How will Deschutes River temperatures change?
January 28th, 2009
A fishing guide asked whether the river water downstream of the underwater tower (officially known as the Selective Water Withdrawal tower) would become warmer or cooler when the fish passage system is operational. Here’s my answer:
Once the underwater tower is built and operational, it will likely take a year or so for the temperatures in Lake Billy Chinook to stabilize. Computer modeling has shown that the temperatures in the Deschutes River below the Pelton-Round Butte Project will increase or decrease, depending on the time of year.
The modeling shows:
• December and January temperatures will see relatively little or no change.
• February through July temperatures will increase between 0 to 2 degrees Celsius (0 to nearly 4 degrees Fahrenheit).
• August will see relatively no change.
• September through November temperatures will be lower by 0 to 1.5 degrees Celsius (0 to almost 2 degrees Fahrenheit).
These changes will bring the lower river temperatures to at or below pre-dam conditions. Bringing river temperatures back to pre-dam conditions is required under our federal operating license.
It’s important to note that these temperatures are projected for the Madras gage, just downstream of the Pelton Reregulating dam, which measures river temperature, flow and elevation. I’m not sure how the temperature changes translate downstream, or if the modeling extended downstream beyond the Madras gage. In my opinion, it seems logical that the minor temperature changes will be even less dramatic the farther downstream from the project.
