(10) Accumulation of sand by fences is not constant and 

 varies widely with location, season of the year, and from year 

 to year. Fences may remain empty for months following instal- 

 lation, only to fill within a few days by a single storm. In 

 order to take full advantage of available sand, fences must be 

 observed regularly, repaired if necessary, and new fences in- 

 stalled as existing fences fill. Usually where appreciable 

 sand is moving, a single 1.2-meter fence will fill within 1 

 year. 



c. Results . Extensive dunes have been built using sand fences on 

 the Atlantic, gulf, and Pacific coasts of the United States as well as 

 along the coast of northern Europe. Sand accumulation rate depends on 

 the amount of moving sand and varies widely. It may range from in excess 

 of 10 cubic meters per meter of beach per year to less than 1 cubic meter 

 per meter of beach. 



d. Limitations . While sand fences are very effective in trapping 

 windblown sand, when the fences are filled they have little or no further 

 effect on sand movement. Fence-built dunes must be stabilized or the 

 fence will deteriorate and release the sand. 



Except for certain specialized applications, vegetation is the only 

 feasible long-term means of stabilizing sand dunes. Although some fence- 

 built dunes become vegetated naturally under unusually favorable circum- 

 stances, the planting of vegetation on fence-built dunes is usually 

 essential to their survival. The construction of dunes with fence 

 alone is only the first step in a two-step operation. 



e. Advantages . Fences have two initial advantages over planting 

 which often warrant their use before or with planting: (a) Sand fences 

 can be installed during any season, and (b) the fence is fully effective 

 as a sand trap as soon as it is installed. There is no waiting for 

 trapping capacity to develop in comparison with the vegetative method. 



Consequently, a sand fence can be useful in accumulating sand 

 before planting or while planted vegetation is becoming established. 

 For example, the trapping of blowing sand to form a foredune along the 

 mid-Atlantic coast could begin any month in the year using sand fence. 

 Trapping by planting could only be accomplished by planting in late 

 winter or spring and no substantial accumulation would develop for 

 several months later in the summer. 



Moreover, on extensive dunes and dune fields, the volume of sand 

 moved by strong winds may be too large to permit the unassisted estab- 

 lishment of vegetation. Plants may be blown out before establishment. 



3. Vegetation . 



a. Role . Sand dunes are built and stabilized naturally by vegeta- 

 tion. Vegetation is usually less e'xpensive, more durable, more pleasing 



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