7.4 Wave Effect on Sediment Dispersion 



Wave Modeling 



In addition to the tidal currents and wind-driven currents, bottom 

 orbital currents induced by wind waves in the Sound can cause entrainment of 

 the bottom sediments. The wind waves in the Sound have been studied by using 

 a spectral wave hindcasting model (Resio and Vincent, 1977) modified for 

 shallow water environment. Basically, wave energy in the Sound is assumed to 

 be derived completely from within the system. While some energy may actually 

 come into the Sound from the Gulf through the tidal inlets, this appears to be 

 a reasonable assumption since most of the incoming waves may break outside the 

 barrier islands before entering the Sound. Some results are presented in the 

 fol lowing. 



Figure 7.13 shows the area of wave study containing locations of the 

 various stations. Wind data during September 1980 were recorded at four 

 meteorological stations (MET 1, MET 2, MET 3, and MET 4) in the area. Two 

 types of simulations were performed. The first simulation combines the hourly 

 winds at these stations to compute an average wind for the entire Sound. The 

 second simulation takes into account the variation of wind over the water and 

 computes a wind velocity for each of the numeric wave stations. The second 

 simulation generally results in somewhat higher waves and stronger bottom 

 orbital currents than the first simulation, but contains more uncertainty with 

 regard to the nature of over-water wind variation. For simplicity, we will 

 only present results obtained with the uniform wind. 



Wave Climate and Bottom Stresses During 9/20/80 to 9/25/80 



The detailed wind velocity during 20 September through 26 September 1980 

 is shown in the stick diagram, Figure 7.14. Relatively mild winds are 

 generally from the southeast except during a few hour period on September 4. 

 Significant heights at stations 8, 10, and 17 are shown in Figure 7.15 and are 

 generally less than 1 ft. Wave periods at all the stations, as shown in 

 Figure 7.16, are generally on the order of 3 seconds or less. 



