peat, in the littoral zone depends on the wave climate, contributions of fine 

 sediment from rivers and other sources, and recent geologic history. Fine 

 grain-size material is common in the littoral zone wherever the annual mean 

 breaker height is below about 0.3 meters. Fine material is found at or near 

 the surface along the coasts of Georgia and western Florida between Tampa and 

 Cape San Bias and in large bays such as Chesapeake Bay and Long Island Sound. 



Table 4-3. Minerals occurring in beach sand. 



These are light minerals with specific gravities not exceeding 2.87. The 

 remaining minerals are heavy minerals with specific gravities greater 

 than 2.87. Heavy minerals make up less than 1 percent of most beach 

 sands. 



These are all areas of low mean breaker height. In contrast, fine sediment is 

 seldom found along the Pacific coast of California, Oregon, and Washington, 

 where annual mean breaker height usually exceeds 0.8 meters. 



Where rivers bring large quantities of sediment to the sea, the amount of 

 fine material remaining along the coast depends on the balance betveen wave 

 action acting to erode the fines and river deposition acting to replenish the 

 fines (Wright and Coleman, 1972) . The effect of the Mississippi River delta 

 deposits on the coast of Louisiana is a primary example. 



Along eroding, low-lying coasts, the sea moves inland over areas formerly 

 protected by beaches, so that the present shoreline often lies where tidal 

 flats, lagoons, and marshes used to be. The littoral materials on such coasts 

 may include silt, clay, and organic material at shallow depths. As the active 

 sand beach is pushed back, these former tidal flats and marshes then outcrop 

 along the shore (e.g., Kraft, 1971). Many barrier islands along the Atlantic 

 and gulf coasts contain tidal and marsh deposits at or near the surface of the 

 littoral zone. The fine material is often bound together by the roots of 



4-22 



