Wednesday, February 25, 2009

Lake Mendocino

A more recent photo of Lake Mendocino

So, you think that this is a drought year, this is what it was like when I was a kid. Lake Mendocino looking south.

This is Coyote Valley, when Lake Mendocino was first filed we called it "Coyote Lake". It is now known as Lake Mendocino. We had friends that had a summer home in Clear Lake Oaks and we would quite frequently drive through the valley on what was known as the "Coyote Cut-off".

Coyote Lake today. (looking west)


ross sherburn said...

my dad and several other local folks called the lake a big mud hole,when they first filled it!!!guess they figured round valley would have had more capacity???

Ben said...

Looks like they finally got some water. Ours, of course.

Robin Shelley said...

I've read recently that Lake Mendo is at its lowest level in 20 years right now & the lowest it has ever been in FEB.
If I'm not mistaken, Sonoma Co. owns most of the water rights to this reservoir... a stupid decision that has been the source of bitter argument & regret for many years.

Anonymous said...

Good posts Ernie, keep it coming. Without Eko, you've been carrying the team.

Kristabel said...

Ernie, I always learn so much from you!

I have fond memories of stargazing for hours with my dad at Lake Mendocino when I was a kid.

Ernie Branscomb said...

Coyote Dam and lake Mendocino was completed in 1959. The Dam holds 118,000 Acre Feet of water.

Some more on:

The Potter Valley Project
Part 1: Eel-Russian Flows
by Roger Dixon,
The Upper Eel Coalition
There has been much written about the recent controversy on the Eel River; some of it accurate and informative, and some not. In this series of articles I will try to give you, kind reader, as many facts as you can stand. Some writers are most interested in presenting information so as to justify an agenda. For example, the Pacific Gas and Electric Company's (PG&E) Potter Valley Project (PVP) makes money by spinning its hydroelectric turbines. The more Eel River water it diverts through its powerhouse, the more money it makes. Therefore, every statement PG&E makes about flows in the Eel and the Russian is intended to convince the reader that PG&E should be allowed to divert a maximum amount of Eel River water. By the same token, some businesses in Sonoma County, (agricultural, recreational, real estate), make hundreds of millions of dollars every year by using water from the Eel diversion.

The Basics

Skip this part if you already know about acre-feet, cfs, Mg/d, etc. The most common units of measure when talking about rivers and water systems are the acre-foot (ac-ft) and Cubic Feet Per Second (cfs). You would use acre-feet to describe how much water is in a reservoir or how much water you diverted in a year. An acre-foot is the volume of water it takes to flood one acre of land one foot deep. It is equal to 43,000 cubic feet (cf) or 322,500 gallons. A Cubic Foot Per Second is how we measure how much water is flowing past a given point on a river, stream, or canal. It just so happens that a flow of one cfs for one day equals about two ac-ft (actually 1 cfs/day=1.983 ac-ft). This makes calculations relatively simple. Municipal water systems often measure their water in gallons rather than cubic feet. This can confuse things, so just remember that [one gallon=.13 cf] and [1,000,000 gal=3 ac-ft].

The System

The PVP is made up of three main components. The first, starting from the headwaters, is Scott Dam which creates Lake Pillsbury. The lake receives about 400,000 ac-ft of run off every year. Scott Dam can store about 60,000 ac-ft. Around April first of every year PG&E is permitted to raise its "Flood Gates". These gates, in effect, raise the level of the lake by ten feet which amounts to an additional 20,000 ac-ft and brings the total possible storage in Lake Pillsbury to about 80,000 ac-ft. (I'll discuss these gates in more detail later.) Therefore, the great majority of water entering the lake every year spills out. Scott Dam has no fish ladder and thus is an absolute barrier to salmon and steelhead, thereby eliminating over one hundred miles of habitat. This problem has never been addressed. Water is released from the lake through what is called the "needle valve" which can release a maximum of about 350 cfs. The needle valve taps the reservoir near its bottom and ejects it in a plume to help oxygenate the water. When the lake is full, water can also be released by partially opening the flood gates.

