Geology Reference
In-Depth Information
Fig. 5. (a-d) Sequential aerial
photographs (1928-1953-1964) and
satellite image (2005-Ikonos © GeoEye)
of the East Cape Canal area. Shoreline
erosion occurred between 1928-1953
and 1953 and 1964, interpreted to be the
direct result of hurricanes. 1928 shore-
line has moved inland approximately
180 m. Ponds on the 1928 aerial pho-
tograph have fi lled up and mangroves
cap the intertidal mudfl ats at present.
Hidden Creek is connected to Florida
Bay by 1953, East Side Creek fi rst
appears on 1964 aerial photograph.
as well as directly measured in combination with
salinity with a conductivity-temperature-depth
(CTD) recorder (resolution is 0.02 psu for salinity
and 0.03 m for water level).
The amount of suspended sediment in the water
column was measured with a turbidity sensor.
A total of 65 in situ water samples were collected
for validation analysis between turbidity sensor-
derived values and in situ measured values of sus-
pended sediment. The correlation coeffi cient is
0.83 and there is a 95% confi dence level that the
compared values are correlated.
the interior freshwater marshes of southern Cape
Sable, and between Cape Sable and the Gulf of
Mexico and Florida Bay. Three canals are impor-
tant for this study: ECC, HSC and MCC (Fig. 1).
These canals cut through the marl ridge and
connect the interior freshwater marsh with the
coastal lagoon, Lake Ingraham and Florida Bay.
Before canal construction, the water depth in
the enclosed fresh- to brackish-water lagoon was
1-1.5 m (Gebelein, 1977). Initially, the canals were
less than 4 m wide and did not reach limestone
bedrock (Davis, 1972). The volume of water pass-
ing through the canals was small at fi rst, and in
fact, a hurricane in 1935 choked MCC with trees
and overwash sediments (Simons & Ogden, 1998).
However, tidal fl ow through ECC and MCC caused
a continual and persistent deepening and widen-
ing in those channels at rates of 60 and 120 cm
per year respectively (Davis, 1972), widening
that continues to the present (Fig. 5d). Presently
ECC measures 70 m in width, MCC 130 m in
width, and both canals cut to the Pleistocene
limestone surface at 3.5 m depth. Two natu-
ral creeks, Hidden Creek and East Side Creek
(Fig. 5d) have also been widening steadily. HC
naturally connected Florida Bay to the Southern
Lakes and Lake Ingraham in 1950 and has since
been widening at a rate of 60 cm per year (Davis,
1972) and is now 35 m wide.
RESULTS
Historical stresses to study area
Cape Sable has undergone large geomorpho-
logical, ecological and sedimentological changes
over the past 80 years, caused by a combination
of factors: (1) small but signifi cant human modifi -
cations, mainly the dredging of narrow canals in
the 1920s, (2) major hurricanes and (3) historical
relative rise in sea level.
Canals
Through the early to mid-1920s, a series of dredg-
ing projects created a network of canals across
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