Based on these results, a preliminary estimate indicates the average flow 

 through the passes is approximately 1.8 x 10 CFS, which is very close to the 

 estimate by Escoffier (1978) as referenced in USAEMD (1979). It is also 

 interesting to note that the maximum shear stresses occur within the major 

 passes. Such high shear stresses, even in the absence of favorable wind 

 waves, may be capable of resuspending fine sediments in the area. 



The results at six hours later, although not shown here, indicate flow 

 through the tidal channels has increased and near-surface currents are on the 

 order of 30 cm/sec. The bottom shear stress has also become stronger. The 

 near-bottom horizontal velocities as a function of time are shown in 

 Figure 4.11 for three locations (see Figure 4.9) in the area. The phase 

 relationship between u and v at the deeper location (1=21, 0=28) is quite 

 different from that within the Sound. 



4.7 Wind-Driven Response in the Mississippi Sound-Idealized Basin 



Strong winds frequently exist in the study area. The winds in the Gulf 

 of Mexico are predominantly from the North in winter and South to Southeast in 

 the summer; however, winds are stronger in the winter from the West and the 

 Northwest and in the summer are not as strong but of equal strength in all 

 directions. The land winds are stronger in the winter but no direction is 

 dominant, and in the summer the strongest land winds are from the South to the 

 Southeast. Occasionally, hurricanes of destructive force hit the area. 

 Currents and water level induced by the strong winds can be much greater than 

 those induced by the tide and hence are of primary interest to us. 



2 

 Assume at t=0, a uniform wind stress of 3 dyne/cm (corresponds to a wind 



speed of about 10 m/sec) is applied over the entire surface area impulsively. 



We have computed the response of the region for four different cases: 



2 2 2 



(1) Tj^=+3 dyne/cm , (2) t =+3 dyne/cm , (3) \=-^ dyne/cm , and 



2 2 



(^) ^"^'^ dyne/cm . Constant A of 200 cm /sec and Cq of 0.04 were used in 

 the computations. 



Adiabatic boundary conditions are used along the open boundaries. 

 Although this does not allow us to include the effect of shelf waves into the 

 computation, the model can still simulate the local response of the study area 



68 



