Water Resources: Hydraulics and Hydrology
It was
and
all three. We found some things on the Arkansas River
A:
cutoffs that were unexpected. When you excavate a cutoff, the river is shortened and the bed
slope is steepened through the cutoff. The short, steeper reach has greater sediment transport
capacity, and the bed slope adjusts. It was expected that the channel upstream of cutoffs
would degrade as the slope adjusted. Our data indicated that the cutoffs had little effect at
that time (1963) on lowering the stage-discharge relationships or modifying the riverbed
immediately upstream or downstream of the cutoffs. The sharper the bend, the shorter the
cutoff, and we speak of the ratio of the old bend length to the cutoff length.The shorter the
cutoff is compared to the old bend length, the larger the length ratio is, and the more
degradation. You would expect to have degradation at the head end of the cutoff, and we just
didn't get it. We had some cutoffs that had been in place for some twenty years at that time.
Was that an unusual result?
A:
Yes, it was different from what we expected to
and different from what they thought had
occurred on the Missouri.
How about the Mississippi with its cutoffs. Did they show the same results as the Missouri?
A:
I really don't know about that. I think, in general, the Mississippi cutoffs, except for a
couple, are not of the same type.
Because they don't like to stay where they are?
A:
That's right. The river's flowing downstream and the bank on the outer (concave) side of
the bend will erode. Bank erosion usually occurs along the downstream part of the bend.
And they deposit on the.
A:
On the inside. The sediment eroded on the concave bank, generally, deposits in the next
bend downstream, yes. There is a lot of sediment movement along the channel, but it isn't
the same particle of sediment that moves all the way through.
Dardanelle Dam
Q ..
So by the time you left Little Rock you were a sedimentation expert?
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