basins permits large tropical or extratropical storms to be situated entirely 

 over water areas allowing tremendous energy to be transferred from the 

 atmosphere to the water. Wind-induced surface currents, when moving from the 

 deep ocean to the coast, are impeded by the shoaling bottom; this impediment 

 causes an increase in water level over the Continental Shelf. 



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 

 stonn'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, 

 neglecting the contribution of astonomical tide, 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 variations of maximum surge values and their 

 times for many locations along the east coast during Hurricane Carol (1954) 

 are shown in Figure 3-57. 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, 

 windfield, 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 theoretically storm surge on the open coast and in 

 bays and estuaries require verification. 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 satisfactory verification. Estimates of the water 

 level on the open coast from levels observed at inland locations are un- 

 reliable, since corrective adjustments must be made to the data, and the 

 transformation is difficult. An evaluation of certain storm surge models and 

 examples of comparisons between model results and observations are provided by 

 the Committee on Tidal Hydraulics (1980). 



Systematic acquisition of hurricane data by a number of organizations and 

 individuals began during the first quarter of this century. Harris (1963) 

 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. 



3-123 



