maximum wind R; the minimiom central pressure of the hurricanes p ; 

 the forward speed of the hurricane V„, while approaching or crossing 



the coast; and the maximum sustained wind speed W, 30 feet above the 

 mean water level. 



Based on this analysis, the U.S. Weather Bureau (now the National 

 Weather Service) and U.S. Army Corps of Engineers jointly established 

 specific storm characteristics for use in the design of coastal struc- 

 tures. Because the parameters characterizing these storms are specified 

 from statistical considerations and not from observations, the storms 

 are termed hypothetical huvvioanes or hypo-hurriaanes . The parameters 

 for such storms are assumed constant during the entire surge generation 

 period. Graham and Nunn (1959) have developed criteria for a design storm 

 where the central pressure has an occurrence probability of once in 100 

 years. This storm is referred to as the standard project hurr-ioane (SPH) . 

 The mathematical model used for predicting the wind and pressure fields in 

 the SPH is discussed in Section 3.72, Model Wind and Pressure Fields for 

 Hurricanes. The SPH is defined as a "hypo-hurricane that is intended to 

 represent the most severe combination of hurricane parameters that is 

 reasonably oharaateristia of a region excluding extremely rare combina- 

 tions." Most coastal structures built by the U.S. Army Corps of Engineers 

 that are designed to withstand or protect against hurricanes are based on 

 design water associated with the SPH. 



The construction of nuclear-powered electric generating stations in 

 the coastal zone made necessary the definition of an extreme hurricane 

 called the probable maximum hurricane (PMH) . The PMH has been adopted by 

 the Atomic Energy Commission for design purposes to ensure public safety 

 and the safety of nuclear-power facilities. Procedures for developing a 

 PMH for a specific geographical location are given in U.S. Weather Bureau 

 Interim Report HUR 7-97 (1968). The PMH was defined as "A hypothetical 

 hurricane having that combination of characteristics which will make the 

 most severe storm that is reasonably possible in the region involved, if 

 the hurricane should approach the point under study along a critical path 

 and at an optimum rate of movement." 



Selection of hurricane parameters and the methods used for developing 

 overwater wind speeds and directions for various coastal zones of the 

 United States are discussed in detail by Graham and Nunn (1959) and in 

 HUR 7-97 (1968) for the SPH and PMH. The basic design storm data should 

 be carefully determined, since errors may significantly affect the final 

 results. 



Two simple methods are presented here for estimating storm surge on 

 the open coast: one a quasi-static numerical scheme and the other a nomo- 

 graph method. These methods should never be used for estimating the surge 

 in bays, estuaries, rivers or in low-lying regions landward of the normal 

 open-coast shoreline. Neither method is entirely satisfactory for all 

 cases, but for many problems both appear to give reasonable solutions. 

 The use of each method is illustrated by estimating the peak open- coast 

 storm surge for an actual hurricane. The peak surges thus calculated are 

 compared to the surge computed by a complete two-dimensional numerical 

 model for the same storm. 



3-100 



