7423

• UCREFRP Catalog Number: 7423
• Author: U.S. Bureau of Reclamation.
• Title: Glen Canyon Environmental Studies Draft Report, September 1987.
• USFW Year: 1987.
• USFW - Doc Type: Washington, D.C.
• Copyright Material: NO

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
"I
I

cfs, whereas the Peaking Power Program would raise peak
releases to about 40,000 cfs. Adverse public reaction
to the Peaking Power proposal led to its termination in
1980.

BaR published an environmental assessment in December,
1982, of the impacts of the Uprate and Rewind Program.
No significant impact of increasing the peak powerplant
capacity from 31,500 to 33,100 cfs was found, but the
close association in time with the Peaking Power study
tended to blur the separate issues in the pUblic's mind
and again provided a focus for existing concerns about
impacts of current operations.

The BaR proceeded with the Uprate and Rewind Program
for the generators at Glen Canyon, but agreed not to
use the increased powerplant capacity until a more
comprehensive study of the impacts of historic and
current dam operations was completed. The effect of
fluctuating releases on the environment and recreation
was therefore a major focus for the GCES.

Larqe Releases From Glen Canyon Dam Are More,Common
since The Filling Of Lake Powell And Are A Cause
Of Public Concern

From the start of flow regulation in 1963 until the
filling of Lake Powell in 1980, releases generally
stayed between l,OOO cfs and 3l,500 cfs. Higher re-
leases were very rare. Although the dam produced
fluctuating flows which recreationists found undesir-
able, it also eliminated the very large spring and
summer floods which had annually scoured Glen and Grand
Canyons with peak flows of up to 300,000 cfs. The
elimination of annual flooding allowed a much more di-
verse and extensive riparian vegetative and wildlife
community to colonize the old "flood zone" along the
river.

However, when Lake Powell filled in 1980, the capacity
of the reservoir to store unusually high spring runoff
was severely reduced, leading to the current situation
in which "flood" releases (over 31,500 cfs) are more
common. Concerns were raised over the effect of these
flood releases on sediment deposits and vegetation in
the river corridor, aquatic and terrestrial wildlife,

11