Claire Corlett

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Mirabel Inflatable Dam and Fish Ladder

Mirabel Inflatable Dam and Fish Ladder


Hi I’m David Manning, a principal
environmental specialist with the Sonoma County Water Agency. I manage our natural
resources programs and what you’re looking at here is Mirabel Inflatable
Dam. It’s a seasonal dam; it’s actually a water-filled, rubber bladder during the
low-flow season of the year. So when the winter flow rains come up and there’s
high flow in the river, what you see behind me is still there it just lies
flush on the stream bed. We inflate it in the Springtime, sometime between April
and June, and it typically stays up until November or December. But it can be
inflated at any time of the year that the Water Agency needs to increase its
ability to deliver water to the 600,000 customers in our service area. We get
about half of the water supply benefit we need during our peak periods of the
year, from the water stored behind this dam. We pump that water into a series of
infiltration ponds that we use to recharge the groundwater. We also use all
the water backed up behind the dam. It sits about 11 feet above the stream bed
and backs water up for nearly three miles upstream. There are a series of
wells upstream from this point that also benefit from having that increased level
of water in the river. It facilitates groundwater pumping upstream. This site
has been the focus of a lot of fisheries monitoring and study over the last 10
years. The dam was first put in place in the late 1970s. Chinook Salmon, Coho
Salmon, and Steelhead were listed under the Endangered Species Act between 1996
and 1999, and the Water Agency began a pretty intensive investigation of the
impacts of this facility on the upstream movement of adult salmon and then the
downstream movement of juvenile salmon and Steelhead as they head out to the
ocean. So we’ve been studying the movement of fish past this site using a
few different techniques: right now, here in the Fall when Chinook Salmon are
migrating upstream and Steelhead and Coho Salmon are beginning
their migration, we have fish ladders on either side of the dam that enable fish
to get past the facility. You’ll see fish trying to jump over the height of the
dam; most are unsuccessful so they need fish ladders to help get them upstream.
We have a video monitoring system on the fish ladders on either side of the dam
that is an underwater camera that takes a time-lapse image 24 hours a day, 7 days
a week. We have a staff of biologists and technicians that watch those videos and
count physically the number of fish that move upstream past this site. We see in
terms of the Chinook Salmon, in the past 10 years we’ve been doing this
monitoring, between about twelve hundred and six thousand fish pass upstream
during the time that we have the dam in place. The migration extends beyond the
period that we have the dam inflated because river flow comes up, we no longer
need the dam and we deflate it but fish are still moving upstream past this site.
That’s particularly true for the Steelhead. Most of them return to the
river in December, January, February, and March. At that time the dam is down so
this count that we get is largely based on Chinook Salmon, the first of the fish
returning to the river. So this entire facility is critical to our water supply
and we’re very concerned about the environmental impacts. It’s been reviewed
extensively by the National Marine Fisheries Service, the California
Department of Fish and Game, and our own biological research and monitoring over
the last ten years. And we’ve been able to demonstrate that we can have our
water supply safely meet the needs of fish as they pass by this facility. A
couple of enhancements and improvements will make that even better, but this site
is an incredibly valuable resource for us to gauge the number of fish that move
upstream in the Russian River and down stream every year, and we’re very pleased
that it doesn’t impact or preclude the migration of fish up and down the
Russian River.

2 comments on “Mirabel Inflatable Dam and Fish Ladder

  1. That's soft engineering weir done very well; it's function is clear and the approach to groundwater recharge has me feeling enthusiastic rather than hopeful. The fish ladders themselves are still mysterious. Was this system installed in 2000? Especialy when that that is the case I would plead for top-up funding to try a drastic riparian vegetation pruning and see if recruitment can be upregulated and get you back to 2003 levels in a few years. I'd love to know more. Best regards,

  2. Nice Video..I liked..I also did a You tube Video on the Herring run fish ladder..You might like that I took my Go Pro and got some underwater shot..Check it out if you can..https://www.youtube.com/watch?v=48bHhWK4auw..If you like please sub..Trying to get over 1000 Subs

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