The next component downstream is Capehorn Dam which creates VanArsdale Reservoir. It is not really a reservoir anymore because it is nearly full of silt and gravel. It only functions as a check dam to maintain the needed elevation so that the "diversion" can operate. In the summer, PG&E places "flash boards" on top of Capehorn Dam to raise the level four feet. This allows the reservoir to act as a buffer to changes in flows. There is a fish ladder on Capehorn Dam that works under some conditions but not others. This ladder allows most salmon and steelhead to access the habitat between the two dams.

The last component is the diversion. This is the tunnel that carries water from VanArsdale Reservoir through the mountain and delivers it to PG&E's power plant in Potter Valley. The tunnel has a maximum capacity of about 350 cfs and a head, (drop in elevation), of about 400 feet. It diverts, on average, about 160,000 ac-ft of Eel River water into the Russian River system every year. The now famous fish screen is intended to prevent any more little fish from being killed in this tunnel or the power plant. Once the Eel River water leaves the power plant, at the "tailrace", it is legally abandoned. Neither PG&E nor anyone else has any consumptive rights to Eel River water. Now the situation gets a little more complicated. Even though the PVP ends at the tailrace, many people downstream use the diverted Eel River water. So we must understand also the operation of the Russian River Basin Project (RRBP).

The RRBP has two main components; Coyote Dam/Lake Mendocino and Warm Springs Dam/Lake Sonoma. Of the 160,000 ac-ft diverted from the Eel, 20,000 ac-ft gets used by Potter Valley and the remainder, 140,000 ac-ft enters Lake Mendocino. In addition, the natural watershed above Lake Mendocino contributes about 110,000 ac-ft every year. So the total amount entering Lake Mendocino every year is about 250,000 ac-ft. (Actually it is a little more because some of Potter Valley's 20,000 ac-ft runs off and also ends up in Lake Mendocino. This level of detail will be ignored for now.)

Lake Mendocino can only safely store about 88,000 ac-ft, which means that almost every year most of the water entering Lake Mendocino spills out during the winter high flows. Lake Sonoma gets its supply from its own watershed only and receives about 156,000 ac-ft each year. It can store about 245,000 ac-ft, which is more than comes in every year. Therefore, Lake Sonoma rarely spills except during wet winters like 1994-95. All of the above discussions ignore the flood control aspects of the reservoirs which have another set of numbers entirely.

Water Use

Many statements have been made by interested parties who claim to be "dependent" on the continued diversion of Eel River water. They claim that they will suffer without it and that there are no alternative sources of water. Here we will take a close look at this "dependence".

Potter Valley uses about 20,000 ac-ft of Eel River water every year. They have a shallow fractured aquifer that will not hold water during dry spells, so pumping from wells is not practical. They have no good sites for reservoirs, so they can't store winter run off. Very few people, if anyone, would argue with Potter Valley's claim to be genuinely dependent on diversions of Eel River water. Fortunately for them, they were the only group of water users prudent enough to sign a contract which obligates PG&E to deliver the water.

The next group of water users are the agricultural and municipal users in Mendocino County. They use water either directly from the lake or they pump from the river below it. Basically, this is everyone on the Russian River except Potter Valley. A recent survey by the Mendocino County Water Agency showed that they use about 13,000 ac-ft. A report by Gary Akerstrum of the "Flood Control District" showed they use 17,000 ac-ft. A report by Tom Johnson of the "District" indicated they used about 23,000 ac-ft. Since they can't agree, we will compromise and say that 17,000 ac-ft is all the water that is needed from Lake Mendocino. Since we have seen that the lake gets 110,000 ac-ft from its own watershed it is clear that there is more than enough water within the county, without the diversion, to meet all the county's needs. For now we will not try to answer the question "Does Mendocino County have rights to the water within its borders?". That is a very complicated issue. Suffice for now to say that Mendocino's rights to Russian River water are in many cases superior to Sonoma's rights. Another complication is that not all the water in Lake Mendocino can be used for people. A large chunk is used to maintain minimum flows in the Russian below Coyote Dam. In a normal water-year about 150 cfs is continuously released into the Russian primarily for the recreational benefits. This can add up to as much as 80,000 ac-ft. Once thought to benefit the fishery, these unnaturally high flows are now recognized as a detriment because they provide excellent habitat for predator fish like Bass and P. Grandis (commonly called Squawfish). In the event of the loss of Eel River water this minimum of 150 cfs would automatically be reduced, by regulation, to 25 cfs or the equivalent of 14,000 ac-ft annually. This is a savings of 66,000 ac-ft. It is easy to see that Mendocino County, viewed unilaterally, has no need whatsoever for Eel River water. It only looks like they need it because of Sonoma County's involvement in this complicated water sharing arrangement.

