needed 20 to 50 years from now. They can 

 provide a "base-line" for detecting and document- 

 ing changes in the environment caused by large- 

 scale introduction of materials and energy. 



Such conservation of selected sites is of great 

 scientific interest It cannot be foreseen what basic 

 questions man may wish to ask a century from 

 now, or what measurements with yet-to-be- 

 developed methods he may have to make to 

 answer these questions. Eventually we will want to 

 rehabilitate our polluted environments. To do so 

 will be very difficult if an undisturbed ecosystem 

 of a comparable kind cannot be studied as a 

 standard. Probably, there is today no estuary left 

 on the U.S. east and Gulf coasts which is not 

 measurably altered by man. In the future these 

 changes are likely to accelerate because the rate of 

 discharge of pollutant per capita increases with 

 progressing industrialization of a country, apart 

 from the continuing population growth. If there 

 are no relatively unaffected areas set aside now, 

 the only scientific standard or base-line in a 100 

 years will be the then-least-altered environment, 

 which may be heavily polluted by today's stand- 

 ards. 



An unspoiled area in the Pacific Northwest cannot 

 serve as a fully representative site for east coast 

 purposes because of the different plants and 

 animals living in the two regions. Therefore, we 

 should set aside preserves in the cool and warm 

 regions of both the U.S. east and west coasts, and 

 on the Gulf coast. Furthermore, in addition to 

 preserves in estuaries, we should protect subtidal 

 areas on open coasts. 



VII. COASTAL ENGINEERING RESEARCH 



Characteristics of a beach are determined by 

 the forces to which the beach is exposed and the 

 type of material available at the shore. Most 

 beaches are composed of sand. The sand is 

 supplied by the streams flowing into the ocean and 

 by the erosion of the shores by waves and 

 currents. Stone and mud beaches are relatively 

 rare. Grasses usually grow in the mud; thus these 

 shores are marshes. Mud and marsh beaches are 

 found only where wave action is very mild.' 



'a detailed discussion of coastlines can be found in 

 William C. Putnam et al. Natural Coastal Environments of 

 the World, ONR Contract Nonr-233(06), NR 388-013 

 (Universityof California, 1960). 



The characteristics usually used to describe a 

 beach are: the average size of sand particles 

 making up the beach, the range of sizes of those 

 particles, the slope or steepness of the foreshore, 

 and the general slope of the underwater portion of 

 the beach from the foreshore toward deeper water 

 (see Figure 5). Generally, the larger its sand 

 particles, the steeper the beach.* 



The short, steep waves of winter storms erode 

 the beaches, taking the material from above sea 

 level and carrying it into deeper water. Most of it 

 is returned by the low, long swells of a typical 

 summer season. Waves breaking at an angle to the 

 beach set up currents which move parallel to the 

 shore in shallow water. These long shore currents 

 carry the beach sand— which has been stirred into 

 suspension by the turbulence of the breaking 

 waves— along the shore parallel to the beach. 



Fresh water from rivers and upland streams 

 flows to the sea, in some cases directly into the 

 ocean and in other cases through bays or sounds. 

 In this way sediments brought down by rivers and 

 streams feed the ocean beaches. Beaches thus 

 continually change. Sediment brought by rivers is 

 winnowed and sorted by the along-shore move- 

 ment of the beach sand the onshore-offshore sand 

 movement caused by low swells and steep waves. 



A particularly severe winter storm or hurricane 

 may erode a beach to the extent that it will take 

 several years to recover. Breakwaters may cause 

 permanent changes in local beach conditions. On a 

 National average our beaches are eroding. They are 

 eroding largely because rivers no longer carry a 

 replenishing sediment load to the oceans as in the 

 past. Water diversion, which reduces river flow, 

 and dams, which trap sediment— both reduce the 

 availabiUty of beach sand. An examination of 

 records shows that eroding beaches are the general 

 rule around our coasts and that accreting beaches 

 are rare. 



The relations between wind, waves, tides, sea 

 level, and beach stability (or instability) are very 

 comphcated. The relations are fairly well under- 

 stood on a qualitative basis but are insufficiently 

 identified on a quantitative basis. The design of 



This description and much of the following material 

 is taken from Land Against the Sea, U.S. Army Coastal 

 Engineering Research Center Misc. Paper 4-64, May 1964, 

 and Joseph M. Caldwell, "Coastal Processes and Beach 

 Erosion," Journal of the Society of Civil Engineers, Vol. 

 53, No. 2, April 1966. 



111-78 



