7049

• UCREFRP Catalog Number: 7049
• Author: Andrews, E. D.
• Title: Present and Potential Sediment Yields In THe Yampa River Basin, Colorado and Wyoming.
• USFW Year: 1978.
• USFW - Doc Type: \
• Copyright Material: NO

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fror> 10 to 1~ inc:.es (250 to 360 rllm) of preCipitation annually. A comparison
of figures 5 and 8 sho\./s tr;at the areas of large sediment yield are also
those areas ~h;ch receive from 10 to 14 inches (250 to 360 mm) of precipita-
tion annually. Sediment yields decrease eastward as precipitation increases,
and the smal lest sediment yields are from those areas that receive the most
precipitation.

Comparison with Estimates by Other Investigations

A sediment-yield map of Colorado \~as prepared by the Colorado Land Use
Commissicn (1913) u;'ing the Pacific South~est Inter-Agency Committee (1968)
or PSIAC method. Th~s me~ho~ d~velops a numeric~l rating of the potential
erodibi 1 ity of a watershed in ninecategories, as shown in table 3. The
e:-osion rate is esti'Jl.a.ted by c~nlparing the numerical score with the measured
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erosion rate of drainage basins I.:ith a similar score.

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Sedimen~ yields were computed at the 17 qaging stations In the Yampa
River basin from the Colorado State~map. The percentage of a subbasin in
each level of erosion was determined. and then the average erosion rate for
the drainaqe. In order to obtain-an accurate estimate at each station, the
average e~osion rates must be adjusted to the drainage area. Brune (1948)
shov:ed that, other factors being constant, sedinent yields (Y ) vary inverse-
ly l'lith drainage area (/1) to the 0.15 pOl-ler: 8

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The erosion rate determined by the PSIAC method appl ies to a drainage area of
1 mi2 (2.59 kn2). Hence, the average erosion rate (Y,) for a given drainage
area must be nultipl ied by

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to give the estimated sediment yield (Y,) at the qaginq station.
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A c0mparison of the sediment yields co~puted In the investigation
(abscissa) with the sediment yields determined by the PSIAC method (ordinate)
I S s h O\.:n ! n fig u r e 9. The rei s con sid era b 1 e s cat t era r 0 u n d the I i n e, 0 f
agreement, an~ no consistent relation between the two methods is apparent.
Thus, although sediment yields estimated bv the PSIAC met~od may agree with
the average of several nlcasured sediment yields, the PSIAC method probably
will not provide a good estimate of the actual sediment yield for a specific
location.

The measured sediment yields
i compared with the Langbein-Schumm
\\ mean-annual precipitation for each
,

in the Yanoa River basin also may be
(1958) relatio;1 sho',:n on figure 6. The
of the 17 subbasins was determined from

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