By Keith Vandervere
A cherry red sun behind a veil of smoke. Ash drifting down in tiny gray flakes. For most of September and October, those were the conditions on the Monterey Peninsula every time the wind blew out of the south. The Ventana Wilderness was burning and, with it, much of the Carmel River watershed above the Los Padres Dam.
Although in many years the Carmel River is hardly big enough to qualify as a creek, the Monterey Peninsula depends heavily on its water. Long-time residents know just how unreliable a source it can be. Between the water the steelhead and other fish need to survive, the water the riparian property owners claim title to, and the water drawn off by the municipal water system, there is frequently less than enough to go around. Reading the dusty studies on the succession of new dams proposed over the years, the magnitude of the problem becomes clear. Like squeezing blood from a turnip, squeezing enough water from the Carmel River to satisfy all claimants is a problem that remains unsolved. No feasible dam has ever been designed capable of preventing rationing during the, all too predictable, multi-year droughts.
With a water supply this tenuous, any damage to the watershed would cause concern, but nothing attracts attention quite like a fire. After all, it is the vegetation, the brush and trees, that hold the steep slopes together. Take away the plants and winter rains send the mountainsides running down the canyons in a muddy paste. One result is obvious. More acre feet of storage behind the current Los Padres Dam lost to siltation. Another result is less obvious. Although the proposed Carmel River Dam remains unbuilt, it too loses capacity to siltation.
"The amount of silt we'll see this winter depends on four things," says Henrietta Stern, of the Monterey Peninsula Water Management District. "How much of the watershed burned, how intensely it burned, exactly where it burned, and the severity of the storms we get."
"Of the 26,000 acres of watershed upstream of the Los Padres dam about 16,000 appear to have been affected by the fire," says Marc Lucca, Project Manager for California-American Water Company's embattled Carmel River Dam proposal. "The good news is that around three quarters of the acres affected appear to have burned at low intensity. This is nothing like Marble Cone."
The Marble Cone fire, in the summer of 1977, burned the Ventana Wilderness virtually end to end. Burning in a drought year, with an enormous amount of accumulated fuel, it left large tracts almost completely barren.
"Marble Cone," say Darby Fuerst, General Manager of the Monterey Peninsula Water Management District, "is our worst case scenario. The Marble Cone Fire was very intense and it was followed by a big winter. The Los Padres Dam lost about 550 acre feet of storage to silt in 1978."
1978 was bad, but was it really a worst case scenario? Peak flow in 1978 was 7,030 cubic feet per second (cfs). This is a lot of water, but it is still less than half the 16,000cfs flow of March, 1995, which is itself less than half the "Probable Maximum Flood" of 35,000cfs. Had higher peak flows occurred in 1978, even more silt would have entered the reservoir.
"Siltation after a fire can be an extremely serious problem," says Steve Davis, a Fire Prevention Officer with the US Forest Service. "A dam near Santa Barbara lost nearly 50% of its capacity when a big winter followed a fire."
Experiences like that one, underline just how important the issue of siltation is; not just for the current dam, but for the proposed dam as well. A dam can only provide the amount of water it is designed to as long as its "active storage," the amount of water it is supposed to be able to store and release, is not reduced by siltation. In the planning of the proposed new dam for the Carmel River, the Water District has used the average rate of siltation since the building of the Los Padres Dam, in 1949, as a benchmark, rather than making an allowance for the possibility that worse years than 1978 could occur.
"We figure that 5 to 10 acre feet are lost to siltation at Los Padres Dam in a normal year," says Fuerst. "When you add in the big years, like 1978, you get an overall average of about 30 acre feet lost per year."
These figures are based on the fact that the Los Padres Dam, which had 3,033 acre feet of storage when it was built, today has only about 1,569. By next spring, that number will be even lower, but how much lower, no one can say. The must important of Stern's four factors, the severity of the coming winter storms, cannot be predicted.
"People realize that the Los Padres and San Clemente dams are unable to hold the amount of water they were designed to store because of siltation," says Gillian Taylor, Chair of the Ventana Chapter of the Sierra Club. "They worry, and with good reason, that they will be stuck with the bill for an expensive new dam, only to see the same thing happen to it."
"The new dam would set aside 2,000 acre feet for siltation. That's enough space to last 70 to 100 years," says Stern, echoing the words of the Environmental Impact Report.
