FOLSOM LAKE (CBS13) — It’s a massive multi-year construction project hidden in a man-made canyon at Folsom Lake.

There are actually two sets of gates for each bay. One is the bulkhead—a large flat gate—for holding back water for maintenance and safety. And a tainter gate, regulating the flow of water to the American River.

The massive tainter gates are shaped like a piece of pie and are about 45 feet by 40 feet and about more than 28 feet wide.

The gates are being manufactured 600 miles from Folsom by Oregon Iron Works near Portland.

The tainter gate is about 300,000 pounds and the bulkhead gate is around 200,000 pounds.

The precise work must be watertight.

The first bulkhead gate as already made its way down to Dunnigan. Thursday night it will move again, this time down Interstate 5 and east on Interstate 80 and over Madison Avenue to the dam.

Once it’s on Madison Avenue, there will be rolling street closures as the truck passes through.

Why Is A New Dam Being Built?

Sacramento County is the most at-risk area in the country for severe floods, and Folsom Dam has some existing flaws when it comes to flood protection.

Currently, the US Army Corps of Engineers requires Folsom Lake be kept at about half-empty in the winter months, no matter what the forecast says.

That’s because the height of the gates would prevent water releases in a high-flood event.

The new dam will change that.

“We are building a new control structure that has six bulkhead gates and six tainter gates that are lower than the gates on the main dam,” said  Beth Salyers with the U.S. Army Corps Of Engineers. “So it’s going to give us the ability to start releasing water sooner in anticipation of a large storm event.”

It’s also for dam safety.

“Because we are able to release up to 312,000 cubic feet of water per second if we anticipate a probable maximum flood that we fear my overtop the main dam, we would be able to release more of the water,” said Salyers. “So in conjunction with the main dam we’d be able to release the probable maximum flood is going to bring in.”

While the new dam is strictly for flood control, it could help in drought years too. In the future, they may be able to keep the lake at a higher level year-round, instead of keeping a huge amount of empty space for storm runoff.

The new dam will allow them to react sooner, and release more water in case of a catastrophic flood situation.

How Big Is This Project?

It’s hard to capture the sheer size of the project. Even when you drive by, you can’t se much.

From the Folsom Lake crossing, you generally see a construction site and wonder what’s going on over there. That’s where they’re working on the auxiliary spillway, and it is big.

When the structure is done, it will be nearly 150 feet tall.

To give some perspective, from the bottom of the concrete footing, which is partially buried, to the top, the new control structure is 12 feet taller than the Statue of Liberty.

The auxiliary spillway to the main dam will work with the main dam for releasing water.

Before they began building the dam, they had to make room for it by blasting away rock to build a canyon. Then, they started pouring concrete—a lot of concrete.

“If you were to fill up concrete trucks between Reno and San Francisco, that’s about how much concrete we’re using,” a worker said.

They are also using tons of steel in the new auxiliary dam. In fact, it’s enough steel to build two and a half Eiffel Towers.

When the new dam is completed, the gates will be capable of releasing 312,000 cubic feet of water per second. A cubic foot is about the size of a basketball, so imagine 312,000 basketballs spilling out of the dam every second.

That much water could fill four Olympic-size swimming pools in one second.

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