9422

• UCREFRP Catalog Number: 9422
• Author: FLO Engineering, I.
• Title: Floodability Assessments of Private Land Sites along the Green River, Gunnison River and Colorado River.
• USFW Year: 1999.
• USFW - Doc Type: Volume IA,
• Copyright Material: NO

For example, the following equation was developed using the data collected at the SR-6 cross section:
Stage = 0.3223 Q0.3682
where, Q =Recorded discharge at Jensen Gage (cfs)
Stage =Water surface level above Gage Zero (ft)
The stage value can then be added to the gage zero (minimum elevation in the cross section) to obtain a
predicated water surface elevation for any given discharge.
Elevation =Stage + Gage Zero
Figure 9 displays the rating curve for cross section SR-6, which was used to compute the flooding
elevation, flooding discharge values, and flood inundation levels for both the SR site and the adjacent FT
site upstream of the SR site. All six SR rating curves can be found in the technical report. Table x
displays the rating curve parameters for all the SR cross sections. The coefficient of determination, RZ
value, for each derived equation is also listed in Table 1. This value indicates how well the data were
represented by the power function. The RZ values ranged from 0.9907 to 1.0000 for the cross sections.
An Rz value of 1 indicates a perfect fit, therefore, the high RZ values obtained for the rating curves
demonstrates a significant level of accuracy for any predicted water surface elevations within the range of
discharge data which were collected.
Gunnison River
Sufficient stage discharge data were collected at the BC site to create stage discharge curves for the BC
cross sections. The BC-5 stage discharge equation was calculated to be:
• Stage=4618.1 + .1181 Q.ass~
where Q= Recorded discharge at the Gunnison River near Grand Junction Gage (cfs)
Stage =the water surface level above Gage Zero (ft)
The stage value can then be added to the gage zero (minimum elevation in the cross section) to obtain a
predicted water surface elevation for any given discharge.
Elevation =Stage + Gage Zero
Figure 10 displays the rating curve for cross section BC-5, which was used to compute the flooding
elevations at the site. The remainder of the rating curve equations are listed in Table 2 and the curves
and raw data can be found in the technical report.
Calibration of a Hydraulic Model
Green River
Access rights to the SN, IM, and SL properties was not granted until after the 1997 runoff season.
Therefore, water surface profiles had to be determined using the HEC-RAS River Analysis System model
Version 2.1 (US Army Corps of Engineers, 1997). Surveyed cross section data were put into this model,
which calculates step backwater water surface profiles from which flow depths, velocities, and bankfull
discharges can be predicted. For the SN/IM reach, the high water mark on the Jensen Highway 40
bridge, which corresponds to the 1997 peak discharge, was used to calibrate the model. However, as
discussed stage discharge data collected in 1998 was used to improve the accuracy of the model. For
the SL reach, stage/discharge data were available from the Horseshoe Bend cross section (HB-4) which
was included in the model. The stage/discharge relationship for HB-4 was developed from eight stage
3-2