8260

• UCREFRP Catalog Number: 8260
• Author: Elliott, J. G., D. M. Murphy and K. S. Tucker
• Title: Resource Management Considerations in a Changing Physical Environment
• USFW Year: n.d.
• USFW - Doc Type: The Gunnison Gorge, Colorado
• Copyright Material: NO

Park reach. The location of all-optimal trout-production reach may not be static, even under
regulated streamflow conditions. Sustained reservoir releases of 8 to 10 m3/s in years of
less-than-average precipitation are characterized by warmer temperatures, and the reach of
optimal trout production shifts upstream toward the BOLA western boundary (J.A.
Stanford, Director, Flathead Lake Biological Station, Polson, Montana, personal
communication, 1993). Sport fishermen, seeking optimal fishing, likewise move into and
have impacts on less-frequently used reaches of the Gunnison Gorge.
RESOURCE USE AND BLM MANAGEMENT
The BLM places a high priority on both protecting the unique wilderness qualities of
the Gunnison Gorge and accommodating wilderness recreation activities. Gunnison Gorge
visitation more than tripled between 1986 and 1991, increasing from approximately 5,000 to
over 15,000 visitor days per year. Approximately 10,000 visitor days in 1991 were
attributable to recreational activities on the river or in the riparian zone. Interest in the
diverse natural resources of the area and the increased numbers of visitors whose
recreational activities often overlap or conflict has lead to increasing effects on the natural
environment.
The BLM's management objectives are being implemented in the context of annual
and seasonal uncertainty in available streamflow and continuously evolving geomorphic
and riparian conditions. Bank stabilization, vegetation encroachment, bed-material
armoring, debris-fan constriction, and enhancement of rapids all affect where and how
different areas of the Gunnison Gorge are used by visitors. Seasonal hydrograph
characteristics also affect the type, time, and volume of visitor use, but are difficult to
predict. Reservoir operation is determined by the snowpack water content and runoff
forecasts, water-storage requirements and optimal reservoir volume, flood control in wet
years, downstream (Colorado River Compact) water claims, and diversion for irrigation.
Proposed reservoir releases are ar-nounced to the public in the winter and spring by BOR,
but releases often are adjusted throughout the runoff and recreational season. Long-term
budgeting and efficient allocation of BLM resources are made difficult because management
and enforcement expenditures are determined partly by visitor use that varies with
changing river conditions. _
Visitor use, river conditions, and streamflow-dependent processes related to
discharge range and recurrence interval are presented in Table 1. Upper and lower limits of
the five discharge ranges are approximate and are intended as references only. Some
streamflow-dependent conditions and processes overlap interval boundaries. The
information in Table 1 is based on field observations, theoretical calculations, and patterns
of visitor use. Qualitative descriptions of the discharge ranges (low flow, etc.) are based on
the frequency of occurrence and flow duration since 1966.
Low-flow reservoir releases, resulting in discharges less than 30 m3/s, have occurred
more than 55 percent of the time since 1966. Low-flow conditions usually occur from late
summer through spring, but can persist through summer in years of below-normal
precipitation. Suspended-sediment load tends to be low; however, suspended-sediment
concentration can be high and large numbers of fish can be killed when tributary floods
introduce a large volume of fine sediment during low-flow conditions. Fine sediment, when