9575

• UCREFRP Catalog Number: 9575
• Author: LaGory, K. E. and R. A. V. Lonkhuyzen.
• Title: Potential Effects of Four Flaming Gorge Dam Hydropower Operational Scenarios on Riparian Vegetation of the Green River, Utah and Colorado.
• USFW Year: 1995.
• USFW - Doc Type: \
• Copyright Material: NO

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4,700-cfs flows would be inundated regularly during the first half of the growing season only.
Wetland vegetation in this area would probably survive, but there could be a shift from
drought-intolerant species - such as cattail, common spikerush, and juncus - to more
drought-tolerant species - such as common reed and scouring rush. As with the year-round
high fluctuation scenario, the expected shift in the boundary between the upper and lower
riparian zones would result in a 5% decrease in the area occupied by the upper zone and a
13% increase in the area of the lower zone.
4.2.3 Seasonally Adjusted Moderate Fluctuation
Under the seasonally adjusted moderate fluctuation scenario, the lower boundary of
the upper riparian zone is expected to occur at the elevation of the 4,700-cfs flow. As with
the seasonally adjusted high fluctuation scenario, 4,700-cfs releases would occur through the
entire first half of the growing season (to July 10). Although lower flows would occur during
the last half of the growing season, any species of the upper zone that colonized lower
elevations during this period would not survive the inundation during the following year.
Under this scenario, the lower riparian zone is expected to occur between the
elevations of the 2,400- and 4,700-cfs flows. This area would be inundated daily during the
first half of the growing season, but then would be above the area of fluctuating flows from
mid July through October. As for seasonally adjusted high fluctuations, vegetation in the
lower riparian zone is expected to undergo a shift toward more drought-tolerant species
because of the extended period of low flows after July 10 of each year. The area below the
2,400-cfs level would be inundated continuously for most of the year. Any existing vegetation
below this elevation would drown, and the unvegetated zone would increase in size. Species
most likely to be adversely affected by this prolonged inundation include cattail, common
spikerush, field horsetail, juncus, and scirpus. Shifts in riparian zone boundaries and
creation of unvegetated areas are expected to result in a 5% decrease in the size of the upper
zone and a 40% decrease in the size of the lower zone.
4.2.4 Seasonally Adjusted Steady Flow
Under the seasonally adjusted steady flow scenario, the upper riparian zone is
expected to expand down to the elevation of the 3,400-cfs flow. Below this level, inundation
would be too prolonged to allow establishment of upper-zone species. The higher flows during
the spring peak would not prevent establishment of these species to the 3,400-cfs level
because higher flows would be of relatively short duration. Species most likely to increase
under this scenario include tamarisk, giant whitetop, golden aster, box elder, and artemisia.
For this scenario, the lower riparian zone is expected to occur between the elevations
of the 2,400- and 3,400-cfs flows. Areas above the 3,400-cfs level would be too dry to support
lower-zone species, except for scattered locations along the river where local conditions would
permit wetland vegetation to persist at slightly higher elevations. Species that would be
adversely affected because of drying include Canada thistle, carex, coyote willow, field