resulting from summer releases of water from Dworshak Dam, a U.S. Army Corps of Engineers dam on the Clearwater River. The EPA is also looking at other possibilities, such as different operations at McNary Dam for better mixing of water that could result in lower temperatures.
The EPA expects to release a draft TMDL with loading allocations sometime in May, Soscia said, but not before it holds another workshop once it completes further modeling work. After the draft is released, the EPA will allow a 90-day comment period. A final TMDL could be completed in late 2002.
In addition to the mainstem Columbia and Snake rivers TMDL for temperature, states and the EPA are also working on total dissolved gas TMDLs for the lower Columbia River, the mid-Columbia River and the lower Snake River.
Technical Management Team
Columbia River/Snake River mainstem TMDL
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