When it comes to temperature management at the Pelton-Round Butte three-dam complex (aka the Project) via the Selective Withdrawal (SWW) Tower, a couple similar claims are often made by Project operators in order to justify the current temperature management scheme:
They must save cold water for fall release to benefit Fall Chinook
They will run out of cold water if more bottom water is released earlier in the year
A thorough look at the facts on the ground make it clear that these claims are simply false. Temperature data does not show that cold water will run out or that Fall Chinook have benefitted. On the contrary, current operations cause overall harm to the entire lower Deschutes ecosystem and affects many species. It’s time for the dam Operators, and the Department of Environmental Quality, to take these impacts (along with the unprecedented number of water quality violations) seriously and use the abundant cool, clean bottom water to provide relief to the lower Deschutes River when it’s needed most. This can be done while maintaining their fish passage program and power generation.
Post vs. Pre-Tower Water Releases
Prior to SWW Tower operations, all water released from Lake Billy Chinook was sourced from the hypolimnion, or bottom of the reservoir. The outlet was located at 246 feet below the surface. As is often mentioned by the DRA, this water was cool, clean, and primarily sourced from the Metolius River (Eilers & Vache 2021).
After the SWW Tower started operating in December 2009, water can still be released from the bottom of the reservoir at the same 246-foot depth, but there is also now a surface withdrawal outlet located in the warm epilimnion (top layer of the reservoir) at 39 feet below the surface. Surface water is released in hopes of creating a surface current to attract out-migrating juvenile salmonids to the Tower collection facility. Importantly, in the original Water Quality Monitoring and Management Plan (WQMMP), which is part of the Clean Water Act § 401 Certification Conditions of the current operating license of the project, 100% bottom water release was included in the original Tower blends. However, due to an unspecified operational limitation of the SWW Tower, it can only release a maximum of 60% water from the bottom of the reservoir (PGE 2023). This is an important detail when considering the false temperature management claims made by Project operators, as we describe below.
Running out of Cold Water?
The statement that they will “run out of cold water” is very misleading and misrepresents what actually happens under current operations. A comprehensive water quality study of the Project and lower Deschutes funded by PGE (Eilers & Vache 2021) analyzed the temperature profile in Round Butte Forebay where the SWW Tower on Lake Billy Chinook is located (where water is discharged from the reservoir). This study did, in fact, find that, following Tower operations the forebay holds more cold water in the deeper portion of the reservoir during mid-summer months. Water temperature in the reservoir’s hypolimnetic (deepest) layer is colder after SWW operations started in late 2009. Note the darker blue color indicating colder temperatures at the deeper portion of the bottom thermograph (from 2016, post-Tower) relative to the top thermograph (from 2006, pre-Tower) in the two graphs below. This is intentional on the part of Project operators and is, in part, what they mean by “saving colder water” (PGE 2023).
Vertical water temperature profiles in LBC immediately upstream from the dam as measured in 2006 (top) and 2016 (bottom) (from Eilers & Vache, 2021)
However, it is important to point out that, as noted above, under the current conditions even when maximum bottom water is released, bottom water must be mixed with at least 40% surface water, which is warmer whenever Lake Billy Chinook is thermally stratified. Typically, this stratification occurs mid-March to September (Eilers & Vache 2021, PGE 2023). Therefore, when the bottom water is now mixed with warm surface water, the water released into the lower Deschutes River is actually warmer during the summer months than it was when 100% bottom water was released (see table below), and the little cooling relative to pre-Tower conditions in the fall is disproportionate to this warming. Therefore, the claim of “running out of cold water” is very misleading and simply not true.
Table comparing the theoretical temperatures of water released into the lower Deschutes in 2006 (pre-Tower) and 2016 (post-Tower) based on thermographs above from Eilers & Vache 2021 report. Assumes maximum bottom draw (60%) during the months of June-November in 2016. In actuality, less than 60% bottom draw occurs for much of the summer but this is a simplification to show how operational changes have affected temperature in the lower Deschutes.
Furthermore, violations of the temperature standards set in the lower Deschutes to protect aquatic life (principally spawning salmonids) have increased following Tower operations. The bar graph below clearly shows that while violations of the lower Deschutes temperature standards did occur prior to Tower operations (0-5 days annually), the number days in violation of temperatures standards increased substantially following Tower operations (2-36 days annually). As has been frequently pointed out by the DRA, this is representative of the overall warming trend post-Tower operations, which has contributed to the well-documented negative ecological shifts that have occurred following Tower operations.
Bar graph depicting the number of days in violation of the applicable temperature standards (as of 2023) in the lower Deschutes by year. Temperature data analyzed from the available data record 1980-2022 at the USGS Madras gauge -13 years before SWW Tower operations (1980-1988, 2006-2009) and 13 years following Tower operations (2010-2022).
