erosion of the nearshore bottom and beaches, but in the control volume 

 defined, this transport takes place within the control volume. Transport 

 from the offshore has been treated as a line source. 



In some places, offshore islands or shoals may act as point sources 

 of material for the littoral zone. For example, the drumlin islands and 

 shoals in Boston Harbor and vicinity may be point sources for the nearby 

 mainland. 



4.724 Windblown Sediment Sources . To make a net contribution to the 

 littoral zone in the time frame being considered, windblown sand must 

 come from a land source whose sand is not derived by intermediate steps 

 from the same littoral zone. On U.S. ocean coasts, such windblown sand 

 is not a significant source of littoral materials. Where wind is impor- 

 tant in the sediment budget of the ocean shore, wind acts to take away 

 sand rather than to add it, although local exceptions probably occur. 



However, windblown sand can be an important source, if the control 

 volume being considered is a beach on the lagoon side of a barrier island. 

 Such shores may receive large amounts of windblown sand. 



4.725 Carbonate Production . Dissolved calcium carbonate concentration 

 in the ocean is near saturation, and it may be precipitated under favor- 

 able conditions. In tropical areas, many beaches consist of calciiom car- 

 bonate sands; in temperate zones, calcium carbonate may be a significant 

 part of the littoral material. These calciiom carbonate materials are gen- 

 erally fragments of shell material whose rate of production appears to in- 

 crease with high temperature and with excessive evaporation. (See Hayes, 

 1967.) Oolitic sands are a nonbiogenic chemical precipitate of calcium 

 carbonate on many low latitude beaches. 



Quantitative estimates of the production of calcium carbonate sedi- 

 ment are lacking, but maximum rates might be calculated from the density 

 and rate of growth of the principal carbonate-producing organisms in an 

 area. For example, following northeasters along the Atlantic coast of 

 the U.S., the foreshore is occasionally covered with living clams thrown 

 up by the storm from the nearshore zone. One estimate of the annual con- 

 tribution to the littoral zone from such a source would assume an average 

 shell thickness of about 0.04 foot completely covering a strip of beach 

 100 feet wide all along the coast. On an annual basis, this would be 

 about 0.15-cubic yard per year per foot of beach front. Such a quantity 

 is negligible under almost all conditions. However, the dominance of 

 carbonate sands in tropical littoral zones suggests that the rate of pro- 

 duction can be much higher. 



4.726 Beach Replenishment . Beach protection projects often require 

 placing sand on beaches. The quantity of sand placed on the beach in 

 such beach-fill operations may be a major element in the local sediment 

 budget. Data on beach-fill quantities may be available in Corps of Engi- 

 neer District offices, in records of local government engineers, and in 

 dredging company records. The exact computation of the quantity of a 



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