6
G
Coastal East
D
7
8
F
C/D
5
Gullies
Ponds
Areas
9
E
10
BT
Clunie Pt.
11
D
Clunie
C
1--Racine
A--Racine
B--B-area
Coastal West
4
reek
12
2--B-Gully
B--C-Pond
RI--Racine Island
3
B
EOD
Pad
A
3--Parachute
C--Lawson's
C--C-area
C
2
4--In-Between
D--Bread Truck
EOD Pad
H
RI A
5--Bread Truck
E--C/D-Pond
C/D--C/D-area
N
1
6--Coastal 1
F--Pond Beyond
BT--Bread Truck
13
RB Bravo
t.
7--Mortar
G--D-Pond
D--D-area
ridge
8--Coastal 4
H--A-Pond
Coastal East
B
9--Coastal 5
I--B-Pond
Coastal West
I
10--Coastal 6
A--A-area
0
500
1000 m
11--Coastal 7
12--Tanker
13--Otter Creek
Figure 5. Locations of gullies, ponds and areas.
enhanced seasonally by the discharge of the gla-
indicating that deposition here is mainly derived
cially fed Eagle River, particularly by snowmelt
from overbank flooding of the river.
and precipitation in the river's watershed (Fig 5).
Suspended sediment concentrations measured
In contrast, inundation along the coast is a func-
in 1994 in the Eagle River, tidal gullies draining
tion of tidal height, which may be influenced by
the ponds and mudflats, and Knik Arm show that
the direction and velocity of the wind, ice cover
most of the sediment is derived from Knik Arm
and storm-driven surges in Knik Arm.
tidal waters (Lawson et al. 1996). The Total Sus-
pended Solids (TSS) in the waters of ERF vary
Tidal current measurements indicate that ve-
with tidal stage, location, source and season. TSS
locities are higher during ebb than during flood,
values in the glacially fed Eagle River vary sea-
and thus sediment transport and channel erosion
are potentially greatest during ebb (Lawson et al.
sonally from peaks of 100700 mg/L between
breakup in May and freezeup in October. Appar-
1996). Peak velocities within gullies ranged from
ently, there are two seasonal highs each year, the
about 0.8 to 1.9 m/s in 1994 and varied from site
first during snowmelt runoff and the second dur-
to site and with the elevation of tidal flooding.
ing the peak glacial melt season. In contrast, TSS
The velocity variations reflect differences in gully
values of Knik Arm water range from about 1000
width, depth, roughness and network configura-
to 2800 mg/L from May to October. The high TSS
tion.
values of Knik Arm reflect its source from large
The Eagle River provides access for tidal wa-
glacial rivers (e.g., Susitna, Knik and Matanuska),
ters to inundate the innermost reaches of the Flats.
High tides increase river stage by tidal damming
which have higher sediment discharges than the
and reversing flow in the river. Sedimentation in
Eagle River. During a tidal cycle, TSS measure-
the northern two-thirds of ERF is tidally domi-
ments at gully sites increase steadily through the
nated, whereas the southern one-third appears to
flooding tide and decrease at a slower rate during
be river dominated. Tidally dominated sedimen-
the ebb. Seasonally, TSS values in gully and Knik
tation ranges from several millimeters per year
Arm waters increase from spring to fall; the cause
on levees, to 1015 mm/year on mudflats, and up
of this increase is unknown.
to 2040 mm/year in ponds. Sedimentation has
Gullies are actively extending into the mudflats
formed an alluvial fan at the head of ERF (Fig. 6),
and ponds in the Bread Truck, C, A, D and C/D
7
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