9389

• UCREFRP Catalog Number: 9389
• Author: Birchell, G. J., K. Chrisopherson, C. Crosby, T. Crowl, J. Gourley, M. Townsend, S. Goeking, T. Modde, M. Fuller and P. Nelson.
• Title: The Levee Removal Project
• USFW Year: 2002.
• USFW - Doc Type: Assessment of Floodplain Habitat Restoration in the Middle Green River.
• Copyright Material: NO

f. Determine the response of riparian vegetation to levee removal, and the
effects on the above-mentioned responses.
3. Measure responses in manipulated sites.
a. Determine the importance of timing and duration of inundation to native and
nonnative fish production
b. Determine the effectiveness of different gears in capturing different life stages
of endangered fish (razorback suckers).
c. Determine the response of the river fish community (native and nonnative
species) following experimentation within the manipulated sites.
Sampling efforts were initiated in 1996 prior to levee removal and continued
through 1999. Levees were breached at 3 sites in 1997 and at an additional 5 sites in
1998. Breaches were cut to match pre-Flaming Gorge Dam flooding frequency (2 out
of 3 years). Most breaches were cut at the downstream end of floodplain sites.
However, this configuration did not maximize larval transport to the floodplain because
transport was limited to days of increasing river flows. To maximize larval entrainment
sites should be configured to allow water to flow through the site.
Physical, nutrient, water quality, primary productivity, secondary productivity, and
fish data were collected both within the floodplain sites and the adjacent river reaches.
Net Primary Productivity (NPP) in the Green River was lowest in April prior to spring
flooding, then increases through the summer until peaking in July. This pattern is
attributed to increased temperatures and light penetration that occurs during this period.
NPP in the floodplain followed this same pattem although rates were much higher.
Primary productivity was highest in the floodplain following connection with the river.
Because peak productivity in the floodplain occurs post-flood, and because of a
relatively short duration of connection, floodplain habitats may not be an important
source of primary productivity for the Green River.
The overall observed pattern for benthic invertebrate densities in the river is one
of decreasing density from pre- to post-flood. Benthic invertebrate densities were
higher in the river than the floodplain prior to and during spring flooding. Following
spring flooding densities were higher in the floodplain. Export rates of benthic
invertebrates from the floodplain were very low. For benthic invertebrates restored
wetlands represented sinks of biomass rather than sources. Conversely zooplankton
were exported from the floodplain at densities up to eight times those observed in the
river. Zooplankton densities were higher in floodplain than riverine habitats during the
entire pre- to post-flood sampling period.
Non-native fish dominated the fish assemblages in floodplain habitats comprising
over 98% of the total catch. Because fish populations persist year round in depression
sites non-native densities were higher in these sites than terrace sites. The trend for
depression sites is an initial increase of non-native cyprinids (mainly fathead minnows)
followed by increasing numbers of black bullheads and green sunfish. As bullheads
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