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NW Fishletter #373, September 5, 2017
 Riverkeeper: No Sustained Hot Water Temps if Lower Snake Dams Go
If the lower four Snake River dams did not exist, the river would have been cool enough for salmon migration during summer 2015, according to a modeling performed by Columbia Riverkeeper.
However, that conclusion is questioned by others, including Northwest RiverPartners and NOAA Fisheries.
During summer 2015, several hundred thousand adult sockeye, steelhead and spring/summer Chinook--a small number of them endangered and threatened populations from the Snake River Basin--died during two months of consistently high water temperatures.
A record run of nearly 2,000 endangered sockeye were expected to pass Lower Granite Dam on the lower Snake River that year, but instead only 440 made it to the dam on their way to Idaho's Salmon River basin.
The Riverkeeper study said its modeling shows that the four lower Snake River dams caused the sustained warm water temperatures in July and August of 2015.
The model was created by the EPA in 2001 to study the temperature of the Columbia and Snake rivers. Called RBM-10, it considers water velocity, water depth and surface area, air temperatures, and numerous other factors to predict river temperatures under varying conditions.
Despite record-breaking air temperatures and low flows during the summer of 2015, the study concluded, a "free-flowing lower Snake River would have remained cool enough for salmon to migrate successfully."
In the debate about what to do about the river's high water temperatures, some experts have emphasized that even without dams, the lower Snake River would still exceed 68 degrees in the summer.
"Indeed, our modeling showed that a free-flowing lower Snake River would have briefly exceeded 68 degrees on two occasions in 2015, but would have returned to temperatures consistent with salmon migration within a few days; whereas the dammed lower Snake downstream of Lower Monumental Dam remained above 68 degrees from late June to early September," the study said.
Columbia Riverkeeper "supports removal of the Snake dams so it is no surprise that their analysis concludes the dams need to be removed to reduce water temperatures," said Terry Flores, Northwest RiverPartners executive director, in an email to NW Fishletter.
"Even they admit the model is simple and one-dimensional, which means it is highly reliant on the assumptions used," she said.
Michael Milstein, a spokesman from NOAA Fisheries, indicated that he, too, was skeptical. "Given the unprecedented air temperatures in 2015, many of the tributaries were feeding unusually warm water into the mainstem, warming it as it continued downstream," he said in his email to Fishletter.
NOAA's postmortem of the 2015 sockeye migration on the Columbia and Snake rivers pointed to these unprecedented conditions.
Milstein said a 2001 modeling study by Pacific Northwest National Laboratory looking at temperatures in the Snake River with and without dams concluded "that the impoundments kept water cooler later in the spring and that overall there were only relatively small differences in temperature between an impounded and unimpounded river."
Miles Johnson, a coauthor of the Riverkeeper study, said in an email that his research focused on "what dam removal might accomplish in terms of water temperature in the lower Snake River during an extremely hot, dry year--similar to conditions we expect to see more often as climate change intensifies."
The PNNL 2001 study and an EPA study in 2002 "were more general and not as focused on climate change," Johnson said.
The Riverkeeper RBM-10 model indicated that as water moved downstream through each of the four dams' reservoirs in the lower Snake, river temperatures increase about 2 degrees, the study said. This figure is consistent with EPA's previous findings of water temperatures in each lower Snake reservoir rising about 2-4 degrees.
The PNNL study, using a model called MASS1, indicated Snake River water temperatures would increase about 1 degree Celsius (or about 1.8 F).
While a free-flowing river would flush warm water downstream and cool the river, the reservoirs' slow-moving water retains heat, the Riverkeeper study said.
NOAA Fisheries' review of 2015 conditions said what was observed during that summer were prolonged periods of water above 68 degrees, causing fish migration delays and mortalities associated with delay.
But Milstein said the temperatures highlighted in the Riverkeeper study were taken in the tailrace, which is right below the dam.
"These are not the coolest temperatures in the reservoirs and likely not representative of where the sockeye migrate. They likely migrate in the cooler water in the reservoir, near the bottom, which exists because of the reservoirs," the NOAA spokesman said.
Milstein also pointed to the U.S. Army Corps of Engineers' new temperature-control structure at Lower Granite Dam and a similar structure to be installed at Little Goose Dam that cool water in the fish ladders.
Regarding differing water temperatures in the Snake River system, study coauthor Johnson said, "some parts of the river are probably warmer than average (like fishways and forebays) while other parts may be cooler than average (deep spots)."
He also noted that the one-dimensional RBM10 model only looks at average river temperatures.
"It's my understanding that the Corps will publish some two-dimensional modeling of temperatures in the lower Snake River as part of the EIS for the new BiOp, so that that should shed more light on these issues," he said.
Flores characterized the Riverkeeper study as "hardly a convincing analysis to argue for Snake dam removal, a draconian action given the benefits these dams provide."
The lower Snake River modeling study was conducted by Johnson, a biologist and Columbia Riverkeeper's clean-water attorney, and Matthew Shultz, a former software engineer, now a Ph.D. student at Stanford University working on predictive water-quality modeling. -Laura Berg
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