setup or storm surges are created by strong winds. The height of stomi 

 surge depends on wind velocity and dii'ection, fetch, water depth, ajid 

 ncarshore slope. In violent storms, storm surge may raise sea level at 

 the shore as much as 20 feet. In the United States, larger surges occur 

 on the Gulf coast because of the shallower and broader shelf off that 

 coast compared to the shelves off the Atlantic and Pacific coasts. Storm 

 surges may also be increased by a funneling effect in converging estuaries. 



When waves approach the beach at an angle, they create a current in 

 shallow water parallel to the shore, known as the lotuji^hovc c-'uvveyit. This 

 current, under certain conditions, may turn and run out to sea in what is 

 known as a rip aurvent. 



1.34 TIDAL CURRENTS 



If water level rises :uid falls at an area, then water must flow into 

 and out of the area. Significant currents generated by tides occur at in- 

 lets to lagoons and bays or at entrances to harbors. At such constricted 

 places, tidal currents generally flow in when the tide is rising (flood 

 tide) and flow out as the tide falls (ebb tide). Exceptions can occur 

 at times of high river discharge or strong winds, or when density cur- 

 rents are an important part of the current system. 



In addition to creating currents, tides const juitly chaiige the level 

 at which waves attack the bcnclu 



1.4 THE BEHAVIOR OF BEACHES 



1.41 BEACH COMPOSITION 



The size and character of sediments on a beacli ai"e related to forces 

 to which the beach is exposed and the type of material available at the 

 shore. Most beaches are composed of fine or coarse sand and. in some 

 areas, of small stones called shingle or gravel. This material is sup- 

 plied to the beach zone by streams, by erosion of the shores caused by 

 waves and currents and, in some cases, by onshore movement of material 

 from deeper water. Clay and silt do not usually remain on ocean beaches 

 because the waves create such turbulence in the water along the shore 

 that these fine materials ;ire kept in suspension. It is only after nnw- 

 ing away from the beaches into quieter or deeper water that these fine 

 particles settle out and deposit on the bottom. 



1.42 BEACH CHARACTERISTICS 



Characteristics of a beach are usually described in terms of average 

 size of the sand particles that make up the beach, range and distribution 

 of sizes of those particles, sand composition, elevation and width of berm, 

 slope or steepness of the foreshore, the existence (or lack) of a bar, and 

 the general slope of the inshore zone fronting the beach. Generally, the 

 larger the sand particles tlic steeper the beach slope. Beaches witli 

 gently sloping foreshores and inshore zones usually have a prepondor.ince 



1-9 



