9604

• UCREFRP Catalog Number: 9604
• Author: Montgomery Watson.
• Title: Yampa River Basin Small Reservoir Study - Final.
• USFW Year: 2000.
• USFW - Doc Type: Steamboat Springs, CO.
• Copyright Material: NO

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I W,WP/OH~-"SoJy(Dr<(tRpr.12.21.")
/2/21/99SLW

February 2000

CR WCD .. Yarnpt Riter Basin SmaD RI!Sl!IWir Study .. Pa[!? * 1

1.0

INTRODUCTION

In January 1999, Montgomery- Watson (MW) was retained by the Colorado River Water Conservation
District (River District) to identify potential small storage opportunities in the Yampa River basin.
Initially, small storage was defined as reservoirs with capacity ranging from 500 to 2,000 acre-feet (ac-
ft). Based on discussions with basin stakeholders in early 1999, the River District modified the range,
reducing the minixmun size to 200 ac-ft. The minimum size was reduced to include smaller projects
with high development potential in the evaluation. The study is designed to assist water managers in
identifying future potential water storage opportunities in the Yampa River basin.

1.1

BACKGROUND

The Yampa River is a major tributary to the upper Colorado River system, contributing approximately
1.6 million ac-ft of water annually to the Green River at its confluence in Echo Park in Dinosaur
National Park. Figure 1, StudyArea, shows the general project area.

The Yampa River drains an area of approximately 9,500 square miles in northwestern Colorado and
south-central Wyoming. In Colorado, most of Moffat and Routt counties, along with small sections
of Garfield, Grand and Rio Blanco counties drain into the Yampa River. Portions of Carbon and
Sweetwater counties in Wyoming are drained by the Little Snake River, a major tributaty entering the
Yampa River downstream of Mayben, Colorado. This study only covers those portions of the basin
that are located in Colorado. The study area also includes Vennillion Creek, which is tributary to the
Green River in Browns Park. While Vennillion Creek is not technically part of the Yampa River
basin, it is within the River District's boundary-, and is included in this study because of its'
geographical proximity to the basin.

In 1922, the waters of the Colorado River basin were apportioned by the Colorado River Compact for
use between the upper and lower basin states. The upper basin allocation was further apportioned by
the Upper Colorado River Basin Compact of 1948 (1948 Compact). This compact addressed
allocation of the Yampa River between Colorado and Utah, and stipulates that Colorado users will not
cause the Yampa River at the Mayben gaging station to be depleted below an aggregate flow of 5
million ac-ft (maf) for any period of 10 consecutive years. Hydroshpere (1993) reported that the
average annual historical flow at the Mayben gage is 1.135 maf and the minimum historical10-year
swn is 9.1 maf.

Water use in the basin currently depletes about 120,000 ac-ft annually (BBC Research & Consulting
[BBC], 1998). Based on historic flows and the current depletions, Yampa River basin water users
claim that the 1948 Compact would allow in the range of 300,00 to 700,000 ac-ft of additional
depletion annually, dependent upon basin flow (T. Wright Dickinson, personal communication,
1999). Biological studies by the United States Fish and Wddlife Service (USFWS) have suggested that
depletions of this magnitude will impact stream flows in the lower Yampa River. The depleted flows
could result in sub-optimal conditions for fisheries and potentially adversely affect four native species
listed under the Endangered Species Act (USFWS, 1999).

The four fish species endemic to the Colorado River basin listed under the Endangered Species Act
are the Colorado pikeminnow (Pt;dxx:heilus Iucius), bonytail (Gila e/egtms), humpback chub (Gila cypha),
and razorback sucker (XyraucJm texanus). The Yampa River contains some of the largest remaining
areas of natural habitat for these endangered fish species, especially the humpback chub. It also
contributes significant flow to habitat areas in the Green River (USFWS, 1999). Concerns were raised
that strict enforcement of the Endangered Species Act could impact future water development and
the allocation of water under existing laws and interstate compacts. This resulted in the Secretary of
the Interior, Administrator of the Western Area Power Administration, and governors of Colorado,

Morztgmery Watson Mining Group . P.O. Box 774018 . StJ!drrIixJrJt Springs, Colorado 80477.[phone]