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Dam Raising?

Actually, there is absolutely no dam raising happening. This is a change in water levels behind the existing and unchanged Coyote Dam. There is no fish passage around Coyote Dam either. While Mendocino Co. supes are ‘studying’ the feasibility of raising Coyote Dam, today’s PD story isn’t about that.

The changes are regulatory changes:

Right now, the flood control storage operating rule curve for water levels behind Coyote Dam require that the water level does not exceed 737.5′ elevation. This means that under the current rules, there must be water releases in anticipation of storm water inflows until April 1st, so as to not exceed that level with storm water inflows. Since the dam was supposedly built primarily as a flood control structure, the first priority during the rainy season is to have enough capacity to hold significant rainfall back. “reign in the rain runoff”, so to speak.

Under the existing rules, after April 1 the reservoir can be managed for water supply, and the water levels can go up to a maximum of 748′ elevation. In the past, this has been filled with late spring rains, even after the flood control levels are maintained as the maximum height until April 1.

However, Sonoma County Water Agency is noting that in the past few years (10+?), significant spring rains have not materialized to fill this water supply pool. Climate change? So, for instance, last year, the Corps of Engineers discharged some 10,000acre feet of water in late winter, in anticipation of spring storms which never materialized, leaving L. Mendocino water levels significantly low. Hence the foundation for last year’s ‘drought’.

What SCWA wants now (and has been lobbying for in D.C. and elsewhere), and is apparently getting with a very quick change in rules by USACE, is to end the rainy season mandate for 737.5′ elevation on March 1st, a full month earlier than the existing rule. This will hopefully allow March rains to be used to help fill the water supply pool (which would now go up to an elevation of 761.8′, rather than the current 748′ max.).

The expectation is that this will allow more water supply storage space earlier in the season, provide more actual supply storage going into the dry season, and increase the ability to store enough water for fall-run Chinook without the kind of release and diversion restrictions imposed by the state regional water board we saw last year.

One of the issues for the Army Corps, however, is that the campgrounds on the lake are among their most popular sites of any USACE reservoir facility in the west. The higher water levels would flood a bunch of them and perhaps some access roads. USACE is very unhappy about that.

Also, the Redwood Valley Water District, which buys ‘surplus’ water from SCWA’s storage in L. Mendocino, has an inlet pipe that cannot be reached by water when the lake drops significantly, as it did last year. Bad design. So they are very happy with this increase in storage elevation levels.

It will be very interesting to see what happens to the geology in the area: There is apparently a significant increase in earthquakes caused by excess weight of water when the lake is raised higher than the existing summertime 748′ elevation.

As far as fish passage beyond Coyote Dam further up the East Branch Russian River, nothing is changed. The fish either have to grow wings, or make do with what they have. Or sit at the base of the dam and become food for pikeminnow.

FOER continues to advocate that Lake Mendocino fill on its own watershed, and that the PVP diversions cease. Southern Mendocino, Sonoma and Marin will just have to do a better job of using what they’ve got, without depending on the annual bailout of the overappropriated Russian River with Eel River subsidies. Fish passage up to the Potter Valley would be great.

David Keller
FOER