*Note that during the years 1981-1988, some days of temperature data are missing. Total days of temperature data from this period ranges from 274 to 353 total calendar days per year. Only one year (1988) had less than 300 days of temperature data. The missing data is not believed to skew overall temperature trends.
Need to Save Cold Water for Release in the Fall?
What justification do Project operators give for “saving cold water” for fall release? Operators and supporters of the current temperature management regime claim that current temperature conditions are more “natural” and better for fish in the lower Deschutes; typically Fall Chinook are the focus. In a Q&A from July 21, 2021 posted on PGE’s Deschutes Updates page, which followed warm summer lower Deschutes temperatures, biological services manager Megan Hill, when asked why the SWW operates the way it does responded with:
“Releasing water that matches the calculated WPT [without project temperature] results in more natural seasonal temperature patterns in the lower river. These are temperatures the native Deschutes River fish depend on. This approach ensures that spring temperatures are conducive to fall Chinook growth and helps us save cooler water for the fall when these fish return to spawn” (PGE 2021).
As covered in our recent blog posts on warmer temperatures, dissolved oxygen, pH, and nutrients in the lower River, warmer temperatures and overall decline in water quality have caused negative ecological shifts in the lower Deschutes ecosystem. Temperature is only one component of the water quality considerations that should be taken into account. The DRA contends that the well-documented negative ecological shifts indicate that operational changes following implementation of the SWW Tower have caused overall harm. However, rather than taking a wholistic approach to operational effects on the ecosystem, Project operators generally focus on Fall Chinook as the fish that supposedly benefits that the shifted temperature regime.
The claimed benefits to juvenile Fall Chinook are largely speculative and the data to support increased Fall Chinook growth is not definitive. While Project operators claim that the warmer spring temperatures are “conducive to fall Chinook growth,” a temperature study (Huntington 1999) found no significant difference in emergence timing anywhere in the Deschutes caused by temperature changes from historic operation of the Project relative to pre-dam conditions. Therefore, it is likely that juvenile fall Chinook emergence (and likely subsequent juvenile growth) was not different after the dams were put in place., Therefore, there is little support for the claim that the warmer temperatures in the spring and early summer help juvenile Chinook by earlier emergence or increased growth.
Fall Chinook return numbers in the lower Deschutes do not support the claim of any benefit to Fall Chinook from an effort to “save cold water” for fall release. A thorough analysis conducted by the DRA of Fall Chinook return data, adjusted for whether fish were present as juveniles during SWW operations prior to outmigration, indicated that post-Tower years 2013 – 2021* were not significantly different when compared to the previous 36 return years 1977-2012. Interestingly, comparing these same two time periods (see graphs below), Fall Chinook showed a positive trend (overall increase, top graph) in the pre-Tower years and a negative trend (decline, bottom graph) in the post-Tower years through 2021.
*Note that jacks were not included to simplify this analysis, so 2013 was the first return year where all returning adults would have spent their freshwater residency in the Deschutes after Tower operations
Estimated adult fall Chinook return to mouth of the Deschutes pre-Tower, 1977-2012. Data source: ODFW
Estimated adult fall Chinook return to the mouth of the Deschutes post-Tower, 2013-2021. Data source: ODFW
While the change in trends depicted in the graphs above are not significantly different due to small post-Tower sample size and large variability in both data sets, at the very least the above results suggest that water temperature manipulation (i.e., saving cold water for fall release to convey some benefit to Fall Chinook) is not effective at increasing the adult population post- Tower. More years of post-Tower data are needed to make any confident conclusions about the overall effect Tower operations have on Fall Chinook, and it should be noted that the Tower is only one component that effect the life history of salmonids in the lower Deschutes. Given this, project operators should not be making claims about supposed benefits without data and analysis to back up those claims.
Conclusion
Is there any scientific evidence that Lake Billy Chinook will run out of cold bottom water with more bottom water release or that saving cold water is a benefit to salmon?
No!
The data (much of it collected by PGE) does not show that cold water will run out or that salmon have benefitted. On the contrary, well documented negative outcomes including declines in sensitive aquatic insects, increases in algae and diatoms, increases worms and snails that are intermediate hosts for several fish diseases, and seasonally abundant smallmouth bass suggest that Tower operation has caused overall harm to the Deschutes ecosystem. Furthermore, there is no proof that “saving cold water for fall chinook” results in increased adult returns.
It’s time for the dam Operators and the Department of Environmental Quality to take these impacts, along with the unprecedented number of water quality violations, seriously and use the abundant cool, clean bottom water to provide relief to the lower Deschutes River while not harming their fish passage program or power generation.
