B-26. OVERTOPPING 



Studies of the estimated volume of water that would over- 

 top the barriers were estimated using data obtained from a report 

 entitled "Summary Report (Project CW-167)> Waves and Wind Tides 

 in Shallow Lakes and Reservoirs," published by the U.S. Amiy 

 Ehgineer District, Jacksonville. 



The amoimt of overtopping at the Fox Point barrier (without 

 Lower Bay barriers) for the design tidal flood condition is estimated 

 to be at an average rate of 1 cubic foot per second per foot, or, 

 for the 800-foot effective length, 800 cubic feet per second. This 

 is equivalent to 65 acre-feet or a 1.5 foot rise per hour over the 

 iiO acres of water area; however, the pumps would be designed to 

 keep the rise negligible. Overtopping would be eliminated with 

 the Lower Bay barriers. 



The amount of overtopping at the Lower Bay barriers for the 

 design condition is tabulated below: 



Effective Length Rate 



of of 



Barrier Barrier Overtopping 



(ft.) (c.f.s. per ft.) (total c.f.s.) 



East barrier 2,000 10 20,000 



West barrier 5,000 6 30,000 



Tiverton barrier 5,000 2 10,000 



Total 60,000 



The approximate overtopping of 60,000 c.f.s. is equivalent 

 to 5>000 acre-feet per hour, or a rise of about 0.1 foot per hour 

 in the 120-square-mile water area above the Lower Bay barriers. 

 Therefore, the rise in level would be about O.U foot in a U-hour 

 period of overtopping. Further studies are required on over- 

 topping for riprap slopes and vertical walls. 



B-27. suwi/uiy 



Based on the foregoing model tests and analytical calculations, 

 the reductions in tidal flooding with the Lower Bay barriers are 

 shown in Table B-7. 



B-26 



