Jacob H. Douma
What was required
Make wider spillways or something that would take that junk out?
A:
We had to enlarge the openings in the trash rack so the debris would go on through.
When you do something like line the Los Angeles River with concrete, those floods are
very large flows, aren't they?
A:
Yes, they are.
Your design has to be specifically gauged to those large flows, doesn't it?
A:
Yes. We had what was called a design flood, and we designed the channel to carry the
peak flood discharge of that. The channel was constructed wide enough and deep enough
throughout its length to carry the design flood.
The Los Angeles River channel is concrete-lined, except for the lower six or eight miles
where the slopes were flatter and the velocity is not so high. Here, it was found that a less
costly method of rock lining the levees and constructing rock drop structures across the
channel every 1,000 or 1,200 feet was a lot cheaper than concrete-lined channels.
What were the problems that you might have had working on those flood control channels?
We talked about the debris problem.
A:
The drop structures had to be designed so that the water would drop about 10 feet, and
they had to be designed as part of a small downstream stilling basin. Even though the
velocity was fairly low, the river bed is nothing but sand, which might scour sufficiently
to undermine the downstream levees. Model tests were made of the drop structures to be
certain there was adequate protection. Downstream of the drop structure, some rock
protection was required to prevent excessive erosion of the sand beds.
There was a lot of work going on in the late
Yes. There was a lot of work going on then. During the time I was there, we designed
San Gabriel River channel from the mountains all the way down to the Bay. The Los
Angeles River channel construction was already completed. The San Gabriel River
channel, which was about three or four miles to the east and ran almost parallel to the Los
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