51 



5. STORM SURGE AND WIND-WAVE RESPONSE 



5 . 1 INTRODUCTION 



Storm surge is the response of mean water level to the high winds, 

 pressure differential, and rainfall associated with tropical (hurricane) 

 and extratropical (northeaster) storms. The forces which appear to elicit 

 the greatest responses are wind- induced shear, which tends to push water 

 onto the beach, and the inverse barometer effect, which elevates the water 

 level under the eye of a hurricane. For example. Fig. 5.1 displays the 

 observed tides and storm surge associated with Hurricane Carla in the 

 Galveston, Texas area. A complete discussion of all the relevant forces 

 and the equations governing flows induced by storms can be found in the 

 Shore Protection Manual, U.S. Army Corps of Engineers (1984). Solutions to 

 idealized cases are given by Bretschneider (1966a) and Dean and Dalrymple 

 (1984) . The dependence of these solutions on nominal water depth will be 

 examined in order to postulate some of the possible effects of long-term 

 sea level rise. 



The stress applied to the water by the high winds associated with 

 storms is also responsible for wave generation. Bretschneider (1959) 

 developed a family of curves from non-dimensional significant wave height 

 induced by a hurricane, shown in Fig. 5.2. Wind waves are affected by sea 

 level (water depth) both in their generation and as they propagate over the 

 continental shelf. Shallow water limits the height a growing wave can 

 attain due to steepness -induced breaking and bottom friction, while bottom 

 friction continues to drain energy from the waves as they propagate out of 

 the generation region. Wave generation in shallow water and losses due to 

 bottom friction will be briefly examined in order to identify effects of 

 depth, and hence the consequences of long-term sea level rise. Reference 

 can be made again to the Shore Protection Manual and Bretschneider (1966b) 

 for information on these topics. 



5.2 STORM SURGE 



For the idealized situation shown in Fig. 5.3a where the continental 

 shelf is uniform in depth, we consider a spatially and temporally uniform 



