Variation of Results During One Tidal Cycle 



The surface displacement contours at 6-hour intervals throughout the 

 tidal cycle are shown in Figure 5.18. At the beginning of the tidal cycle, 

 i.e., 72 hours after the initiation of the simulation on 1 Sept. 1980, surface 

 displacements in the area vary from -9 cm within the western end of the 

 Mississippi Sound to about 12 cm along the southern open boundary. Variation 

 in surface displacement along the southern boundary is approximately 4 cm, 

 with an along shore pressure gradient directed to the west. Six hours later, 

 at 78 hours, surface displacements within the Mississippi Sound have reached a 

 peak value on the order of 20 cm. Along the southern open boundary, however, 

 surface displacements have dropped to about 4 cm. Another six hours later, at 

 84 hours, the situation is almost reversed from that at 72 hours. Surface 

 displacements along the open boundary are on the order of -12 cm. Within the 

 western end of the Mississippi Sound and Lake Borgne, surface displacements 

 are on the order of 12 cm. It is also interesting to note that the 

 along-shore pressure gradient is now directed towards the East. At 90 hours, 

 the entire study area has negative surface displacements, ranging from -4 to 

 -24 cm. At the end of the tidal cycle, 96 hours, the situation is rather 

 similar to that at 72 hours. 



The horizontal velocities near the surface and near the bottom, at 

 six-hour intervals, are shown in Figures 5.19 through 5.23. At 72 hours, 

 near-surface currents on the order of 63 cm/sec exist within the tidal inlets. 

 The near-bottom currents, however, are smaller by more than 20%. Currents 

 through the tidal inlets are all directed into the Mississippi Sound. Six 

 hours later, at 78 hours, the currents have decreased by approximately 50%. 

 Currents within the western end of the Mississippi Sound, at this instant of 

 time, have become relatively stronger compared to currents in other areas. 

 Although most tidal inlets show flow into the Sound, outflows are found in 

 Petit Bois Pass and Dog Key Pass. At 84 hours, strong currents on the order 

 of 70 cm/sec are directed out of the Sound. Near-bottom currents are smaller 

 than the near-surface currents by approximately 30%, Little flow exists 

 within the western end of the Sound. At 90 hours, currents are again 

 decreased in magnitude. It is interesting to note that flow is directed into 

 the Sound through the eastern and central tidal inlets, while directed out of 



93 



