9700

• UCREFRP Catalog Number: 9700
• Author: Hayes, J.W., K.E. LaGory and G.L. Burton.
• Title: Consideration of site-specific floodplain inundation thresholds in implementing peak flow magnitude and duration recommendations in the middle Green River, Utah.
• USFW Year: 2005.
• USFW - Doc Type: Argonne National Labortory, Argonne, Illinois.
• Copyright Material: NO

Green River Floodplain Inundation

1

June 2005

1 INTRODUCTION

As part of the ongoing effort to recover endangered fishes in the Upper Colorado River
Basin, flow and temperature recommendations were developed for the Green River downstream
of Flaming Gorge Dam (Muth et al. 2000). The goal of these recommendations was to provide
seasonal and annual patterns of flow and temperature in the Green River that would enhance
populations of endangered fishes. The recommendations identified the desired magnitude,
duration, and timing of both spring peak flows and summer through winter base flows for three
reaches of the river under various hydrologic conditions, as well as recommendations related to
water temperatures.

Floodplain areas inundated and temporarily cOlmected to the main channel by spring peak
flows appear to be important habitats for all life stages of razorback sucker (Xyrauchen texanus),
and the seasonal timing of razorback sucker reproduction suggests an adaptation for utilizing
these habitats. The frequency, magnitude, and duration of seasonal overbank: flooding in the
Green River has been substantially affected by the operation of Flaming Gorge Dam and by the
formation and construction of levees between floodplains and the main channel. It is anticipated
that restoring access to these warm and productive habitats, which are most abundant inthe reach
between Split Mountain and the upstream end of Desolation Canyon, would provide growth and
conditioning environments that are important for the recovery of self-sustaining razorback sucker
populations.

For Reach 2(1) of the Green River, Muth et al. (2000) recommended that peak flows be of
sufficient magnitude, duration, and frequency to provide inundation of floodplain habitats,
provide access to those floodplains by razorback sucker larvae, and allow escapement of older
individuals that had matured in those habitats. Additional considerations included peak flows
that were sufficient in magnitude and frequency to maintain in-channel habitats.

Although inundation of floodplain habitats is considered most important for recruitment
of the razorback sucker, it has been hypothesized that such inundation would benefit all native
fish species by providing growth and conditioning environments and by restoring ecological
processes dependent on periodic river-floodplain connections. Muth et al. (2000) recognized that
access to floodplain habitats could be achieved through a combination of increased peak flows,
extended peak-flow duration, lower bank: or levee heights, and constructed inlets. The flow level
necessary for floodplain inundation varies by reach, but flow recommendations focused on the
portion of Reach 2 within Ouray National Wildlife Refuge and the upper portion of Reach 3(2)
between the White River and upper end of Desolation Canyon because the largest expanse of
potentially flooded habitat occurs in these areas.

Muth et al. (2000) recommended that information from new research should be used in
an adaptive-management framework to refme flow recommendations. In this paper, we draw on

(I) Reach 2 is defmed as the Green River from the confluence of the Yampa River to confluence of the White River.
(2) Reach 3 is defined as the Green River between the confluence of the White River and the confluence of the
Colorado River.