One of the best sights a flood maintenance engineer can see below a debris basin: a fast-flowing storm drain, indicating the bathtub is emptying.
A fourth day of storms will test the network of debris basins that Los Angeles County operates in the foothill cities. Those basins are collecting - and so far, holding - the mud and rocks tumbling down from the Station Fire burn area.
KPCC's Molly Peterson went to check the flood system with a public works crew.
Imagine a debris basin as a big bathtub. The bathtub's drain is a big round concrete tower that can be almost 50 feet high. Mudflows swirl around one such tower in the Hay basin above La Canada. Two guys in dirty yellow slicker suits study it. About at 5 feet right now. Yeah, about 5 feet of sediment in there with water. Lot of branches in it too. We're going to have to come back to this one for sure and clean it out. Note it.
That's Steve May and Marcos Morales. Guys in dirty yellow slicker suits. All week, they've gone out and eyeballed basins on 12 hour shifts. If debris leaves a bathtub ring, water's draining faster than mud's piling up. That's good. The drain here is slow. "We got a lot of water coming in with dirt, so, it looks like we got more water coming in a couple of minutes. So this one is going to fill up quick, in a couple of hours," Steve May says.
Arthur Vander Vis wants you to know that's not as big a deal as it might sound. Vander Vis is a top flood maintenance engineer for L.A. County. He says all 28 debris basins, including full ones, are working to protect streets and houses from mudflows off the hillsides burned by last summer's Station Fire. "We're keeping most of the debris out of the system, and the part that remains, the rest of the system can handle that," he says. "So there's no real alarm if the debris goes to spillway."
Vander Vis expects that could happen – a consequence of the vast acreage the Station Fire burned. If and when debris does pour down off the hills, crews will work to keep what's in the spillway in channels and away from property. "We beef up our patrols as it gets heavier rains, so we can patrol more often the same one location," he says.
Vander Vis is a veteran civil engineer. He says maintenance and prep is springtime work; off-season work. Now, when the rain falls, is the time to let the system do its job.
Back in the field, keys jingle, and the metal gate opens. The guys in yellow slickers, Morales and May, unlock another gate. The Halls basin is draining slowly, too. If it wasn't raining right now, we could probably poke that tower too. Just open up a couple more windows to try to get the water to drain down faster.
Because it is raining, they lock up and head out to check the next debris basin. They'll circle back later to report on this one.