7632

• UCREFRP Catalog Number: 7632
• Author: Pucherelli, M. J., J. N. Halls and R. C. Clark.
• Title: Green River Channel Mapping Study, 1987.
• USFW Year: 1987.
• USFW - Doc Type: \
• Copyright Material: NO

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that there were any changes in channel morphology between 1963 and
1964. The 1974, 1978, and 1986 photographs cover the entire study
area. All photographs are black and white, at various scales:
1952 - 1:20,000; 1963 - 1:24,000; 1974 - 1:31,680; 1978 1:33,000; and
1986 - 1:24,000.

Each photograph was fitted with a mylar overlay on which the photointerpre-
tation classes were drawn. The river channel was delineated by drawing
the high-water embankment lines and vegetated islands. Following photo-
interpretation, polygons were transferred to U.S. Geological Survey
standard map quadrangles. A map-o-graph transfer machine was used
to adjust the photographs to 1:24,000 scale. To maintain accuracy,
all roads, trails, and creeks on the photographs were matched with
the roads, trails, and creeks on the map bases. To calculate the length
of each reach of the river, a line was delineated through the middle
of the channel. This calculated length was used to determine average
channel width rather than estimated lengths in the Green River Wilderness
Desolation River Guide. The data were then digitized into a GIS (Geographic
Information System) using the GES (Geographic Entry System) software.
Acreage listings for each class in each year were tabulated, and black
and white map plots at 1:24,000 scale were produced for each 7.5 minute
quadrangle and each year.

The river was divided into alluvial and nonalluvial segments as delineated
by Joe Lyons, 0-753. River-miles 190 to 170 are alluvial, 170 to 142
are nonalluvial, 142 to 117 are alluvial. Allowing for the discontinuous
nature of the 1952 photography, three sites were analyzed for changes
in predam channel morphOlogy: site l--river-miles 190 to 170 (alluvial),
site 2--river-miles 170 to 166 (nonalluvial), and site 3--river-miles
123 to 117 (alluvial). Four sites were analyzed for changes in postdam
channel morphology: site 1--river-miles 190 to 170 (alluvial), site 2--
170 to 142 (nonalluvial), site 3--142 to 131 (alluvial), and site 4--128.3
to 117 (alluvial). Total alluvial river-miles analyzed were 41.8 and
total nonalluvial river-miles were 27.4.

The errors associated with interpreting aerial photography are the
consistency of the interpreter(s) and pencil line widths. Minimizing
incorrect boundary delineation is accomplished when only one interpreter
is used in making consistent subjective boundary decisions. One tenth
of 1 inch represents 200 feet at 1:24,000 scale aerial photography,
and the average pencil width represents approximately 10 feet. Therefore,
when one interpreter is used, photointerpretation of the range of scales
used in this study is accurate to within t20 feet. Additional error
can be found in the transfer and digitizing procedures. The transfer
process produces map products at the correct scale; however, the geographic
placement may be slightly incorrect. The digitizing process has been
proven to be highly accurate with very complex data sets, and this
data set is believed to be almost 100 percent accurate. There is no
method to numerically determine the error involved in either the transfer
process or the digitizing process. In conclusion, we believe that
with the scale of the photography used, all results reported in this
paper are accurate to t20 feet.