Table 4-5. Factors influencing erosion caused by storms. 



For example, erosion tends to increase when wave height is high, wave period is low, beach slope 

 is high, etc. 



Depending on the path of the storm and the angle of the waves, a signif- 

 icant amount of material can also be moved alongshore. If the direction of 

 longshore transport caused by the storm is opposite to the net direction of 

 transport, the sand will probably be returned in the months after the storm 

 and permanent beach changes effected by the storm will be small. If the 

 direction of transport before, during, and after the storm is the same, then 

 large amounts of material could be moved by the storm with little possibility 

 of restoration. Successive storms on the same beach may cause significant 

 transport in opposite directions (e.g.. Everts, 1973). 



There are some unique events that are only accomplished by catastrophic 

 storms. The combination of storm surge and high waves allows water to reach 

 some areas not ordinarily attacked by waves. These extreme conditions may 

 result in the overtopping of dunes and in the formation of washover fans and 

 inlets (Morgan, Nichols, and Wright, 1958; Nichols and Marston, 1939; Howard, 

 1939; Leatherman et al., 1977). Some inlets are periodically reopened by 

 storms and then sealed by littoral drift transported by normal wave action. 



For a given storm, greater effects can be expected at beaches with lower 

 average wave climates. In a high-energy climate, storm waves are not much 

 larger than ordinary waves and their effects may not be significant; an 

 example of this might be northeasters occurring at Cape Cod. In a low-energy 

 climate, where transport volumes are usually low, storm waves can move 

 significant amounts of sand, as do hurricanes on the gulf coast. 



The effects of particular storms on certain beaches are described in the 

 following paragraphs. These examples illustrate how an extreme event may 

 affect the beach. 



4-44 