The proposed dam is supposed to hold 24,000 acre feet of water. With 2,000 acre feet set aside for siltation, 22,000 acre feet are left for "active storage." This 22,000 acre feet is the capacity which all the voluminous studies assume the dam will have available. It is the dam's ability to store 22,000 acre feet of water which would allow it to perform as advertised. Even a small reduction in that capacity would compromise the dam's ability to provide as much water as it should, when it should.
"At 30 acre feet per year, 2,000 acre feet would fill up in 67 years, not 70 to 100 years," says engineer, John Brennan, of the anti-dam, Citizens for Alternative Water Solutions. "But that's not the point. The point is that the 2,000 acre feet of silt storage is an illusion in the first place. Before it is even built, the new dam will have lost storage capacity."
"The 2,000 acre foot figure refers to the amount of water below the level of the outlet works," explains Fuerst. "There will be no way to drain the bottom 2,000 acre feet of the reservoir. It's dead storage. That 2,000 acre feet can silt in without affecting the performance of the dam."
"That would be fine if the silt all went into the deep pool against the dam, like they want it to," says Brennan. "Unfortunately, that's not the way things work. Most of the sediment load settles out as soon as the water slows down. Look at the current Los Padres Dam. It isn't the pool against the dam that's filled in, it's the back of the reservoir."
The proposed dam would be built downstream of the current Los Padres Dam. The current dam and its reservoir would be buried under the reservoir of the new dam. "Every acre foot of silt that washes into the Los Padres Dam today is also an acre foot being taken directly out of the theoretical 22,000 acre foot active capacity of the proposed dam," says Brennan. "The reservoir behind the current dam is part of the reservoir that would back up behind the proposed dam."
The 24,000 acre foot capacity of the proposed dam was calculated based on 1984 figures that assumed the current Los Padres Dam had a capacity of 2,179 acre feet. Around 610 acre feet have been lost since then. Even if, in spite of this years fire, the rate of siltation over the next several years averages out at around 30 acre feet per year, about 800 acre feet will have been lost by the earliest a new dam could possibly be built; perhaps in 2006. The new dam would be unable to provide as much storage as anticipated from its very first day. This situation would grow worse with each passing year, although at a slower rate as some of the sediment found its way into the 2,000 acre feet of dead storage.
"There is no plan to dredge or otherwise remove sediment from the current dam, should the new dam be constructed," concedes Fuerst. "Any problem of loss of active capacity would have to be dealt with in the final design stage."
"The Water District is in a bind on this one," says Taylor. "In their effort to justify a new dam they have dismissed dredging as completely infeasible, yet now, unless they dredge, their new dam won't be able to perform as promised from the day it's built. Dredging, if it happens, will come as just one more expensive surprise to the ratepayers and they won't find out about it until long after permission has been granted to build the dam and all the permits are in hand. Unfortunately, the dam proposal is full of unpleasant surprises like this. Expensive items that aren't being counted when the official cost estimates are printed up."
Environmental Impact Reports prepared for the Water District have set the cost of removing 854 acre feet of sediment from the Los Padres Dam at somewhere between 11 and 40 million (1996) dollars, not counting mitigation costs, "which could be substantial."If these figures are even in the ballpark, it is unlikely that any dredging will ever occur."
The Water District should be honest," says Brennan. "They should subtract the 800 to 1,000 acre feet they'll already have lost, before a dam is built, from their active storage figure. Then they should calculate the rate at which siltation will occur outside of their dead storage pool and subtract enough acre feet to accommodate that infill over the 70 to 100 years they want to claim the dam will operate correctly. Once they come up with a more realistic active storage figure, they should redo their analysis of how the dam will perform based on that figure. They don't want to do that, of course, because it would reveal that the dam is an even worse deal than it looks like now. Less drought protection, even harder on the fish and plants, less water for everyone."
"I hope the attention focused on the siltation issue by these fires will finally explode the myth that the proposed dam can go 70 to 100 years before its active storage is compromised by siltation," says Taylor.
A bigger question may be whether a population as large as the Monterey Peninsula's can afford to continue focusing its water supply planning on such a fragile source of water.
* Published in the 3 December 1999 issue of "News From Home" ©1999 Carmel Publishing Company
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