Appendix 6.3(37). Dune stabilization practices. 



Vegetation stabilizes dunes both internally by means of an extensive 

 root system and externally by covering the surface material and trapping 

 new material. Few plant species are able to survive in the harsh beach 

 environment. To be successful, the species must be adaptable to abrasive 

 and accumulating sand, exposure to full sunlight, high surface temperature, 

 occasional inundation by salt water, salt spray, 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 ac- 

 cumulating sand, and tolerance of salt spray (Coastal Engineering Research 

 Center 1973). In the Chenier Plain the panic beach grasses (Panioum amarum) 

 and marsh grasses such as saltmeadow cordgrass and salt grass commonly in- 

 vade the dunes. 



Beach and dune management with vegetation is common in areas with sig- 

 nificant dune structure. It can be divided into two parts: (1) stabiliza- 

 tion and maintenance of naturally occurring dunes and (2) creation and sta- 

 bilization of protective dunes where they are presently non-existent. The 

 creation of stabilized dunes by vegetation is preferable to using mechani- 

 cal structures. 



Transplanting techniques are well developed and recomended for areas 

 adjacent to the beach berm and for critical areas — sites subject to erosion 

 (Coastal Engineering Research Center 1973). The vulnerability of a site 

 to erosion determines the transplant spacing and culm number. The more 

 vulnerable the area, the greater the number of culms per transplant and 

 the closer the spacing required to insure successful stabilization. If a 

 dense first year growth is desired, the transplant spacing should be less 

 than 13 inches. Transplants on flat to moderate slopes may be accomplished 

 by mechanical transplanters on a tractor, while steeper or irregular slopes 

 must be planted by hand. 



Plant spacing and sand movement must be considered in determining the 

 overall dune morphology. If the plant spacing is dense and there is only 

 a small amount of sand moved for trapping, the bulk of the sand will be 

 contained along the seaward edge of the dune and a narrow-based dune is 

 formed. If the plant spacing along the seaward edge is less dense given 

 similar conditions of sand movement, the result will be a wider based dune. 

 However, it should be recognized that the effectiveness of less dense plant 

 spacing along the seaward edge of the dune is limited by the rate of plant 

 growth. An additional factor is wind direction. In the case of onshore 

 winds, the seaward edge of the dune traps nearly all of the beach sand. 

 Offshore winds blowing over unvegetated areas landward of the dunes result 

 in materials being trapped at the landward edge of the dune. The annual 

 trapping capacity of panic grasses and sea oats is between 1 and 3 yd^ per 

 linear foot of beach, possibly exceeding this rate in some cases. It is 



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