8259

• UCREFRP Catalog Number: 8259
• Author: Kircher, J. E.
• Title: Sediment Transport and Source Areas of Sediment and Runoff, Big Sandy River Basin, Wyoming.
• USFW Year: 1982.
• USFW - Doc Type: Water-Resources Investigations 81-72,
• Copyright Material: NO

(P = 2.1505e-0.3910 (10)
while Brown (1950) showed that the relation
4) = 40(T)3 (11)
fits the data more closely. The Helley-Smith data conform more closely
to the Brown version of the Einstein bedload function than to the ori-
ginal Einstein function in figure 26. Using the Einstein and Brown-
Einstein bedload functions as a guide, the Helley-Smith data can be
analyzed in general terms. The data points to the right of the curves in
all instances come from streams having large quantities of both fine and
coarse sediment, with the sediment sizes in between contributing very
little to the actual sediment load. In these types of streams, the
larger particles have a shielding effect by trapping the smaller parti-
cles between them. This shielding effect causes a smaller amount of
sediment to be transported than the stream has capacity to carry. In
addition, Emmett (1979) stated that due to the Helley-Smith's size and
the paucity of large particles moving, particles larger than the sampler
nozzle are not picked up by the sampler, and the rate of movement of the
larger particles is such that they may not pass the sampling section at
the time and place of sampling. This would result in a measured trans-
port rate less than what actually occurs along the bed.
The data points above the curves indicate more transport than the
Brown-Einstein relation. A reason for this may be the inclusion of part
of the wash load in the Helley-Smith sample. Einstein included only that
part of the bedload occurring in appreciable quantities in the bed in his
development of the bedload function, which underestimates the actual
sediment load near the bed. Another reason for the large measured load
by the Helley-Smith bedload sampler may be the scooping effect the sam-
pler can have when set on the bed of a stream. This will inherently give
a larger transport rate than is actually present. Even with proper use
of the Helley-Smith sampler, it is difficult to eliminate this scooping
completely while collecting a sample.
In developing the modified Einstein relation, Colby and Hembree
(1955) arbitrarily divided the bedload intensity by two. This procedure
was applied in figure 27 to see if it improved the comparison of the
Helley-Smith bedload data with the Einstein bedload function. When the
Colby adjustment was applied to the data, there was no improvement. The
data points actually remained the same or moved further away from the
Einstein and Brown-Einstein functions. Therefore, it can be said that
the Colby adjustment did not improve the Einstein bedload function in
this case.
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