of the finer sizes of sand. Daytona Beach, Florida, is a good example 

 of a gently sloping beach composed of fine sand. 



lo43 BREAKERS 



As a wave moves toward shore, it reaches a depth of water so shallow 

 that the wave collapses or breaks. This depth is equal to about 1.3 times 

 the wave height. Thus a wave 3 feet high will break in a depth of about 

 4 feet. Breaking can occur in several different ways (plunging, spilling, 

 surging, or collapsing). Breaking results in a dissipation of the energy 

 of the wave and is manifested by turbulence in the water. This turbulence 

 stirs up the bottom materials. For most waves, the water travels forward 

 after breaking as a foaming, turbulent mass, expending most of its remain- 

 ing energy in a rush up the beach slope. 



1.44 EFFECTS OF WIND WAVES 



Wind waves affect beaches in two major ways. Short steep waves, 

 which usually occur during a storm near the coast, tend to tear the 

 beach down. (See Figure 1-7.) Long swells, which originate from dis- 

 tant storms, tend to rebuild the beaches. On most beaches, there is a 

 constant change caused by the tearing away of the beach by local storms 

 followed by gradual rebuilding by swells. A series of violent local 

 storms in a short time can result in severe erosion of the shore if 

 there is not enough time between storms for swells to rebuild the 

 beaches. Alternate erosion and accretion of beaches may be seasonal 

 on some beaches; the winter storms tear the beach away, and the summer 

 swells rebuild it. Beaches may also follow long-term cyclic patterns. 

 They may erode for several years, and then accrete for several years. 



1.45 LITTORAL TRANSPORT 



Littovat transport is defined as the movement of sediments in the 

 nearshore zone by waves and currents and is divided into two general 

 classes; transport parallel to the shore (longshore transport) and 

 transport perpendicular to the shore (on shore- offshore transport). This 

 transport is distinguished from the material moved, which is called 

 littoral drift. 



Onshore -offshore transport is determined primarily by wave steepness, 

 sediment size, and beach slope. In general, high steep waves move material 

 offshore, and low waves of long period (low steepness waves) move material 

 onshore. This onshore-offshore process associated with storm waves is 

 illustrated in Figure 1-7. 



Longshore transport results from the stirring up of sediment by the 

 breaking wave, and the movement of this sediment by the component of the 

 wave in an alongshore direction, and by the longshore current generated 

 by the breaking wave. The direction of longshore transport is directly 

 related to the direction of wave approach, and the angle of the wave to 

 the shore. Thus, due to the variability of wave approach, longshore 



l-IO 



