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

Stage/Discharge Data Collection
Green River
In order to predict the flooding discharge of a bottomland accurately, a thorough data collection effort
conducted before and during the runoff season is preferable. This was possible at the SR site in 1997.
On four occasions during the runoff season, water surface elevations (stages) and corresponding
discharges for the Green River at Jensen were documented for the SR reach. The SR cross section
endpoints, established in April 1997, were used to determine and record water surface elevations.
Discharges ranged from 12,300 cfs to 20,400 cfs, bracketing the flooding discharges of interest.
Typically, the water surface elevations were determined at the edge of water near the top of bank on the
side of the river where the bottomland was located. Observations of the water surface relative to the top
of bank and adjacent bottomland were also documented at the different discharges. For reference,
tabulations of the recorded water surface elevations, dates, and discharges for the SR cross sections can
be found in the 1998 technical report.
Due to availability and extent of discharge data recorded by the Green River at the Jensen gage, the
Jensen data were used for the stage/discharge analyses. From the stage measurements and recorded
discharge data at Jensen, stage/discharge rating curves were developed for all six cross sections at the
SR bottomland site. The results of these analyses are detailed in Chapter Four of this report.
For the SN, IM, and SL properties, stage/discharge data were not collected during the 1997 runoff
season. A hydraulic model was developed from cross section surveys and a high water reference mark
on the Jensen Highway 40 bridge for the SN/IM properties. Similarly, a hydraulic model was developed
for the SL properties using stage/discharge data from the 1996 and 1997 data collection efforts at the
Horseshoe Bend and Bonanza Bridge sites. Additional stage discharge data was ,however, collected
during the 1998 runoff season in order to improve the modeling. Further discussion of the modeling effort
• can be found in Chapter Four of this report. For these three sites, additional stage measurements will be
collected during the 1998 runoff season to further improve the accuracy of the flood predictions
Gunnison River
Stage measurements were taken at the five BC site cross sections on six different days during the 1997
runoff season. Gunnison River flows ranged from 6400 cfs to 9200 cfs. One discharge measurement
was taken on May 21St, 1997. The Gunnison River near Grand Junction, Colorado was used for the rest
of the calibration. For the Dad's Flat site, stage measurements were taken on four occasions, with flows
ranging from 7900 cfs to 9000 cfs. One discharge measurement was performed on May 31St, 1997.- No
stage discharge data was taken at either site in 1998.
Colorado River
The BO/BR ponds were not surveyed until the fall of 1997. Therefore, the majority of the stage data were
collected in 1998. Water surface elevations (staq~es) were surveyed at cross section BR-4 on five
different days between March 12th, 1998 and July 6t , 1998. Discharges ranged from 2270 cfs to 10,200
cfs. This data was used to re-calibrate the HEC-RAS flood prediction model developed iri 1997. The
accompanying technical report has more details of the modeling.
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