four times the fence height. A 4-foot fence requires fence lines to be 

 16 feet apart, see third and fourth lifts in Figure 6-32. This arrange- 

 ment is most efficient in trapping sand, and forms a more uniform dune. 

 Positioning the second lift on the slope of the existing dune will increase 

 both its height and width. The actual sequence of installation of the 

 fence may alternate between a position on the crest, along the slope, or 

 offset to the existing dune. 



(h) The trapping capacity of the initial installation and succeed- 

 ing lifts of a 4-foot high sand fence averages between 2 and 3 cubic yards 

 per linear foot. (See Figures 6-31 and 6-32.) 



(i) CERC's experience has been that on the average 6 man-hours 

 were required to erect 235 feet of wooden, picket-type fence or 185 feet 

 of fabric fence when a six-man crew had materials available at the site 

 and used a mechanical posthole digger. 



(j) Unless maintained, dunes created by fencing are short-lived, 

 because of corrosion of wire, deterioration of wood (Figure 6-33), and 

 vandalism. 



(k) Junk cars should not be used for dune building. They are more 

 expensive and less effective than fencing. (Gage, 1970.) Junk cars mar 

 the beauty of a beach, and create a safety hazard. 



. - -*-^-3\; ^^?s-^: 



if-. ' 



Figure 6-33. Sand Fence Deterioration Due to Exposure and Storms 



6-42 



