Q ..
What happens when these things fill up, what do we do then?
That's been a subject of a lot of debate. People have talked about, "Well, hey, why not
A
Well,
empty them. As they fill up why not go in there and remove all the material.
that's fine when you're talking about debris dams out in California, the purpose of those
debris dams is to capture all this debris and let the flood waters go on downstream.
They don't really store the flood waters, they just capture the big rocks and trees and all
that kind of debris to keep it from going down into the nice concrete-lined channels that
we built through Los Angeles. If those big boulders go bouncing down there, they raise
hell with the concrete channel.
So after you have a major flood of some sort, the debris dam is all filled up and what do
you do with it? Well, the local people have to get rid of it so it will be ready for the next
flood that comes along. Otherwise, it's not going to serve any purpose.
the boulders
will go right over the top of it.
So for years the city and the Los Angeles Flood Control District had people they could
give that debris to. People wanted it for fill in highways and places like that. New
developments where they wanted to smooth out a bunch of valleys or something, they'd
use that debris and fill in with other material, highways, and all kinds of places. But even
before I retired, they were having problems, starting to find [it] very difficult to
a
place to get rid of it.
So what did they do with it? If you can't find any place to get rid of it, it gets more and
more expensive all the time. At
it was a giveaway. Then pretty soon people started
charging you for storing it. So, anyway, that's one of the other ticklish problems you
have in California. Trying to estimate how much debris is going to come with one of
those storms is a tough problem because in most of those watersheds, there is vegetation
in there that gets drier than hell in the summertime.
Then some camper will go up there and throws a match, and the whole thing will go up
in a fire. Immediately after those fires, the capability for debris load coming down the
watershed--it'll be maybe 10,000 times greater than it was the day before. So for some
time until the vegetation grows back, the potential for debris coming down there is just
tremendous. You can't possibly build a debris dam big enough to hold all that stuff or
design it for right after a
you have to design it for some period after a
like
years, and estimate the debris from that. Design it for that because there is no way you
could do it otherwise.
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