The last group of water users are those in Sonoma County who use the Russian River, (which is partly Eel water), for agriculture, domestic use, and recreation. The amount of consumption is difficult to quantify. Johnson's report claims they use about 50,000 ac-ft while Akerstrum says they use about 80,000 ac-ft. In any event it is a lot more than is used in Mendocino County and more than can be supplied by the Lake Mendocino watershed alone. It appears that Sonoma County needs the continuation of the Eel River diversion, and that their claim of dependence is genuine. And it would be true, were it not for the supply available in Lake Sonoma.

In 1990 an analysis was prepared, in part, to determine the impacts on Sonoma County if the Eel diversion were lost. The conclusion then was that the impacts would be minimal, "it is the scenario which would be the easiest to rectify", because of the automatic lowering of minimum flows in the Russian mentioned above. Another analysis was prepared in September of 1994 to look at alternatives for Sonoma County if the Potter Valley Project were abandoned by PG&E. One of the options discussed was to run a pipe from Warm Springs Dam north to the county line to supply Sonoma County users with Sonoma County water in lieu of Eel River and/or Mendocino County water. While this option would cost about $40 million, in the long run it is cheaper than what is now being discussed between Sonoma County and PG&E; subsidizing PG&E for $2+ million/year for the next 27 years. This piping of Lake Sonoma option would also insulate Sonoma County from any risks associated with the future of PVP. It is interesting to note that both of these analyses were prepared by Robert Beach, then head of the Sonoma County Water Agency.


This discussion is, of course, very superficial. The Eel-Russian system is complex and dynamic. One doesn't just drain a reservoir dry and then fill it up again; it is not that simple. Water is constantly entering and leaving the system at many different rates. It would be negligent to base specific recommendations for change on this level of analysis. It is also negligent, or worse, to recommend changes based on faulty or biased analysis. The Potter Valley Project in its present state has significant impacts on both the Eel and the Russian Rivers. The Project is now about to be subsidized, sold, or abandoned. Any of these changes will subsequently alter the impacts on both rivers. Now is the time for a careful analysis of how we manage this system before we make any changes. We should not be jumping to conclusions or rushing to judgments. Maintaining the status quo is just as much a rush to judgment as abandoning the PVP would be. We are fortunate that the Eel-Russian system is not in the dire straits of other rivers like the Navarro and the Napa. Those rivers have barely the supply, if that, to meet present demands. I hope this article makes clear that the Eel-Russian system has an abundance of available flows and storage capacity. There is more than enough water in the system to meet all genuine needs. But there will never be enough water for those who would exploit these rivers for profit.

P.S. The "flood gates" on top of Scott Dam is a misnomer. They don't do anything to control or lessen the risk of flood damage. In nineteen years out of twenty, Lake Pillsbury has an uncontrolled spill and the gates do nothing to stop it. In fact when there is the danger of spilling over the top of the gates, PG&E must open them so that they are not damaged by being overtopped. On the other hand, if Lake Pillsbury were full and the dam collapsed, there would be a catastrophic flood with much loss of property and possibly life in the area below Van- Arsdale.

Copyright Mendocino Environmental Center 1995

Donna Schindel said...

Are there any photos of Coyote Valley before they built the dam and flooded it? I can't find anything online!