7800

• UCREFRP Catalog Number: 7800
• Author: Burdick, B. D.
• Title: Conceptual Management Plan for Habitat Enhancement in Flooded Bottomlands, Gravel Pit at 29-5/8 Road, Colorado River Near Grand Junction, Colorado.
• USFW Year: 1994.
• USFW - Doc Type: \
• Copyright Material: NO

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the amount of lacustrine habitat should reduce the proliferation of non-native
piscivorous fishes while, at the same time, provide backwater habitat for
endangered fishes during spring runoff. Because the course of the river might
compromise the dike and wash out any back-fill added to the pond, the decision
was made to take a "wait-and-see" approach before committing resources to back-
fill the pond. At the downstream end of the pond, a portion of the dike would
be removed to construct a channel that would connect the pond to the river.
Stream Flows. Throughout the upper Colorado River basin dramatic physical
changes have been made to the riverine environment. Probably the most
significant change has been the alteration of natural flow regimes by water
development projects on the tributaries and mainstem rivers. Although many
private irrigation projects already existed, development of water storage in the
upper Colorado River basin began in earnest during the 1930's with the
construction of several projects by the Bureau of Reclamation. Reservoir
construction in the upper basin increased dramatically in the 1950's and 1960's
with the Colorado River Storage Project (CRSP). Regulated flows from high dams
and diversion structures upstream of historic bottomland areas remove water from
the river for municipal, industrial, and agricultural uses. These activities
have affected the main channel and, in some instances, eliminated-off-channel
habitats such as backwaters, embayments, and bottomlands as nursery areas for
some of the endangered fishes. The most noticeable change has been the reduction
in historic peak flows.
The "15-Mile Reach" of the Colorado River, where the 29-5/8 Road Gravel Pit
site is located, is influenced greatly by upstream water diversions. Osmundson
and Kaeding (1991) compared flow records from the historic or pre-water
development era (1902-1942) with the post-water development era. They calculated
that the mean peak flow in the "15-Mile Reach" of the Colorado River is now only
56% of the historic mean. The greatest loss of natural flows occurs during the
months of May (58%) and June (56%) that historically inundated the floodplain.
In essence, floodplains now are inundated less frequently, if at all. Prior to
1937, the annual peak flow at the State Line stream flow gage exceeded 30,000 cfs
81% of the time, and exceeded 40,000 cfs 56% of the time; in recent years (after
1965) peak flows exceeded 30,000 cfs 33% of the time, and exceeded 40,000 cfs
only eight per cent of the time (Figures 2 and 3). During the 16 years of
historic record, peak flows at the State Line gage were never less than 26,000
cfs. From 1966 to 1990, peak flows have been less than 26,000 cfs, or about 58%
of the time. Therefore, what has changed is the loss of the regular high-volume
years, which are important to inundating off-channel habitats in floodplains.
Although it would be prudent to implement recommended river flows that
would inundate floodplains in the spring during May and June to provide off-
channel habitat, necessary flows might not be available frequently enough to
benefit recovery of the endangered fishes. Notching old dikes at strategic
locations while providing some level of protection from flooding to private
property and structure may be another strategy to provide access into off-channel
habitats for various life stages of endangered fishes. The U. S. Army Corps of
Engineers was recently given jurisdictional authority to regulate excavation of
fill material in wetland areas and below ordinary high water in riverine reaches
where critical habitat has been designated for endangered fishes. In the future,
as a condition of being granted a 404 permit, gravel mining companies that create