9371

• UCREFRP Catalog Number: 9371
• Author: Levee Removal Evaluation Group.
• Title: Green River levee Removal and Floodplain Connectivity Evaluation.
• USFW Year: 1998.
• USFW - Doc Type: CAP-6 LR,
• Copyright Material: NO

1
EXECUTIVE SUMMARY

important part of river ecology. They provide valuable habitat for fish
Floodplalns are an
and play a major role in nutrient cycling. Floodplain habitats are believed to provide important
habitat for razorback suckers. In the middle Green River, vast areas are flooded each spring.
However, the historic flooded area has been reduced as a result of the Flaming Gorge dam
operation.
Because of information linking razorback sucker life cycles to floodplain habitats, the
Recovery Implementation Program (RIP) initiated a floodplain acquisition and enhancement
program. Several questions were raised about the biological cost and benefits of floodplain
enhancement. The need to monitor floodplain enhancement was identified and the Levee
Removal and Floodplain Connectivity Evaluation study was created. The objectives of this
study included evaluation of reconnection of floodplains to the river, ecosystem responses to
levee removal, the use of managed sites as a tool to assess importance of timing and duration of
inundation, and to design and implement adaptive management strategies.
l
),
Sampling efforts began in 1996 prior to the enhancement activities (levee remova
and continued through 1998. Physical, nutrient, water quality, primary productivity, secondary
productivity, and fish data were collected both within the floodplain sites and the adjacent river
reaches. All results are preliminary. Many of the sites have only been sampled for one season,
and not all of the data from the 1998 sampling was available at the time of this report.
Physical and water quality data indicate that the depression sites can support fishes.
Carbon contribution to the river is important to riverine fish production, and zooplankton
provided the greatest proportion of carbon exported to the river. Total carbon export was greatly
enhanced by floodplain connection.
To date, a wide variety of native fish response has been observed. This was expected
given the relative short period of study and the complexity of the system. Despite intensive
efforts, relatively few native fishes, and very few razorback suckers, have been collected.
Reaching conclusions about native fish, or razorback suckers, responses are difficult given the
small number of native fish that were sampled.
ti
N
h
f
ve
a
es.
is
Aquatic vegetation seems to be correlated with higher densities of native
fish use of floodplains is directly related to timing and duration of peak flows. Sites that flood
from the downstream side are dependent on rising river water to fill the site and entrain fish
larvae. To entrain larvae, the river water level must rise despite the fact that razorback larvae are
drifting on the descending limb of the hydrograph. Secondary and tertiary peaks are critical in
this type of site. These late peaks on the hydrograph occurred more frequently prior to the
operation of Flaming Gorge Dam. Sites that are designed for water flow-through may be better
at entraining larval fish at all levels of flooding.
The intensive sampling efforts within the levee removal sites have resulted in the capture
and enumeration of 897,856 nonnative fish (1996-1998). Nonnative fish dominate all sites
making up more than 98 percent of the fish captured. The trend, for depression floodplain sites,
is for increasing numbers of black bullhead catfish and green sunfish. This increase is a result of
natural reproduction and recruitment within these sites. This is not surprising given the lentic
nature of these species. There is some evidence in the literature that these populations may build'
and then crash
?
.
xvii