on 



1.4 The Mississippi Sound 



The Mississippi Sound and adjacent areas (Figure 1.2) is a regi 

 receiving greater attention due to increasing utilization of its resources, 

 including the dredging of shipping channels and the disposal of dredged 

 materials. A study of the area was Initiated by the U.S. Army Corps of 

 Engineers in 1977 to determine "whether the present and proposed dredged 

 material disposal methods for maintenance and construction should be modified 

 in any way at this time in the interest of economic efficiency and 

 environmental quality" (USAEMB, 1979). 



Extensive effort was made to summarize the various resources and economy 

 of the study area in an attempt to define the "without condition" to allow 

 impact assessment of alternatives. However, past studies on the most vital 

 resource - the hydrologic resource - of the study area appeared to be rather 

 limited, generally qualitative, and oftentimes resulted from scattered and 

 unrelated efforts. It was hence recognized that "much research is required 

 before a thorough picture of the local water mass dynamics is available" 

 (USAEMB, 1979). 



A recent study (Outlaw, 1981) of tidal data indicates that 01 

 (period=25.82 hours) and Kl (period=23.94 hours) are the predominant tidal 

 constituents in the study area with mean amplitude of both constituents near 

 15 cm. The tides in the entire Gulf of Mexico have been studied numerically 

 by Reid and Whitaker (1981). Using a 0.25° grid spacing, their model covers 

 the study area with only 9 grid points along the east-west direction and 5 

 points along the north-south direction. Schmalz (1982) studied the tidal 

 currents within the study area by means of a two-dimensional numerical model. 

 Despite a few studies in the past (Eleuterius, 1973; 1976; Gaul, 1967; 

 Christmas, 1973), little is known about the wind-driven currents and 

 density-driven currents in the study area. Knowledge about the bottom 

 currents is particularly lacking. Field studies indicated that an appreciable 

 horizontal salinity gradient may sometimes exist in the study area. 



There have been a few previous modeling efforts for the overall 

 circulation of the Gulf of Mexico. Baer, et al. (1968) first attempted to 

 compute the Gulf circulation patterns while excluding all topographical 



