9504

• UCREFRP Catalog Number: 9504
• Author: Cooper, D. J. and C. Severn.
• Title: Ecological Characteristics of Wetlands at the Wetland Clough, Moab, Utah.
• USFW Year: 1994.
• USFW - Doc Type: \
• Copyright Material: NO

DISCIISSION AND MANAGEMENT ISSIIES
Hydrology
Dam construction on the upper Colorado River-and its
.tributaries has drastically altered the .flow regime of the river.
In particular the maximum annual flows are reduced in magnitude
resulting in decreased overbank flood frequency and duration.
The altered hydrologic regime affects four major characteristics
of this fluvial ecosystem; (1) reduced interaction between the
River and wetlands which once were part of-the rivers floodplain;
(2) reduced salt flushing; (3) reduced alluvial sediment
deposition; (4) reduced recruitment events for cottonwood trees.
Each of these issues is discussed below.
(1) Reduced interaction between the Colorado River and
floodAlain. Overbank flooding occurs in the study area with
-flows of 40,000 cfs or greater. Historical-frequency of flows of
-this magnitude was once every 1.86 .years. .Presently, flood-
- frequency is closer to once per decade.- Reduction in the
frequency and duration of flooding has resulted in dissolution of
-one large.-river-wetland ecosystem and resulted in the creation of
.two distinct ecosystems which .are hydrologically isolated.' The
Colorado River ecosystem including-its bed and .bars is
hydrologically driven by its watershed in the Rocky Mountains.
The Moab .wetlands are hydrologically driven by Mill Creek
watershed waters from the, La Sal Mountains near Moab and their ~`'
application to-field for irrigation, as well as the discharge of
groundwaters from the Wingate and Paradox Formations. Today, the
Moab wetlands are supported totally by water of local origin.
This water is .tributary. to the. Colorado River, and periodically
the Colorado-floods through-these wetlands, but these-are rare
events precipitated by some of the largest snowpacks on record
whose melting exceeded the capacity of the regions reservoirs.
In the past there was biennial-interaction between these-two
ecosystems, and adult Colorado River fishes, as well as drifting
larvae, had ample opportunity to-move from the River during high
stage, into the Moab wetlands. where refuge in the numerous ponds
of wetland communities was available. Historical air photo
interpretation leads us to believe that all Moab wetlands are.-
natural, and irrigation has had no significant measurable effect
on their overall acreage or characteristics.
Historically,. Colorado River fishes-could have moved back to
the River as stage declined, or they could have survived the
summer and winter in these ponds (which are up to 5 feet-deep,
contained appreciable invertebrate and small fish communities,
.and relatively-high DO concentrations) for one or more years, and-
be flushed back into the-River during the next flood event which.
had a frequency of 1 out of every 1.86 years. In addition, high.
flow ,years on the Colorado River also were high precipitation.
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