SCHEDULE FENCE ERECTION 



Time ( Monttis ) Lift Number 



I 



12 2 



24 3,4 



14 - 

 12 ■ 

 10- 



8 



6 



4 



20 



60 



_i_ 



100 



(fll 



_l_ 



120 



140 



160 



180 



_!_ 



200 



20 30 



(m) 

 Distonce from Base Line 



40 



50 



60 



Figure 6-31. Sand fence dune with lifts positioned parallel to the existing 

 fence, Padre Island, Texas. 



(m) Fence-built dunes must be stabilized with vegetation or the fence 

 will deteriorate and release the sand (Fig. 6-32). While sand fences ini- 

 tially trap sand at a high rate, established vegetation will trap sand at 

 a rate comparable to multiple lifts of sand fence (Knutson, 1980). The 

 construction of dunes with fence alone is only the first step in a two- 

 step operation. 



Fences have two initial advantages over planting that often warrant their 

 use before or with planting: (a) Sand fences can be installed during any 

 season and (b) the fence is immediately effective as a sand trap once it is 

 installed. There is no waiting for trapping capacity to develop in comparison 

 with the vegetative method. Consequently, a sand fence is useful to accu- 

 mulate sand before planted vegetation is becoming established. 



4. Dune Construction Using Vegetation . 



a. Plant Selection . Few plant species survive in the harsh beach 

 environment. The plants that thrive along beaches are adapted to conditions 

 that include abrasive and accumulating sand, exposure to full sunlight, high 

 surface temperatures, occasional inundation by saltwater, and drought. The 

 plants that do survive are long-lived, rhizomatous or stoloniferous perennials 

 with extensive root systems, stems capable of rapid upward growth through 

 accumulating sand, and tolerance of salt spray. Although a few plant species 



6-43 



