Response from ODFW on fish passage at Mirror Pond

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.
Ken Loffink
ODFW-Assistant Fish Passage Coordinator

The Reply to: question-to-odfw-on-natural-type-fishways

Response from ODFW on fish passage at Mirror Pond

verticalslot1My apologies for not getting back to you on your request sooner. I have attached examples of fish passage facilities that have been used at sites similar to the Mirror Pond site. The first two pictures are of “vertical slot” fishways, which would be my first choice given the fish species and hydrology in the Deschutes at that site. This style of fishway allows fish to “swim through” rather than jump over each step of the ladder, and tends to perform well on larger river systems. For a dam structure that is 13-15 feet tall I would expect a vertical slot with at least 17 to 30 steps.

The second two pictures are of pool and weir fishways, which require fish to leap over each step. These pass fish rather well, especially in low water situations but require a little more maintenance versus the vertical slot because the “weirs” need to be adjusted as the river flows go up and down. Vertical slots are self adjusting. Given fish species in the Deschutes the max “jump height” at each step would be 6 inches, therefore a pool and weir solution would have anywhere from 26-30 steps to provide adequate passage over the dam at Mirror Pond.

That is just some basic information and assumptions on possible fish passage solutions, and when the time comes for passage the site will be thoroughly poured over to ensure the correct solution is selected to provide fish passage. If you have any questions, please let me know.

Thank you for your interest and community involvement, take care.

Ken Loffink
Assistant Fish Passage Coordinator
Oregon Department of Fish and Wildlife

vertical slot

Middle Falls- Middle Creek 12

Morgan Creek STEP 3