There are enough pockets of cold water on the Columbia River to provide migrating adult salmon and steelhead a temporary reprieve when the lower Columbia River gets uncomfortably warm, an Environmental Protection Agency study found. But these areas of cooler water likely will not be enough to minimize risks to ESA-listed salmonids as climate change continues to warm the lower river and its tributaries, the agency study indicated.
Released in October, EPA's Draft Columbia River Cold Water Refuges Plan identifies the 12 primary and two secondary tributaries below McNary Dam that provide cool August flows into the Columbia River, determining their importance as cold water refuges based on their size, average August temperatures and average temperature differences compared to the main-stem river. The draft plan then outlines specific actions that can be taken in each tributary to protect, enhance or restore its cold water attributes.
Cold water refuges are places in the river where temperatures are cooler, often due to the plume from a tributary. The EPA says that protecting and restoring them is important to the survival of migrating salmon and the recovery of future salmon populations, and will become even more important as the river warms with climate change.
The plan is designed to help steelhead and fall Chinook, which already use the areas of cold water in warmer years, but will not likely benefit sockeye or summer Chinook, which pass the Bonneville Dam in June and early July. "When the river does warm earlier and coincide with sockeye and summer Chinook runs, as it did in 2015, the use of [cold water refuges] is seen as an ineffective migration strategy for these fish. This appears to be because delayed upstream migration by holding in [cold water refuges] results in exposure to warmer mainstem temperatures during their continued upstream migration as river temperatures continue to heat up," the plan says.
The actions in EPA's draft plan to preserve or enhance the Columbia's cold water refuges range from creating shade and pools in tributaries to working with stakeholders to provide more summer flows through conservation, water exchanges and minimum instream flows.
Releasing cooler water from dams on these tributaries is also identified as a way to maintain or enhance the cold water refuges downstream, the draft plan says. Four of the 12 primary tributaries—the Cowlitz, Lewis, Sandy and Deschutes rivers—have upstream dams that could be held back and later released to provide cooler temperatures in the main stem Columbia, much as Dworshak Dam is used on the Snake River to provide cooler flows for fish in late summer and early fall. "These dams, like the Merwin Dam on the Lewis River, can influence summer temperatures by releasing water from the cooler depth within the storage reservoir and controlling summer release flows during times when flow is lowest, during late July through early September," the plan said.
The plan also calls for action by fishery managers to address fishing in cold water refuges, after finding that fall Chinook and steelhead that do hold back in the colder pools may lose survival benefits due to increased harvest in those areas.
The plan characterizes water temperatures and the amount of available cold water refuges in the lower Columbia River—from the mouth to the Snake River—and the extent that salmon and steelhead use them. Washington and Oregon both established a 20 degree Celsius (68 degree Fahrenheit) maximum temperature for the lower Columbia River. Oregon's standard also calls for cold water refugia sufficiently distributed to allow salmon and steelhead to migrate without negative impacts. Warmer water can lead to higher risk of disease, stress and energy loss.
The plan says that sockeye are most susceptible to warm temperatures, suffering limited mortality at 19 to 20 C, and significant mortality at 20 to 21 C. Steelhead are also susceptible, but avoid high water temperatures by holding back in cold water refuges. Chinook are more tolerant to warm temperatures, and also avoid warmer water by using the refuges. They begin to die when water temperatures are 21 to 22 C.
In an average year, about 65,000 steelhead and 5,000 fall Chinook use cold water refuges during peak use, the plan noted. When runs are good and river temperatures are high between August and September, as many as 155,000 steelhead and 40,000 fall Chinoook use the refuges—not necessarily in the same years, however, it added.
The plan includes a section on the lower Columbia's historic, current and future water temperatures. In each decade since 1960, temperatures in the river have increased between .2 and .4 degrees Celsius due to climate change, or a total of between .5 and 1.5 C, the plan says. The EPA also notes that flow regulation, land use changes, natural variability and other factors also likely influenced the change in temperatures.
Total warming of the lower Columbia River in August since the 1930s is about 2.2 C—rising from about 20 C to about 22 C. "That incorporates all factors, including dam construction in the middle decades and climate change from 1960 to 2000," it says.
The plan also compares warming in the river with and without the existing Columbia and lower Snake River dams since 1970, but including the Columbia River dams in Canada. In August, the lower Columbia River warmed about .4 C per decade with the dams, and would have warmed .26 C per decade without them, it says. In July, it says, the rate of warming is about the same in both conditions, "indicating that the increase in warming since 1970 is primarily attributable to air temperature increases from climate change, and the dams have not exacerbated the warming trend in July," the plan states.
Future increases in temperature—under a mid-range reduction in greenhouse gas emissions—are predicted at .3 C per decade, it says.
The agency predicts that fewer salmon and steelhead will migrate in the lower Columbia River from mid-July through August under warming trends, which will lead to a shift in the timing of migration. "Adult sockeye salmon and summer Chinook will likely continue to migrate earlier as already observed, with very few migrants in July," it says. Adult fall Chinook are likely to migrate later, and those that migrate in August will need to use cold water refuges in order to have sufficient energy to spawn. The warmer water may result in a split migration season, with early summer and late summer runs. "However, whether these species can shift their migration timing to adapt to the rate of warming, and whether such shifts can be done successfully without disruption to their full freshwater life cycle, is uncertain," it says.
The plan also raises concerns over a lack of cold water refuges between the Deschutes River and McNary Dam, including the John Day reservoir, which has the highest temperatures in the lower Columbia. "This nearly 100-mile reach poses the greatest risk from water temperatures for migrating salmon and steelhead," it says. There is little opportunity to restore areas of cold water in this reach, the plan noted, adding that even under natural conditions there were likely only a few small tributaries providing cool water to that section of river.
The tributaries that provide cold water refuges are also predicted to increase in temperature, the plan notes.
The 12 primary tributaries that contribute to cold water refuges include four below Bonneville Dam (Cowlitz River, Lewis River, Sandy River and Tanner Creek); seven between Bonneville and The Dalles dams (Eagle Creek, Wind River, Herman Creek, White Salmon River, Little White Salmon River, Hood River and Klickitat River); and one between The Dalles and John Day dams (Deschutes River).
The Cowlitz, Lewis, Little White Salmon and Deschutes rivers provide the largest cold water refuges.