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Last modified
7/14/2009 5:02:33 PM
Creation date
5/20/2009 3:30:26 PM
Metadata
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UCREFRP
UCREFRP Catalog Number
8110
Author
FLO Engineering, I.
Title
Green River Flooded Bottomlands Investigation Ouray Wildlife Refuge and Canyonlands National Park, Utah-Final Report.
USFW Year
1996.
USFW - Doc Type
Breckenridge, CO.
Copyright Material
NO
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<br />position of sand bars and scour holes in the channel recurs from year to year. The relatively e <br />stable position of the sand bars during high flows has also resulted in vegetation establishment <br />and eventual attachment of the bars to a bank or island. <br /> <br />One process that alters the scour and fill cycle is the movement of sand waves or slugs <br />through the system. This was noted in the Escalante Wetlands study near Dinosaur during the <br />high flows in 1993. There, a large wave of sand entered the reach forming large sand bars and <br />greatly modifying the cross sections for several miles. These bars remained throughout the low <br />flow season (FLO, 1994). In this case, there was an adjustment in the channel geometry to the <br />varying sediment load. <br /> <br />Three sets of cross section surveys were conducted at the two study sites: late March, late <br />May and mid-September, 1995 at Ouray; and, mid-April, mid-June and mid-September, 1995 at <br />Canyonlands. The data collection occurred at approximately equal discharges for the spring and <br />fall surveys and at approximately the peak discharge for the May-June surveys (Table 2). Table <br />3 presents a summary of channel changes observed throughout the runoff period. The changes <br />were identified by reviewing superimposed cross section plots for the three data collection <br />periods. These plots are provided in Appendix A. The USGS provisional gaging station data <br />from the Green River gage and the San Rafael gage were added together to estimate the <br />discharge in Canyonlands. Unfortunately, the USGS discharge data was provisional and this <br />data may be adjusted in the future. FLO Engineering measured 20,630 cfs in Canyonlands on <br />June 4; however, reported provisional flows at the Green River gage at Green River did not e <br />exceed 20,000 cfs until June 6. San Rafael flows during this period were 100 cfs or less. <br /> <br />Channel Response in Ouray Reach to 1995 Runoff <br /> <br />The 1995 water year can be considered as near-average. The Jensen-gage-recorded peak <br />flow of 18,600 cfs on June 19, 1995 was only 7% higher than the average annual post-1963 peak <br />of 17,430 cfs. The peak flow return period for 1995 was estimated at 3 years. The overall <br />qualitative response in the Ouray study during 1995 was net deposition in the channel from <br />March to September. <br /> <br />Out of a total of 36 cross sections, 17 cross sections experienced no significant net scour <br />or fill, 13 cross sections had some net fill while only 6 cross sections showed net scour. The <br />cross section plots are presented in Appendix A. Six of the 36 cross sections developed a <br />significant sand bar extending into the channel, ranging up to 200 ft in width and up to a 12 ft <br />change in bed elevation. In addition, several of the cross sections experienced thalweg filling. <br />The maximum scour surveyed was 13 ft at cross section LEB 24. Although almost every cross <br />section was modified to some degree with scour and/or fill, most of the cross sections did not <br />experience a major net change in bed elevation. Although net fill was noted in the study reaches <br />over the course of the 1995 runoff season, long term trends cannot be discerned from a single <br />runoff season. It will take many years of monitoring to reliably ascertain long term trends in the e <br /> <br />21 <br />
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