199293, and 0.0 to 9.8 m during the summer of
ERF system is extremely complex, with multiple
1993. Two gully headwalls are advancing at a rate
internal parameters that vary daily, seasonally,
sufficient to cause increased drainage of ponds
and annually and with long-term external con-
within the next 1015 years if the 1993 rates are
trols. The natural system is governed by a high
characteristic.
tidal range, glacial river influences, large sediment
influx from two distinct sources, and a subarctic
coastal climate. In addition ERF is located within
Lawson, D.E., S.R. Bigl, L.E. Hunter, B.M.
Nadeau, P.B. Weyrick, and J.H. Bodette (1995)
an active earthquake zone that increases the
Physical system dynamics, WP fate and trans-
potential for rapid and unpredictable physical
port, remediation and restoration, Eagle River
changes in the future. The use of ERF as an artillery
Flats, Ft. Richardson, Alaska. In Interagency
impact range has also produced explosion craters,
expanded site investigation: Evaluation of white phos-
which have caused physical changes to the terrain,
phorus contamination and potential treatability at
hydrology, and surface drainage.
Eagle River Flats, Alaska (C.H. Racine and D. Cate,
Ed.). CRREL Contract Report to U.S. Army,
Tides
Alaska, Directorate of Public Works, FY94 Final
The elevation and duration of tidal inundation
Report, p. 53186.
affect sedimentation. Tidal flooding of the Bread
This study analyzes the physical processes of
Truck, C Pond, A, and Racine Island Areas is
erosion, sedimentation, and sediment transport,
enhanced by the discharge of the glacially fed
the factors controlling their activity, and the physi-
Eagle River, with its timing, peak height, and
cal transport of WP within ERF. Potential physical
duration affected by seasonal peaks in meltwater
system responses to natural or anthropogenic
discharge and precipitation in the river's water-
remedial measures, and the potential effects of
shed. In contrast, tidal inundation is related to tide
the physical system on proposed remedial meas-
height in gullies closer to the coast. Similarly, the
ures, are also discussed. Our investigations of the
direction and velocity of the wind across ERF pre-
physical system over the past 3 years have signif-
ceding and during tidal inundation may either
icantly improved knowledge of the processes
enhance or reduce the height and duration of
actively changing ERF and determining the flux
inundation. Storm-driven water masses in Cook
of sediment and water within the system.
Inlet may have the same effect on flood height in
Tidal height fluctuations were measured in
Knik Arm. Limited data indicate ice and snow
1994 in concert with water level changes in eight
cover can enhance the height and duration of
major tidal gullies and in the Eagle River where it
flooding as well.
discharges into ERF. These measurements define
A comparison of water level variations at the
the timing and distribution of flood and ebb
heads of eight gullies across ERF and in the Eagle
waters and qualitatively assess the contribution
River showed a 20- to 40-mm delay in the timing
of the Eagle River discharge to flooding. Sus-
of the peak tidal flood height relative to that pre-
pended sediment concentrations were also meas-
dicted at Anchorage by tide charts. When the pre-
ured in the Eagle River, gullies draining the
dicted tide height is sufficiently high to flood part
or all of ERF, the actual peak elevation exceeds that
ponds and mudflats, and Knik Arm to define the
height. Flood height is generally greater than the
contribution of these sediment sources to pond
Anchorage datum by 0.5 m or more, with the
and mudflat sedimentation. Salinity, tempera-
amount dependent on the volume of glacial melt-
ture, dissolved oxygen (DO), pH, and turbidity
water in the Eagle River and possibly Knik Arm.
were measured to assess the contributions of tidal
or riverine water masses to flood and ebb cycle
The general increase may be caused by the con-
white phosphorus (WP) sedimentation, trans-
striction in Knik Arm south of ERF.
port, and erosion. Hydrologic parameters,
including drainage pattern, channel gradients,
Suspended solids
channel cross sections, and flow velocity, were
The total suspended solids (TSS), or suspended
also analyzed to calculate ebb discharge and sed-
sediment concentrations, in waters of ERF vary
iment and WP particle transport rates, and to
with tidal stage, location, source, and season. The
model sediment and water flux. Over 200 sedi-
glacially fed Eagle River varies seasonally from
ment samples were collected and analyzed for
peak TSS values of 100700 mg/L between break-
WP.
up in May and freezeup in October. Two seasonal
The results of our studies have shown that the
highs occurred in 1994, the first in early June
47
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