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. 



d. 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 important 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. 



e. Carbonate Production . Dissolved calcium carbonate concentration in 

 the ocean is near saturation, and it may be precipitated under favorable 

 conditions. In tropical areas, many beaches consist of calcium carbonate 

 sands; in temperate zones, calcium carbonate may be a significant part of the 

 littoral material. These calcium carbonate materials are generally fragments 

 of shell material whose rate of production appears to increase with high 

 temperature and with excessive evaporation (see Hayes, 1967b). Oolitic sands 

 are a nonbiogenic chemical precipitate of calcium carbonate on many low- 

 latitude beaches. 



Quantitative estimates of the production of calcium carbonate sediment 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 contribution to the 

 littoral zone from such a source would assume an average shell thickness of 

 about 0.012 meter (0.04 foot) completely covering a strip of beach 30 meters 

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

 0.07 cubic meter per year per meter (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 production can be much higher. 



f. 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 Engineer District offices, 

 in records of local government, and in dredging company records. The exact 

 computation of the quantity of a beach fill is subject to uncertainties: the 

 source of the dredged sand often contains significant but variable quantities 

 of finer materials that are soon lost to the littoral zone; the surveys of 

 both the borrow area and the replenished area are subject to uncertainty 

 because sediment transport occurs during the dredging activities; and in 

 practice only limited efforts are made to obtain estimates of the size dis- 

 tribution of fill placed on the beach. Thus, the resulting estimate of the 

 quantity of suitable fill placed on the beach is uncertain, but the most 

 reliable of the items in the budget. More frequent sampling and surveys could 

 help identify this significant element in many sediment budgets. 



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