9390

• UCREFRP Catalog Number: 9390
• Author: Webb, R. H., T. S. Melis and R. A. Valdez.
• Title: Observations of Environmental Change in Grand Canyon, Arizona.
• USFW Year: 2002.
• USFW - Doc Type: 02-4080,
• Copyright Material: NO

mouth of the Little Colorado River (mile 61.5); such a
run today is more difficult although possible at
discharges above 20,000 ft3/s in the Colorado River.
There are subtle implications to these
observations. The 1973 flood in the Little Colorado
River changed the bar at the mouth significantly;
Shoemaker specifically asked us to match Stephens'
1968 photograph to verify this. The debris flow out of
South Canyon (mile 31.6-R), which occurred between
1940 and 1965, could have added significantly to the
material in the debris bar opposite Vaseys Paradise
(mile 31.9). This relation between debris bars and the
parent debris fan represents another documented case
of the relation between debris flows and the course of
the Colorado River.

Driftwood

Before closure of Glen Canyon Dam in 1963,
fires were set by some Old Timers in the enormous
driftwood piles lining the river corridor. This activity
was undertaken at the request of the National Park
Service and the Bureau of Reclamation, who were
concerned about the effect of driftwood on navigation
in Lake Mead. These fires caused a considerable
reduction in the amount of dead biomass below the old
high-water zone. Driftwood accumulated over a
thousand years (Ferguson, 1971), and its destruction
over a few decades, represents a huge acceleration in
the release of nutrients into the atmosphere and into the
sands adjacent to the river.
The magnitude and number of fires set along the
river corridor by pre-dam river runners was large
(Table 3). The effects could be seen for years; for
example, signs of the 1940 fire at the mouth of Saddle
Canyon (mile 47.0-R) were still prominent in 1942.
The reduction in driftwood was substantial owing to
the deliberately set fires and subsequent use of
firewood for cooking fires. Rigg remembers seeing
huge piles of driftwood on every debris bar below Lava
Falls Rapid; now, there is little driftwood on these bars.
Many Old Timers indicate the decrease in driftwood is
one of the major changes in the river corridor. The
number of pre-dam fires, combined with the presence
of Glen Canyon Dam, may have been largely
responsible for the current state of depleted firewood in
the canyon.

Another contributing factor to the reduction in
driftwood could have been its use in campfires just
after closure of Glen Canyon Dam. During the first 15
years of river running on the regulated river, wood was
the primary fuel for cooking. It seems improbable that
the large piles of driftwood could have been
diminished by typical kitchen use, but Grua remembers
large piles that were depleted between 1969 and 1980.
As early as 1967, Cross II wrote about the abundance
of new driftwood introduced to the main channel
during the 1966 tributary floods, adding in his notes
that "firewood would not be a problem" during the
1967 river season. Nevills Reiff thought there was
more driftwood now than when she last was on the
river in 1972. She also felt the ban on summer wood
fires has had a major effect on increasing the amount of
driftwood, which now is added only during infrequent
tributary floods.

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Riparian and Desert Vegetation

Riparian vegetation is a highly valued resource
in the western United States owing to its high
productivity, diversity of species, and habitat for
wildlife. The Colorado River through Grand Canyon
had only sparse riparian vegetation before Glen
Canyon Dam (Turner and Karpiscak, 1980; Webb,
1996). Tamarisk,a non-native species, was introduced
to the western United States in the late 19th century and
spread through the Colorado River drainage (Johnson,
1991). Although Graf (1978) reported that tamarisk
spread upstream through Grand Canyon between 1910
and 1923, observations of the Old Timers, combined
with repeat photography and diaries, suggests
otherwise.

Riparian Vegetation

All the Old Timers observed the huge increase in
riparian vegetation along the Colorado River. The
change was considered both good and bad: good for
shade and wildlife, bad for environmental aesthetics
and camping space. The Old Timers recognized
tamarisk as the major contributor to the increase. A
excellent example of the increase in tamarisk is at
Lee's Ferry. Although Graf (1978) claims that tamarisk
is visible in 1923 photographs at this site, we see no
evidence oftamarisk in historical photographs of Lee's
Ferry or Grand Canyon (including those examined by

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18 OBSERVATIONS OF ENVIRONMENTAL CHANGE IN GRAND CANYON