The issue of fish passage at Mirror Pond has come up again recently…in short, I do not think that a roughened channel or natural type fishway would work at this site. I am not familiar with the site, so I wouldn’t want to say 100%, but typically these types of solutions only work in cases when the obstruction is less than 5 or 6 feet tall. In the case of Mirror Pond Dam, my information says its around 20 feet tall. Generally at such a large obstruction there is not enough space downstream to effectively provide passage with a roughened channel or another type of “natural” solution. For example, NMFS guidelines for a roughened channel is max 150 feet long, and maximum 6% gradient. That means that even at these maximums, which may not provide very good fish passage, the maximum “height” the roughened channel could be is 9 feet. Couple that with the natural channel gradient in the stream, which on the Deschutes is likely 1-3% (which gives you a drop of 1.5 to 4.5 feet over 150’), then the roughened channel would only be overcoming 4.5 to 7.5 feet of the 20 foot barrier. In addition, typically roughened channels become very unstable at heights above 5 or 6 feet.
If and when stakeholders and interested parties go down the road of developing and implementing fish passage at Mirror Pond, we will have all options on the table, and will investigate all possibilities for passage. The ultimate goal will be to develop a project that meets the needs of the native migratory fish on site, and meets the needs of all the stakeholders at the site.
I appreciate your participation, interest, and questions in this matter, and do feel free to let me know if you have any other questions.
Thank you, and take care.
ODFW-Assistant Fish Passage Coordinator
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