BOARD01926

• Board Meeting Date: 1/27/2004
• Description: ISF Section - Instream Flow Appropriations - West Antelope Creek
• Board Meetings - Doc Type: Memo

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Introduction

In the Summer of 2000, students in Western State College's Field Geology class (GEOL
450) had the opportunity to study the hydrology of a section of West Antelope Creek.
West Antelope Creek is located just northwest of Gunnison in the foothills of the West
Elk Mountains (Figure 1), It is located in Township 50 north, Range 2 west, blIt no
Section lines are shown for this part of the quadrangle. The reach that we surveyed is
immediately northwest of the boundary between National Forest and Bureau of Land
Management (BLM) land.

West Antelope Creek is part of the Gunnison River watershed and contains several old
beaver dams that have been breached or destroyed (Figure 2). Aerial photographs from
1977 (Figure 3) show some ponds from these beaver dams. The ponds are no longer
filled, so it appears that the beavers (Castor canadensis) died or migrated out of this
section of West Antelope Creek within the last 23 years.

West Antelope Creek is of particular importance because it supports a population of
Colorado River cutthroat trout (Oncorhynchus clarki pleuriticus), Genetic analysis
indicates that this is a genetically pure Colorado River cutthroat trout and may be the
only remnant population of trout native to the upper Gunnison River as no others have
been confirmed (Arthur Hayes, Bureau of Land Management, personal communication).
West Antelope Creek provides an important refuge for this species and channel instability
may threaten the continued existence of this population. Flow in the stream was
measured by the Field Geology class and was found to be quite small (between 1 and 2
cubic feet per second) and the potential exists for the creek to run dry in sections, We
hypothesize that the beaver ponds may have provided refuge for the trout during low-
flow periods,

The purpose of this hydrologic survey is to provide a benchmark of the physical
condition of the channel, floodplain, and terraces of a section of West Antelope Creek
that contains abandoned and breached beaver dams, and to look for evidence of
instability in the channel (i.e. excessive erosion or deposition). This survey could be used
to monitor changes in the following years. The survey was performed on June 6-8, 2000
as part of Geology Field Camp for students in the Geology Program of the Department of
Natural and Environmental Sciences at Western State College of Colorado. It is expected
that the class will return to West Antelope Creek in the upcoming years to survey
changes that have occurred. The hydrologic survey included:

Establishment of benchmarks,
. Cross-section profiles,
Longitudinal profiles,
Discharge measurements,
. Pebble counts (bed-material size).

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