9508

• UCREFRP Catalog Number: 9508
• Author: Valdez, R. A. and P. Nelson.
• Title: Green River Subbasin Floodplain Management Plan.
• USFW Year: 2004.
• USFW - Doc Type: Lakewood, Colorado.
• Copyright Material: NO

Executive Summary

April 2004

EXECUTIVE SUMMARY

The Upper Colorado River Endangered Fish Recovery Program (Recovery Program)
developed this Floodplain Management Plan (Plan) to provide restoration and management
strategies for existing floodplain sites within the Green River Subbasin that have been acquired
and/or are managed by the Recovery Program for the benefit of the endangered razorback sucker
(Xyrauchen texanus). The goal of this Plan is to provide adequate floodplain habitats for all life
stages of razorback sucker, particularly to serve as nursery areas for larvae and juveniles, for
establishment and maintenance of a self-sustaining population. The objectives of this Plan are
to: (1) inventory floodplain habitats; (2) identify and acquire available floodplain easements; (3)
restore and manage available floodplains to benefit razorback sucker and bonytail; and (4)
evaluate the effectiveness of restoration. It is hypothesized from scientific studies and hatchery
culture that two other endangered fish species, bony tail (Gila elegans) and Colorado
pikeminnow (Ptychocheilus lucius), will also benefit from a greater availability of floodplain
habitat.

The focus of this Plan is the 107-mile reach of the middle Green River from Split
Mountain to Desolation Canyon. Historic data indicate that this reach was the population center
for razorback sucker in the Green River Subbasin. This reach has the only known spawning bar
for razorback sucker in the Upper Colorado River Basin; suitable ecological conditions for
species recovery; sufficient numbers and acreage of available floodplains; and Green River flow
recommendations to ensure floodplain inundation and long-term protection of these habitats.

Inventories show that there are 37 potential floodplain sites for a total of about 11,400
acres in the Split Mountain to Desolation Canyon reach. At 18,600 cfs, the estimated area of
floodplain inundation is 6,000 acres. Under average hydrologic conditions (i.e., 30-70% peak
exceedence), the Green River flow recommendations predict that 18,600 cfs should occur in 1 of
2 years and be maintained for at least 2 weeks in 1 of 4 average years. This Plan identifies 16
floodplain sites totaling 4,448 acres with access by the Recovery Program for restoration and
management. The Recovery Program has restored and is evaluating and managing five sites (489
acres) as long-term floodplain depressions: (1) Bonanza Bridge, 28 acres; (2) The Stirrup, 28
acres; (3) Baeser Bend, 47 acres; (4) Above-Brennan, 50 acres; and (5) Old Charlie Wash-Main,
336 acres. Long-term floodplain depressions become inundated at spring runoff and entrain
larval razorback sucker, then maintain suitable water quantity and quality for 24 months, at
which time the fish escape to recruit as adults in the mainstem. These floodplains reset
periodically by desiccating and killing stranded predaceous and competitive nonnative fishes.
Shallow depressions desiccate after a short time period, and terraces fill and drain with river
stage; neither feature is suitable as nursery or rearing habitat. There are several hundred acres of
terrace or small depression floodplains that form in this reach at 18,600 cfs to which the
Recovery Program does not have access but may serve as nursery habitat for razorback sucker.

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