Dam Destruction

How a dam’s destruction is changing environmental landscape

Like a giant cookie disappearing bite by bite, a massive and once-mighty concrete dam is quickly disappearing in a tucked-away corner of Monterey County.

Knocking down dams is all the rage these days, ever since Hoover Dam went kablooie in that big earthquake movie. But this time, it’s the real thing. In fact, the destruction of the San Clemente Dam could be a model for state water policy. And it’s certainly going to make a lot of steelhead trout happy.

“This is very satisfying,” said project manager Aman Gonzalez, who is overseeing the destruction of the dam as several excavators grabbed pieces of it in their giant steel teeth. “You don’t get to do something like this every day.”

For 92 years, the concrete dam topped with graceful arches just east of Carmel Valley has held back the modestly raging Carmel River and supplied water to Monterey and much of the county. But after state inspectors declared the dam a seismic hazard in 1992 — and after the reservoir behind the dam filled nearly to the top with silt — it was time to call in a half-dozen excavators and two 16,000-pound pneumatic hammers to knock it down.

The hammers clang, the excavators roar, the river babbles. Giant machines chew up boulders and spit out the pebbles like watermelon seeds. Trucks roar up and down narrow roads.

It was quiet once in the forest primeval. One day it will be quiet again, but it isn’t quiet now. It’s also the best show in Monterey County. Sadly, it’s not open to the public. You need a hard hat, a yellow vest and a special invitation to watch.

“It’s fun to knock things down,” said Jeff Kroeker, president of the company hired to do the heavy demolition. “People spend a lot of time and effort building and rebuilding a structure. But you only get to tear it down once. You have to do it right the first time. I spend a lot of time looking at buildings, trying to figure out the best way to get rid of them.”

In this case, the best way was to start at the top right corner of the 106-foot-high dam and whack away with the pneumatic hammers, being very careful not to whack away so much that the pneumatic hammers themselves topple into what’s left of the San Clemente Reservoir.

After that, the giant orange and yellow excavators — the same type that look like the T. rexes that just got done chewing up Candlestick Park — take their turn. They grab the great gray chunks that remain of the dam and shake them into submission, like a St. Bernard shaking a chew toy.

“When you knock something over, you see the results right away,” said Kroeker. “And if you didn’t wreck something, you couldn’t build something else in its place.”

Pneumatic hammers

In this case, however, the idea is to replace the dam with nothing. Water for the county will come instead from existing underground wells. The huge pile of sediment — 2.5 million cubic yards of muck — will be allowed to remain in place. It’s no longer a hazard, because the Carmel River is being diverted around the pile through a series of pipes, a new stretch of riverbed and an elaborate fish passageway designed to make things easier on the steelhead trout that annually swim upriver to spawn.

All this time, the fish have had to rely on a fish ladder at the base of the dam that is the steepest in California, and that could be the reason only 20 steelhead made it to the top in recent years, according to state fish counters. When the dam is removed, sometime later this month, the fish ladder will be replaced with 56 cozy, state-of-the-art step pools to make life easier for the long-abused steelhead of the Carmel River. The pools will be ready to welcome its first steelhead this winter. Fish experts predict the number of steelhead could double next year — to 40 fish.

“This project is a very high-ticket item for the fish,” acknowledged fish biologist Dan Wilson of the National Marine Fisheries Service. He said the steelhead should like the many fine features of the step pools, which will be a shaded, naturalistic environment “where a steelhead can learn how to be a steelhead.”

Source: San Francisco Chronicle

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