This article was published on: 05/1/19 12:00 AM
By Ned Dempsey
I am writing about the removal of silt from Mirror Pond. Based on my extensive history and background relating to this type of project, I wanted to express my thoughts and views on the issues as well as on some of the claims that are being used to try to stop the project.
The dam
There continues to be concerns and comments about the future of the dam’s operation and its useful life.
This is a rock crib gravity dam, a design originally developed by the Romans. Some of these Roman-built dams continue to be operational in Europe today. While the Newport dam is 100 years old, it is a design that can last centuries.
The second issue is whether it will continue in operation. The dam produces renewable hydropower and Pacific Power, the owner of the dam, decided to keep and operate the dam indefinitely in 2018.
Silt sources
There continue to be statements that the primary source of silt being deposited in Mirror Pond comes from upstream and riverbank erosion. I disagree because:
1) Actual silt samples taken from the pond do not support this concept.
2) The U.S. Forest Service conducted two bank erosion studies between Benham Falls and Wickiup. I was involved in producing both studies. The studies do not support the claims.
3) Upstream sources are primarily pumice and organic matter. Both are very low density, move with very little current and tend to be carried through the pond.
4) Stormwater from impervious surfaces (streets, parking lots, compacted soil, buildings and roofs) contributes to the silt load. This stormwater silt is higher density, drops out faster and tends to stay in the pond.
Natural stabilized state
Statements have been made that the pond is “approaching” a natural stabilized state.
While this statement is true, I believe it requires context in order to understand what it means. The pond started “approaching” a natural stabilized state the day it went operational and again after the dredging in 1984.
It is what rivers do.
My opinion is that the pond has not stabilized; it is still accumulating silt — especially the heavy fraction of silt from stormwater … and the next step in the process will be vegetation growth.
Creation of wetlands
Many claim the creation of wetland would be a benefit to the river.
While wetlands occur in nature and are part of the ecosystem, they also create impacts that need to be considered.
By definition, wetlands create oxygen-free zones. They will change the ecology of the established system. Wetlands do sequester carbon which creates a benefit, however, they also produce methane and nitrous oxide gases. These gases are greenhouse gases and create approximately 300 times more negative impact on climate change than carbon. As climate change becomes more understood and important, all of the negative unintended consequences need to be considered.
Habitat creation
This project, as a result of being granted a permit, has dedicated funds to create or improve habitat on the Deschutes River. There is no identified habitat being destroyed in the silt removal process.
Natural free-flowing sustainable river
Several individuals have advocated for a natural river.
This is an idea without definition. We have built a city around Mirror Pond. We use water for irrigation, recreation and other projects. The ecosystem around the pond has existed for 100 years. And the dam is not going anywhere.
The pond section of the river will never return to a natural state as long as the above conditions exist.
The pond is part of our history and our culture and is an icon of Bend. The pond’s presence improves the quality of life in Bend. And Drake Park, adjacent to the pond, is one of Bend’s most coveted parks.
We need to remove the silt from the pond now before it changes to something less valuable to the city, the county and the citizens.
Thank you for your consideration of my thoughts and views on the future of Mirror Pond.
— Ned Dempsey lives in Bend.