Geology Reference
In-Depth Information
(a)
Significant wave heights
0.8
0.6
0.4
0.2
0
(b)
Northern component of current velocities at the bottom
200
100
0
−
100
−
200
(c)
Average windspeeds and maximum gusts
25
20
Average winds
Gusts
15
10
5
0
4
6
8
10
12
14
16
18
20
22
24
26
28
30
1
3
Date (3 August through 4 September 2005)
Fig. 10.
Wave gauge measurements (top) compared with the tidal velocities (middle) and atmospheric data from the NOAA
buoy (bottom). The wave gauge was located between the reef and the apex of an ebb tidal delta (dark blue in Fig. 1).
The ADCP was located in the inlet between Jack's Cay and Carter's Cay (ADCP1 in Fig. 1). The wave height increases in
response to Hurricane Katrina (red dashed box, Fig. 9) prior to the decrease in wind speeds. The waves in this region,
however, generally remain between 0.2 and 0.4 m high.
were only slightly modifi ed from the rest of the
tidal cycle's magnitudes. From the simplifi ed
storm wave calculations described previously,
this corresponds to conditions analogous to the
12 m s
1
winds, which may produce waves
that could move sediment in waters shallower
than 4.8 m. Therefore, the combination of the cur-
rents and waves produced by this storm could
have impacted the tidal deltas, albeit for a short
time period, and changed them somewhat.
In comparison, the daily bottom tidal currents
of the tidal deltas approach and can exceed 1 m s
1
in some areas (Fig. 10), much greater than the
threshold velocity of sediment entrainment of
the average diameter (0.5 mm) for ooids found
in the tidal delta region (0.26 m s
1
). Although
the velocities produced during a storm may be
greater than these tidal velocities, they are short-
lived. In contrast, tides move in and out, day
after day, reapplying the same forces to the sys-
tem. Therefore, although sediment may be trans-
ported and redeposited during storms and periods
of higher-than-average velocities, the duration of
storms may not be enough for signifi cant mor-
phological adjustments. Likewise, based on our
continuing observations (described above) it is
