Capitol Journal: California’s reservoirs are filled with gunk, and it’s crowding out room to store water


Let’s say you owned a four-bedroom house, but one room was useless because of clutter. You’d probably eventually take a deep breath and clear out the crap.

You’d reclaim the room.

That’s pretty much the situation with many reservoirs in California. They’ve got too much gunk in them. And it’s crowding out space for water storage.

But you don’t hear any deep breaths being taken in Sacramento. There’s no serious thought of removing the junk — silt, sand, gravel — and making more room for storm runoff.


Instead, you hear demands for more dams and replenishing of groundwater.

A dam or two probably makes sense, depending on location and who pays.

Aquifers certainly need to be recharged, especially in the dry San Joaquin Valley. There, over-pumping of groundwater for agriculture has caused the land to sink dangerously in some areas.

You also hear a lot about other smart solutions: capturing storm water, recycling, conservation and desalination. But there’s hardly any talk about cleaning up and improving use of existing reservoirs.

Former state Sen. Fran Pavley (D-Agoura Hills), who focused in Sacramento on climate change, water and the environment, reminded me of this in a recent email. I’d just written a column pointing out that California already has lots of dams — 1,400-plus — and used up almost all the practical places to build more.

“I tried several times to incorporate into the state budget or the [2014] water bond money to clean up the silt in our existing reservoirs,” she wrote. “We could increase our reservoir capacity if we dredged out the silt.”

I phoned her. “I knew full well taking out silt would be quicker and less expensive than building a new storage reservoir,” she said. “But the priority was to build more dams.”


In 2014, Pavley sponsored a bill to require the state to study the worst silted-up dams. The goal was to find out how much storage was being lost and estimate the cost of hauling off the sediment. The measure was killed in an Assembly committee.

The Brown administration estimated the study would cost $100,000 to $500,000 per dam. Examining just 5% of the reservoirs would run between $6 million and $30 million, it figured.

That’s a drop in the bucket compared to most water planning costs.

Nothing about California water, of course, is simple.

There’s much skepticism about whether it makes economic sense to attempt to remove silt from lots of reservoirs.

“The ultimate fate of every dam is to fill with sediment, but that’s like saying in the long run we’ll all be dead,” says Jay Lund, director of the UC Davis Center for Watershed Sciences.

If the goal is to increase water storage, Lund has calculated it would be less expensive to raise the height of some major dams such as Shasta and San Luis.

When reservoirs are dredged, he adds, “you have to find some place to put the silt. Reservoirs are up in the hills. There aren’t a lot of flat places to put it.


“Ever pick up a cubic yard of sediment dredged out of a reservoir? It’s heavy,” Lund says. “Gravel, sand, mud. Take it down to a city where they maybe can use it and all the neighbors along the road are going to have a problem. There’s wear and tear on the roads.”

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But silting of reservoirs will only get worse unless some genius comes up with a solution.

“It’s never going to get better,” says Jeffrey Mount, a water expert at the Public Policy Institute of California. “We know how this ends. All reservoirs are destined to fill up with sediment or fall down or be taken down.

“All are losing some fraction of capacity. That’s a universal truth. It’s happening around the world. It’s a global engineering challenge.”

But all reservoirs aren’t the same. It’s generally agreed that the big dams on the west slope of the Sierra have less of a silt problem than smaller reservoirs in the Coast Range. That’s because Sierra streams tumble over firm granite, unlike coastal waterways that roll over mushier ground.

A 2009 report by UC Berkeley professors G. Matt Kondolf and Toby Minear estimated that 4.5% of California’s total reservoir space had been clogged by sediment. That would represent around 1.8 million acre-feet of lost water storage — about the same size as the big dams being proposed.


But it’s much worse in many small reservoirs. The professors estimated that more than 120 reservoirs had less than 25% of their original capacity remaining. And nearly 190 had lost more than 50% of their water space.

The problem goes beyond loss of water storage capacity. Before the dams, much of that sediment rolled down rivers and was spread along California beaches. Many now are starving for sand.

Also, the sediment provided spawning beds for steelhead trout, which have practically disappeared from our dammed coastal streams.

One poster child for sedimentation is Matilija Dam near Ojai. Built in 1947, it killed off steelhead runs in the Ventura River and gradually filled with crud. Local groups for years have been searching for the $80 million to tear it down.

Near Carmel, silt-filled San Clemente Dam was ripped out in 2015.

Our descendants will be blowing up a lot of old dams and cursing us.

The state should be trying to clean out some rooms rather than just building new houses.

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