PART IV: WAVE MODELING 



34. For each event (surge plus tide), the wave climate in a 25.9- 

 square mile area of Broad Sound was simulated for each hour when the still- 

 water level was above 7.0 ft NGVD. The area considered is shown in Fig- 

 ure 24. Depths, at mean low water, range from ft at the beaches to 

 approximately 82 ft along the eastern boundary of the grid. The shallow 

 depths in the area required the use of a shallow-water wave model. 



35. A steady-state, shallow-water, directional-spectral wave model 

 (ESCUBED) was used to perform the simulations. The required simulations 

 actually called for the use of a time-dependent model, but the cost of using 

 such a model was prohibitive. In lieu of a truly transient simulation, 

 ESCUBED was run once for each hour of each event, and the resulting wave 

 climate was taken to be representative of the conditions existing for the 

 entire hour. 



36. For each run of ESCUBED it was necessary to specify a directional 

 spectrum at points along the eastern boundary of the grid shown in Figure 24. 

 To do this, wave train characteristics (e.g. significant wave heights and 

 peak spectral wave periods) were used to define the TMA spectral shape (Hughes 

 1984), and the resulting one-dimensional spectrum was then distributed direct- 

 ionally. The wave train characteristics represented both sea and swell and 

 were derived using the methods and data of WIS. 



37. A total of 848 hr of simulation was made. Resulting wave heights 

 in the lee of Nahant peninsula indicated that local wave generation in this 

 area was inadequately simulated by ESCUBED. Hence, an additional analysis was 

 required when winds were from the northeast. 



38. Shallow-water wave growth equations were used to estimate locally 

 generated wave heights and periods off the north seawall at Roughans Point as 

 well as at Point of Pines and in Lynn Harbor. The total wave climate in these 

 regions was then assumed to be a combination of these locally generated waves 

 and the ESCUBED results. 



39. It is important to note that no wave data from Broad Sound were 

 available. Hence, it was not possible to calibrate ESCUBED or to verify its 

 results. 



40. The following sections discuss the WIS methods and data, the 

 ESCUBED wave model, and the analysis of local wave generation in the lee of 

 Nahant Peninsula. 



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