Line 12
e2
Line 10
Lin
1
e1
Lin
Line 3
Line 5
Line 7
Line 4
Lin
e9
18
Lin
Line 8
e
e
Li
Lin
19
ne
Line 6
N
20
3
ine 2
L
Line 24
P
Eagle River
I ermanent Pond
D termittent Pond
n
T rainage Gully
Line 22
ransect Line
0
500 m
Figure 9. Mudflat sedimentation transect locations.
between these two readings defines the net sedi-
surveyed using an electronic theodolite. Grab
mentation (or erosion) rate. Rates were measured
samples of surface sediment (to 5 cm depth) were
in July, August and September 1992 following
taken at each survey point along the transects,
each monthly period of tidal flooding, while sea-
and their grain size distributions were analyzed
sonal rates were measured in May and September
using standard sieving and hydrometer tech-
1993, 1994 and 1995.
niques. These data delineated textural trends in
Sedimentation on levee and mudflat surfaces
surface materials and the relative importance of
was monitored by spraying an area (~30 30 cm)
tidal and river sediment sources to sedimentation
on the ground surface with pavement-marking
and landform development (Lawson and Brockett
paint and locating the corners of this area with
1993).
wire survey flags (see also Vince and Snow 1984).
Sedimentation stakes were used to measure
Paint was applied at certain sites in June and
surface aggradation or erosion on transects where
August 1992, August 1993, and MayJune 1994.
the surface was wet or standing water was tem-
Net accumulation was measured by cutting and
porarily present (Fig. 10). These stakes consisted
of a rod and a square, rigid plate (about 7 cm2)
removing a block of sediment with a putty knife
or spatula (Fig. 11). The thickness of sediment
that slides freely on it, following Ovenshine et al.
above the paint layer was then measured to the
(1976a,b) in Turnagain Arm, Alaska. Erosion depth
nearest 0.5 mm. In contrast to the sedimentation
is defined by the increase in distance between the
stakes that were commonly broken or removed
top of the rod and the top of the plate, as mea-
by ice during winter, the wire flags and buried
sured periodically to the nearest 0.5 mm. The
paint horizons enabled us to acquire a continuous
amount of accretion is the thickness of sediment
record of net sedimentation rates.
deposited on the plate surface. The difference
14
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