Tidal elevations are also influenced by the wind. An east wind tends to 

 lower elevations in the eastern part of the sound and increase tidal 

 elevations in the western part of the Sound. A west wind has the reverse 

 effect of increasing elevations in the east and lowering elevations in the 

 west. (U.S. Army Corps of Engineers 1983). 



Tidal current velocities in Mobile Bay average between 0.15 and 0.76 m/s 

 (0.5 and 2.5 ft/s) (O'Neil and Mettee 1982) Velocities in Mississippi Sound 

 wary from to .24 m/s (.8 fps). In general, peak velocities throughout the 

 Mississippi Sound will increase by 40% per one foot increase in the tidal 

 range (U.S. Corps Army of Engineers 1983). 



SALINITIES 



The salinity regime of Mobile Bay can vary from to 34 to 36 parts per 

 thousand (ppt). Individual locations within the bay may vary a great deal 

 due to interactive factors such as tidal regime, currents, river discharge, 

 rainfall, and velocity and direction of the wind. In deeper portions of the 

 bay vertical stratification (layering) may also occur. 



The most important factor influencing salinity in Mobile Bay is the 

 discharge of the Mobile River. During seasonal high-flow periods (February 

 through April), surface salinities are often less than 10 ppt in most of the 

 bay. During the low-flow period from July throuah December, surface 

 salinities increase, reaching 10 ppt in the northern portions of the bay and 

 20 ppt or more in the southern portions (U.S. Army Corps of Engineers 1983). 

 The seasonal surface salinities in Mobile Bay are mapped on the atlas sheets 

 and show these extremes. 



Higher salinities are found more in bottom water than in surface water. 

 This is especially true in the Mobile Ship Channel (Mobile quadrangle) which 

 allows the denser saltwater to extend as far as 23 mi up the Mobile River. 

 Stratification in Mobile Bay is most often present during the low-flow 

 periods of the Mobile River, and less pronounced during the river's high-flow 

 periods. Mixing of the waters in the bay appears to be retarded by the spoil 

 banks on either side of the ship channel , since they act as submerged 

 partitions (O'Neil and Mettee 1982). 



Perdido Bay shows many of the same characteristics as Mobile Bay except 

 that saltwater wedge intrusion is less pronounced and mixing is greater in 

 the lower part of the bay, reducing stratification (O'Neil and Mettee 1982). 



The Mississippi Sound (Biloxi quadrangle) has the highest salinities of 

 the three estuaries, reflecting the free connection with gulf water and small 

 inflow of fresh water. In addition, stratification is minor, with the 

 difference between surface and bottom salinity being only 2 ppt (Bault 1972). 



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