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s s 



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1 1 



S 2 



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LEGEND 



RETURN PERIOD, YRS 



. H.9 FT 

 13. B FT 

 12.6 FT 



STAGE FREQUENCY 



ROUGHANS POINT INTERIOR 



NORTH UALL COMPARISONS 



UIDE BERM + 1 FT CAP 



Figure 40. Effect of northern structure height on the "Wide Berm 

 + 1-ft Cap" alternative 



discussed in Part V, Roughans Point has a limited volume capacity. When the 

 amount of overtopping surpasses the capacity of the interior, the water pours 

 out over roadways into another drainage area. Therefore, although the various 

 alternatives are still producing very different overtopping rates, the flood 

 levels that result are similar for the highest return periods. 



94. Although the "Two Berms" alternative produced results very sim- 

 ilar to the "Wide Berm + 1-ft Cap" alternative, the "Two Berms" structure is 

 not a recommended alternative. The physical model tests showed the "Two 

 Berms" structure was not stable. For details see Ahrens and Heimbaugh (in 

 preparation) . 



95. The wide berm configuration proved to be effective in lowering 

 overtopping at the still-water levels which accompany return periods less than 

 100 years. Notice, however, that in Figure 36 the "Wide Berm" curve crosses 

 above the "Original Proposal" curve at about 150 years. The berm loses its 

 effectiveness in reducing overtopping as the higher still-water levels sub- 

 merge it. 



96. The effectiveness of the berm is dramatically improved by adding 



71 



