PART VI: STAGE FREQUENCY RELATIONSHIPS 
Introduction 
182. The products of this portion of the study are stage-frequency 
curves which relate the elevation of flood waters to the average waiting time 
between floods of equal or greater severity. The ordinate of these curves is 
stage, measured in feet NGVD, and the abscissa is return period expressed in 
years. 
183. Flooding in the study area is caused by the combination of storm- 
induced water level and astronomical tide. Storm-induced water level has two 
main components, storm surge and wave-induced water level. Storm surge is 
composed of the combined effects of storm winds piling water along the shore 
and low barometric pressure raising the water surface. The wave component is 
produced by breaking waves; a portion of the momentum of the waves is trans- 
formed into a rise in water level called wave setup. This project is pri- 
marily concerned with the combined effects of storm surge and tide. However, 
an estimate is made of the contribution due to wave setup in areas where this 
effect is considered important. 
184. Two distinct classes of storms affecting the study area are north- 
easters and hurricanes. Northeasters, named after the predominant direction 
of the associated winds, are large-scale, low pressure disturbances which usu- 
ally occur from late September through April. Wind speeds associated with a 
northeaster are generally less than those of a hurricane. Although gusts can 
reach hurricane strength in a very severe northeaster, sustained wind speeds 
are rarely greater than 50 knots. Flood damage caused by a northeaster is a 
function of the storm's duration and intensity. Storms of longer duration are 
more likely to destroy both natural and engineered flood protection features. 
Also, since a northeaster may last several days, the possibility of a storm 
occurring simultaneously with a spring tide increases, thereby increasing 
potential flood damage. An average of 2.4 northeasters per year with maximum 
storm surges greater than 2.5 ft affect the study area (Prater, Hardy, and 
Butler in preparation). The maximum recorded northeaster storm surge near the 
study area was 8.5 ft, which occurred during the November 1950 storm. 
185. Hurricanes are a rarer occurrence in the study area. By the time 
hurricanes approach the latitudes of the northern New Jersey coast, they are 
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