7733

• UCREFRP Catalog Number: 7733
• Author: McAda, C. W.
• Title: Evaluation of Aerial-Video Measurement of Backwaters as Part of the Interagency Standardized Monitoring Program for Age-0 Colorado Squawfish.
• USFW Year: 1993.
• USFW - Doc Type: \
• Copyright Material: NO

Backwater Area
RESULTS
Tables 3 and 4 present mean-daily streamflow on the dates when YOY sampling was
done and when video was collected. In general, video acquisition and YOY sampling
occurred within reasonably close time frames. However, scheduling conflicts meant that
sampling within at least one reach each year was done a week or more before or after video
collection. Also, collection of video went fairly quickly (several reaches could be done in
one day), but ISMP sampling required four or five days in the longer reaches. These
differences meant that streamflow could change substantially between the time when video
was collected and ISMP sampling was done. Another complicating factor involved the
distance between parts of some of the reaches and the stream gauge for that reach. Stream
gauges in reaches 1, 3, and 4 are at the upper ends of the reaches. The lower limits of these
reaches are 95 to 117 miles downstream. Travel time for flows typically experienced during
ISMP sampling are about two days for that distance (U.S. Geological Survey, Moab, UT,
personal communication), so streamflow could be quite a bit different in the lower portions
of the monitoring reaches than that actually measured at the gauge. Additional variation
could come from unmeasured floods in side canyons downstream from the stream gauges.
Potential differences caused by the long travel time or downstream inflow could not be
accounted for in these analyses.
Video was collected in reaches 2 and 3 in one day during all years of video collection.
However, reaches 1 and 4 required parts of two days in most years (three days in Reach 1
during 1990). This allowed streamflow to vary during the time video was being collected
(Table 5). Fluctuation in mean-daily streamflow during video collection varied from 0% in
reaches 2 and 3 to a high of 39% during 1990 in Reach 1 (primarily because video in the
lower 15 miles of the reach was taken 30 days later than the rest of the reach).
Measured flow changes between video and ISMP sampling periods varied from a low of
2% in Reach 3 during 1991 to 67% in the same reach during 1990 (Table 5). Five sets of
data involved less than 10% change in flow and three sets of data involved flow changes of
40% and greater. These variations in streamflow could cause substantial changes in
backwater area between video flights and ISMP sampling. There is no way to estimate what
these differences might be because river elevation and backwater area would vary differently
at every backwater site. Small changes (< 10%) in streamflow are probably within normal
error associated with this type of analysis, but larger changes could introduce substantial
error into any calculations.
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