Jacob H. Douma
That's that big spillway from the Mississippi River to Lake Pontchartrain.
Yes. I got involved in that. Model studies were not made because the spillway is long
and the head is low. As I recall, a low lift lock was constructed.
Okay.
But I do remember looking at the plans when they came in.
Jetties at the Mouth of the Columbia River
Any other one of these projects that you wanted to talk about that you have been thinking
about?
We haven't talked much about navigation channels. I listed here "navigation channel at
the mouth of the Columbia River. Maybe we can talk about that a little bit. Are you
with the Columbia River? It's a wide river at the mouth and a long distance.
It's got those long jetties going out, doesn't it?
Yes. It's got long jetties going out, a south jetty and a north jetty. One of the problems
involved the jetties. When they were first constructed, large rock was used to extend the
jetties seaward. The jetties were subjected to
to
high waves during storms,
which damaged the jetties by undermining the rock or eroding it away, particularly at the
ends.
For a long time, the jetties were repaired by placing more rock at the damaged areas. The
rock was very costly, because it had to be hauled a couple of hundred miles on barges.
So the Portland District was studying other more economical ways of maintaining the
jetties. The Committee on Tidal Hydraulics was asked to meet in Portland to discuss the
problem. The Committee suggested that consideration should be given to using artificial
protection like concrete tetrapods. A tetrapod is similar to a jack, made out of concrete,
with legs about 12 feet long, and they're very heavy. Their size and the weight depend
on the forces that they have to withstand.
In constructing the jetty protection, a rock base is first placed at the toe of the slope and
up the slope to the top of the rock jetty. Then one or two layers of tetrapods are placed
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