Onshore winds, cause the water level to begin to rise at the edge of the 

 Continental Shelf. The amount of rise increases shoreward to a maximum 

 level at the shoreline. Storm surge at the shoreline can occur over long 

 distances along the coast. The breadth and width of the surge will depend 

 on the storm's size, intensity, track and speed of forward motion as well ' 

 as the shape of the coastline, and the offshore bathymetry. The highest 

 water level reached at a location along the coast during the passage of a 

 storm is called the maximum surge for that location; the highest maximum 

 surge is called the peak surge. Maximum water levels along a coast do not 

 necessarily occur at the same time. The time of the maximum surge at one 

 location may differ by several hours from the maximum surge at another 

 location. The variation of maximum surge values and their time for many 

 locations along the east coast during Hurricane Carol, 1954, are shown in 

 Figure 3-44. This hurricane moved a long distance along the coast before 

 making landfall, and altered the water levels along the entire east coast. 

 The location of the peak surge relative to the location of the landfall 

 where the eye crosses the shoreline depends on the seabed bathymetry, wind- 

 field, configuration of the coastline, and the path the storm takes over 

 the shelf. For hurricanes moving more or less perpendicular to a coast 

 with relatively straight bottom contours, the peak surge will occur close 

 to the point where the region of maximum winds intersects the shoreline, 

 approximately at a distance R, to the right of the storm center. Peak 

 surge is generally used by coastal engineers to establish design water 

 levels at a site. 



Attempts to evaluate storm surge on the open coast, and also in bays 

 and estuaries, when obtained entirely from theoretical considerations, 

 require verification particularly when simplified models are used. The 

 surge is verified by comparing the theoretical system response and computed 

 water levels with those observed during an actual storm. The comparison is 

 not always simple, because of the lack of field data. Most water-level 

 data obtained from past hurricanes were taken from high water marks in low- 

 lying areas some distance inland from the open coast. The few water-level 

 recording stations along the open coast are too widely separated for satis- 

 factory verification. Estimates of the water level on the open coast from 

 levels observed at inland locations are unreliable, since corrective adjust- 

 ments must be made to the data, and the transformation is difficult. 



Systematic acquisition of hurricane data by a number of organizations 

 and individuals began during the first quarter of this century. Harris 

 (1963b) presented water-level data and synoptic weather charts for 28 

 hurricanes occurring from 1926 to 1961. Such data are useful for verifying 

 surge prediction techniques. 



Because of the limited availability of observed hurricane surge data 

 for the open coast, design analysis for coastal structures is not always 

 based on observed water levels. Consequently a statistical approach has 

 evolved that takes into account the expected probability of the occurrence 

 of a hurricane with a specific CPI at any particular coastal location. 

 Statistical evaluation of hurricane parameters based on detailed analysis 

 of many hurricanes, have been compiled for coastal zones along the Atlantic 

 and Gulf coasts of the U.S. The parameters evaluated were the radius of 



3-97 



