Table 11. Characteristic temperature and salinity of Knik Arm and Eagle River source
waters during flood and ebb portions of selected flooding events.
Knik Arm
Eagle River
Temperature (C)
Temperature (C)
Salinity (ppt)
Salinity (ppt)
Date
Flood
Ebb
Flood
Ebb
Flood
Ebb
Flood
Ebb
May
25
8.27.5
7.57.8
--
--
6.26.5
6.58.0
0.1
0.1
26
8.78.0
8.08.3
15.516.3
7.17.2
7.28.5
0.1
0.1
September
78
11.412.4
12.412.2
5.86.2
5.57
5.76.2
--
--
89
11.512.5
12.512.2
5.96.5
7.37.0
7.06.8
0.1
0.1
October
56
8.28.9
8.98.8
6.36.1
6.16.2
0.1
0.1
67
8.38.8
8.88.7
8.210.0
10.09.9
6.25.8
5.85.5
0.1
0.1
78
8.08.6
8.68.4
5.04.5
4.54.0
0.1
0.1
November
34
0.81.6
1.61.5
11.212.7
12.712.6
--
--
--
--
45
0.71.7
1.71.3
11.413.0
13.012.8
--
--
--
--
56
0.41.3
1.31.0
11.613.0
13.012.9
--
--
--
--
Table 12. Gross sedimentation rates. Measurements for seasons
through winter 19931994 are from transect lines 112 only, Sum-
mer 1994 measurements from lines 124.
Range (mm)
Morphological unit
Sum 92
Win 9293
Sum 93 Win 9394
Sum 94
Levee
16
112
06
011
015
Vegetated mudflat
16
116
114
121
130
Unvegetated mudflat
113
712
18
610
117
Pond plate
14
828
626
217
121
Pond cup
29
826
619
113
220
Marsh
ND
ND
ND
ND
120
Gully
177
2033*
019
016
119
* Based on small sample size.
The Mortar Gully record (Fig. 31) displays the
diurnally, marking periods of tidal inundations
expected pattern of decreasing temperatures from
(Fig. 33). During fall flooding (68 September, 58
mid-August to mid-October as air temperatures
October), the salinity increase is longer as the
drop. This decrease in temperature, coupled with
higher flooding levels cause Knik Arm water to
increases in salinity, causes the water to become
remain impounded in the northernmost section
denser, thereby increasing its capacity to trans-
of Area A when freshwater spring discharge is
port sediment. Salinity changes at Mortar Gully
apparently lower.
are cyclic, opposite to the tidal flooding sequence,
becoming more saline between flooding periods.
Central sites
This saline condition is likely caused by the dis-
Hydrostation sites in the central area of the
continued exchange of water between Knik Arm
Flats monitor gullies that hydrologically link
and the ponds, allowing the salinity to increase in
ponds to the Eagle River. Observed patterns are
the ponds and the plunge pools at the gully heads
cyclic and generally consistent from mid-summer
through evaporation and stagnation. During
to fall. Temperature decreases steadily through
flooding, the salinity drops to the relatively low
the period, while salinity levels during floods in-
levels of Knik Arm water.
crease in response to the decreasing glacial melt-
Spring Gully, with significant freshwater in-
water input. Increased salinity between flooding
put, maintains salinity levels near zero ppt when
events in Parachute and Tanker gullies means
tides are low, but has increasing salinity semi-
that their waters become stagnant and evaporate.
29
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