Yes, you read that right. The lower Deschutes River is now running colder. This is due to a change in Portland General Electric and Confederated Tribes of Warm Springs temperature and flow management at the Pelton-Round Butte Dam Complex.
Sources at PGE state the new temperature (which is now running at about 55 to 56 degrees at the outflow of the Pelton Re-regulation Dam) is the result of increasing the bottom draw component of the bottom-surface water mix at the Selective Water Withdrawal (SWW) Tower at Round Butte Dam. The bottom draw is now 45% of the blend being discharged.
We have learned that this is being done as part of a feasibility study to determine if there is enough cold water stored at the bottom of the reservoir to support decreasing the previous temperatures being created at the SWW Tower.
Hopefully this cold water release becomes more than a feasibility study. The immediate impact on the river is obvious. The temperature was decreased with the new blend starting the day before the Deschutes River Alliance initiated two weeks of continuous water quality monitoring based on our 2014 Science Work Plan and Investigation. The change in water quality has been immediate. Turbidity especially has improved, but so have other parameters.
Increased use of bottom draw water might also be diluting the nutrient load present in surface water, and the new blend certainly should carry less algae. It is too early in the process, and too late in the algae growing season, to see if this will improve the algae situation in the lower river.
We had several meetings regarding temperature regulation with PGE in 2013. At the time, PGE was fairly intransigent in regard to changing temperature management. We are delighted to see an increased level of flexibility in evaluating management of the dams to benefit the health of the lower Deschutes River.
The DRA will be advocating for maintaining this new temperature management regime. We will also be continuing our research into other water quality parameters that have changed as a consequence of the use of reservoir surface water in dam discharge, as well as the biologic consequences of reservoir surface water withdrawal.
This is good news but there remains much to investigate and understand to ensure that the water quality parameters of all water entering the lower Deschutes promotes a healthy river ecology.
Thanks for your interest and support.
Director of Science and Conservation