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

Overbank and Bottomland Flooding Observations
Green River
The aerial photos presented in figures 3-5 do display the extents of the 1997 flooding at approximately
25,000 cfs rather well. The SR/FT site did not receive any overbank flood flows due to the man-made
levee road. The stage of the river would have had to increase roughly two more feet to overtop the levee.
Some seepage was observed at the lower end of the site. However, none of this water got over one foot
in depth. It is assumed that this seepage occurs annually during runoff season, as it was evident when
the Green River was at approximately 7,000 cfs.
From the Green River at Jensen data, we can also conclude the approximate duration of flooding at the
other sites. For the SN site, which floods at approximately 17,000 cfs, a connection to the river that
provides fish passage to the floodplain habitat, is developed when flows exceeded that quantity. That
flow was exceeded for 40 days during 1997 according to the USGS data. Similarly, flows of 19,000 cfs
were exceeded for 24 days, allowing fish passage to the Intermountain Concrete site, and flows of 19,600
cfs were exceeded for exceeded for 21 days, providing fish passage to the SL site.
During 1998, the peak flows were lower. The peak flow was approximately 17,000 cfs, which was
exceeded for approximately two days based on provisional data. Therefore, only the SN site may have
developed a connection to the river sufficient to provide fish passage. However, it was observed at the
SN site that overbank flows are conveyed to the MU property through a culvert between the SN/MU sites
when overbank flow stages increase.
Gunnison River
Flooding observations for the Gunnison River were fairly limited. The Dad's Flat site has naturally high
banks that did not come close to overtopping 1997. The BC site has the man-made levee that was well
above any flows exceeded in 1997. Neither site was visited during the 1998 runoff season.
Colorado River
Flooding observations were also limited for the BO/BR ponds. Both are well protected by the man-made
dike. The BR pond is not significantly affected by groundwater connections. The water surface elevation
of the BO pond rose 3 feet from March to the end of May 1998. For comparison, the river rose 4.2 feet
over the same time period. Therefore, there is a significant groundwater connection for the BO pond/pit.

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