2. Water Levels and Currents — Storm Surge and Astronomical Tides . 



The following calculations establish design water levels at the island 

 site using the methods of Chapter 3 and supplemented by data for the Delaware 

 Bay area given in Bretschneider (1959) and U.S. National Weather Service 

 (formerly U.S. Weather Bureau) (1957) . 



a. Design Hurricanes . For illustrative purposes use hurricanes "A" and 

 "B" given by Bretschneider (1959). 



Hurricane A 



Radius to maximum winds = R = 62.04 km (33.5 nmi) 



Central pressure AP = 55.88 mm Hg (2.2 in. Hg) 



Forward speed V^ = 27.78 to 46.30 km/hr 



(15 to 25 knots) 

 (use V^ = 46.30 km/hr) 



Maximum gradient windspeed (eq. 3-63a) 



U„^^ = ^•^'*1 U4.5 [p - p 1^^^ - R(0.31)f] 

 max ^'^n o-' 



where for latitude 40 degrees N 



f = 0.337 



U^^ = 0-^^7 [14.5 (55.88)^^^ - 62.04(0.31)(0.337) ] 



U = 45.55 m/s (163.98 km/hr) 



max 



Maximum sustained windspeed (eq. 3-62) for Vx, = 46.3 km/hr 



U„ = 0.865 U + 0.5 V„ 



R max F 



U = 0.865 (163.98) + 0.5 (46.3) 



n 



U„ = 165 km/hr 



n 



Hurricane B 



R = 62.04 km (33.5 nmi) 



V^^ = 46.30 km/hr (25 knots) 



l^j^ = 8.05 km/hr greater than Hurricane A (8.05 km/hr = 2.23 m/s) 

 Calculate AP for U^^^^ = (163.98 + 8.05) km/hr 



l^ = 172.03 km/hr (47.79 m/s) 



8-7 



