ecological characterization atlas of coastal alabama - Data Center

consisting of a wedge of salt water, move upstream in Perdido Bay during a
flood tide . These upstream currents encounter the usual downstream currents
and create counterclockwise bottom currents in the upper basin of Perdido
Bay . Figures 18 and 19 show flood- and ebb-tide current patterns in Perdido
B ay .
The velocities of flood t-l~es in Perdido Bay have been measured by the
U .S . Army Corps of Engineers to average 0 .8 m/s (2 .5 ft/s) and reach a maxium
of 1 .2 m/s (4 .0 ft/s) . Ebb-tide velocities average 0 .6 m/s (2 .0 ft/s) and
reach a maximum of 0 .7 m/s (2 .3 ft/s) .
Mobile Bay and Mississippi Sound
Information on current patterns in Mob ;le Bay has been collected by
several researchers, using both field observations and computer modeling .
Austi n(1954 ) was the fi rst to map fl ood and ebb ti de ci rc ul ati on patterns i n
Mobile Bay . Story, et al . (1974) traced circulation patterns in a portion of
Mobile Bay by the use of fluorescent dye markers . Several publications by
Schroeder (1976, 1977, 1979a, 1979b) discuss circulation patterns in Mobile
Bay . His studies involved current data collected while anchored, drogue
studies, and inferring circulation patterns from salinity patterns .
Computer models of Mobile Bay have been developed by April et al . (1976),
April and Raney (1979), Pitts and Farmer (1976), and Gaume et al . (1978) .
The major difference between these models is how they model the openings of
the bay, which are complicated by Dauphin and Little Dauphin Islands (Biloxi
quadrangle) (0'Neil and Mettee 1982) . Figures 20 and 21 show flood and ebb
tide current patterns in Mobile Bay as predicted by April et al . (1976) .
The general circulation pattern in Mississippi Sound is induced by the
tides but wind has a significant effect on the currents . Horn Island Pass
(Biloxi quadrangle) is the natural dividing point for tidal currents in the
Mississippi Sound . During flood tide the currents bifurcate in the Horn
Island Pass area and flow westward and eastward . From Horn Island pass to
Mobile Bay, currents flow in through the passes and eastward on the flood
tide, then westward and out during ebb-tide (U .S . Army Corps of Engineers
1983) .
Recent numerical modeling by the U .S . Corps of Engineers (1983) on
current patterns in Mobile Bay and Mississippi Sound indicate that wind has a
significant effect on circulation patterns . East and west winds have a
pronounced effect with north and south winds having minimal effects .
Variance in wind velocities also exerted pronounced effects on circulation
patterns (U .S . Corps of Engineers 1983) .
The effect of the wind on the tidal currents is mainly to superimpose a
wind induced current on the Sound that shifts the bifurcation of the currents
either toward the east or west . The eastward or westward movement of the
current depends upon the di rection of the wi nd and whether the ti de i s in ebb
or flood . An east wind component induces a westward current in the Sound,
which causes a shift in the current dividing point to the east during floodtide
and to the west on the ebb-tide . Winds with a component from the west
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