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Bend Bulletin - Fish passage to be considered at Mirror Pond dam

This article was published on: 02/26/22 10:13 AM

Public invited to comment starting this spring

By Brenna Visser

The public soon will have a say in what kind of fish passage should be built at the Mirror Pond dam.

Earlier this month, the Mirror Pond Fish Passage Advisory Committee decided to explore three different kinds of fish passage options at the dam that sits in the middle of the city at Mirror Pond. The committee is a joint effort between the city of Bend and the Bend Park & Recreation District but facilitated by the Central Oregon Intergovernmental Council.
While fish passage has long been a part of community discussions surrounding how to manage Mirror Pond and this stretch of the Deschutes River, momentum to seriously fund and implement a passage came out of an intergovernmental agreement between the city and the park district that was signed in 2019.

Through the spring and summer, engineers will study three different kinds of fish ladder designs: a traditional steel or concrete fish ladder, a rock ramp, and a natural fish byway.
As work moves forward for each option, the main factors that will be considered are safety, aesthetics and the ability to effectively pass fish, said Scott Wright, the project engineer working on the fish passage project.

“Traditionally, the concrete fish ladder has always been a staple,” Wright said. “What has happened in the last 10 years is we’ve figured out the natural conditions similar to the existing river are better for fish passage, so we’ve added a nature like fishway (as an option).”

Here is how the three options would generally work. A traditional fish ladder uses concrete or steel steps for fish to swim over. A rock ramp fish ladder builds up the bed of the river with rocks up and over the dam.

A natural fish bypass uses a smaller channel out of natural river elements like wood and natural gravel to get fish past an obstruction, Wright said.

All of these options have trade-offs, said Vernita Ediger, the consultant who helped facilitate the advisory committee.

While costs of each have yet to be determined, in general, Ediger said a traditional fish ladder can be cheaper than the other options. But it also brings other challenges, such as ongoing maintenance to keep ice off the structure in the winter. They are also not as aesthetically pleasing, she said.

The rock ramp looks more natural, but presents other challenges such as possibly introducing invasive species when bringing in the materials to build it, and possibly being vulnerable to a high water event, Ediger said. A high water event could possibly displace the carefully placed rocks, which could lead to maintenance work in the future.

“You want to make it effective for the fish and also durable and sustainable,” she said.
A natural fish byway also is more aesthetically pleasing and creates a natural channel that directs fish around the dam, but also faces the challenge of having invasive species be introduced when natural materials are brought in to build it. Another factor to consider is whether in low-water times fish will still be able to use it, Ediger said.

“The key thing we are trying to do is make sure fish pass and any of these structures will get that job done,” she said.

The first phase of design is already underway, which hopefully will rule out any option that truly isn’t viable at all, Ediger said. The public will be invited to comment on the designs in the public meeting sometime in May, she said.

The next phase will do more in-depth design work on one option, and the public will be again invited to comment, Ediger said.

The advisory committee will then make a recommendation to the park board and the Bend City Council. A decision made by each public body isn’t anticipated until early fall, said Don Horton, the executive director of the park district.