calibration and verification in this study produced excellent results. The 

 one-grid system used in this project should prove to be much more accurate 

 than a two-grid system because of the lack of wind data needed to force an 

 outer grid. The major source of potential error in the water level modeling 

 is the lack of storm data for calibration of the model. Implicit in cali- 

 brating the model to tide alone is the assumption that the magnitude of the 

 storm surge at the Boston tide gage is very close to the magnitude of the 

 storm surge in the study area for any storm event. Because the two locations 

 are so close to one another in comparison to the size of either the continen- 

 tal shelf or the size of a typical northeaster, this assumption is probably 

 more accurate than the alternative of using a two-grid system. Taking all 

 these factors into account, it is estimated that the accuracy of any one simu- 

 lation of the storm surge model would be within a few tenths of a foot in 

 areas close to the tide gages and within about one-half foot in those areas 

 west of the highway embankment. 



105. The wave modeling portion of the project was less accurate than 

 the water level modeling for four main reasons. First, the state of the art 

 in wave modeling, particularly in shallow water, is not as advanced as in 

 surge modeling. Second, the numerical wave model used is more recent than 

 WIFM and, therefore, less well tested. Third, there were no wave data 

 available for either calibration or verification of the model. And, fourth, 

 the boundary conditions for the wave modeling (the WIS hindcasts which are the 

 best available) were not as accurate as the gage data used for the water level 

 modeling. These four factors are somewhat offset by the fact, that, for all 

 the more severe wave conditions and for many of the times when overtopping 

 occurred at Roughans Point, the waves approaching the wall were depth limited. 



106. The flood routing model contained a series of assumptions for cal- 

 culating outflow from the interior of Roughans Point. For the flood levels 

 bracketed by the 1972 and 1978 floods, the flood routing model should produce 

 good results. However, for extreme floods, the interior water level is heav- 

 ily dependent upon the volume of water leaving the interior by flowing over 

 roadways and, for existing conditions, over reach D. Therefore, flood levels 

 higher than those produced by the 1978 event are more uncertain than are lower 

 flood levels. 



107. The probability model contained several processes which could 

 potentially introduce error into the final curves. These included assigning 



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