Adopt A Beach:
Long Term Monitoring of Camping Beaches in Grand Canyon
Executive Summary of Results for Years 1996 - 2003
Introduction and Methods
The Adopt-a-Beach (AAB) program has completed its eighth year as a study
that monitors camping beaches in Grand Canyon. This program, sponsored
by Grand Canyon River Guides, Inc., is implemented by a 100% volunteer
force of river guides, scientists, and NPS personnel. Results are submitted
to various agencies such as the Cultural Resources Program of the Grand
Canyon Monitoring and Research Center (GCMRC). Results are also presented
to the Adaptive Management Program so that private and commercial recreational
interests are represented as stakeholders in Colorado River management
as reported to the Secretary of the Interior.
Methods implement repeat photography and observational comments that
document the condition of a selected set of Grand Canyon camping beaches
from April through October of each year. The selected beaches lie within
three critical reaches (Marble Canyon, Upper Granite Gorge and Muav Gorge)
of the river corridor. A critical reach is defined as an extended area
in which camping beaches are sparse, small, and/or in high demand. Two
recently added critical reaches (Glen Canyon and Lower Granite Gorge)
will also help in understanding long term erosion and system-wide sediment
distribution.
The program assesses visible change to beaches resulting from changing
regulated-flow regimes, rainfall, wind, and human impacts. Volunteers
for this program are unique in that they run the Colorado River many times
in one season, and they are able to provide sets of repeat photographs
for each study beach. To date, guides have produced over 1500 repeat photographs
and associated field sheets having recorded the sequential condition of
beaches throughout the commercial boating season, year after year. Research
results include total change to beaches after being impacted by certain
flow regimes, longevity of the 1996 beach/habitat building flow (BHBF)
deposits, change to individual beaches between monitoring seasons, and
primary and secondary processes that cause change in camping beach area
and quality.
Results and General Conclusions
Results of this study since 1996 show that beaches have continued to decrease
in size, system-wide even after the High Maintenance Flows (HMF) of year
2000 and the Winter High Fluctuating Flows (WHFF) of 2003. Over years
1996-1999, the net effect of controlled flow releases from Glen Canyon
Dam resulted in the continued winnowing of beachfronts, cutbank retreat,
and loss of camping area. The highest number of beaches showing negative
impacts from fluctuating flows were reported in 1997, at which time flows
reached a maximum of 27,000 cfs. Erosion to beaches through years 1998-1999
continued, but effects were not as profound. This decreased magnitude
of change through the years since 1996 reflects two geomorphic processes:
(1) the increased stability of beach fronts as they attain an angle of
repose, and (2) decreased amounts of sediment that can be eroded from
beaches. By fall 2001, most beaches that had initially gained area from
the HMFs of 2000 had returned to their 1999 condition. These conditions
persist today.
Many factors are contributing to long-term erosion of these beaches.
Primarily, erosion from medium fluctuating flows that contain low sediment
concentrations resulted in conditions that are similar to those before
the BHBF of 1996. Secondary processes contributing to erosion are listed
here and are ranked according to magnitude of impact: (1) gullying and
flash-flooding from rainfall; (2) beachfront erosion from campers; and
(3) wind deflation. Some recreational area loss to is due to encroachment
of vegetation, mostly tamarisk.
Campsite area and quality can be greatly enhanced by implementing BHBFs
well above power plant capacity, given there is available sediment inputs
from the Paria and/or Little Colorado Rivers. Over 80% of guides agreed
that camping (useable space and quality) had improved dramatically during
the Low Steady Summer Flows (LSSF) that followed the spring HMF of 2000.
Moreover, camps that would normally be under water became available for
consistent use. By spring 2001, most guides reported worse camping conditions.
This is attributed to relatively higher fluctuating flow zones on beaches,
rendering lower camping areas difficult to use, and creating eroded beachfronts
that presently expose rocks. Lack of a lower camping area will inevitably
force camping and recreation into higher zones and into the more fragile
xeric desert zone where many archeological sites are located.
The results of 8 years from this monitoring program show that the BHBF
of 1996 was the most beneficial management action for replenishing and
rebuilding beaches for campsite use. All other subsequent test flows produced
small new deposits that only lasted for 7-12 months, at most. These results
suggest that any newly deposited sand transported within power plant capacity
flows will be quickly eroded if followed by medium to high fluctuating
flows. This was evidenced by 3 events: (1) High flows (the high of about
27,000 cfs) following the 1996 BHBF eroded much of the new deposit at
all beach sites through the summer of 1997; (2) Medium fluctuating flows
following the fall HMF of 1997 stripped away the new deposit entirely
by spring 1998; and (3) Medium fluctuating flows following the fall HMF
of 2000 eroded most of the new deposit by spring 2001. To date, less than
30% of beaches show evidence of high-elevation sand (above 30,000 cfs
line) deposited by the 1996 BHBF.
Annual implementation of HMFs in spring and in fall would help preserve
camping beaches by maintaining the beachfront. The WHFF (5,000-20,000
cfs) of 2003 has been the least damaging flow, as beaches did not lose
as much beach area over the winter period compared to other winter periods
in previous years. However, WHFFs should not be substituted for beach
building and beach maintenance flows. A regimen of BHBFs that exceed power
plant capacity followed by low fluctuating flows are needed periodically
to rebuild campsite areas above the 30,000 cfs line. However, future BHBFs
need to have enough sediment in the system so as to preserve Marble Canyon
beaches and lessen impacts on lower beach areas (below the 20,000 cfs
line) systemwide.
For questions or comments please contact
Kate Thompson or Lynn Hamilton
Grand Canyon River Guides, Inc., Flagstaff, Arizona
(928) 773-1075.
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