Fences have two distinct advantages over planting. Sand fences may 

 be installed at any season, and are fully effective as soon as installed. 

 There is no waiting period for trapping capacity to develop. 



The volume of sand moved by strong winds may be too large to permit 

 the establishment of vegetation. Temporary protection with low fences 

 is a possible solution. 



The design of fence systems to stabilize areas of blowing sand should 

 consider the characteristics of the particular site, including wind pat- 

 tern and the ultimate configuration desired. Is the dune or dune field 

 migrating because there is net movement in the same direction every year? 

 If so, the first requirement is to stop movement from the upwind or sand 

 source side. Stabilization may then proceed as necessary. 



Field and laboratory studies have been made of the factors affecting 

 the performance of sand fences (Bagnold, 1942; Savage, 1963; Savage and 

 Woodhouse, 1968; Manohar and Bruun, 1970). The following summarizes 

 this work and provides some guidance in the use of sand fence for this 

 type of application. 



a. A fence porosity of 40 to 50 percent is the most efficient in 

 stopping sand movement and encouraging the deposition of sand. The 

 standard wooden fence made of slats, 3.8 centimeters wide by 1 centimeter 

 thick, is the most practical and cost-effective, and is readily available 

 in the United States. 



b. Double rows of fences are more effective than single rows when 

 windspeeds are high. Manohar and Bruun (1970) stated that a single fence 

 ceases to trap sand at windspeeds above 58 kilometers per hour while a 

 double fence continues to be effective above that speed. 



c. The most efficient spacing for multiple fences is about four 

 times the fence height (4h) apart or about 5 meters for a standard 

 1.2-meter slat fence. 



d. Trapping efficiency increases as the number of fence rows increase 

 while scour and secondary deposition decrease. The practical number of 

 rows in a set is limited to about four. 



A multiple installation three or four rows deep spaced 4h apart and 

 placed near the base of the windward slope of a bare dune will effectively 

 catch sand from that edge until the fences are filled. However, on large 

 areas of blowing sand, this design will need to be repeated downwind at 

 short intervals to keep scouring between installations under control. 

 The exact spacing for any given site is best determined through observa- 

 tion after the initial installation. 



Since the direction of winds is not constant on most sites, a grid 

 system of fences arranged in squares or rectangles may be preferred to a 



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