2. Use . 



Coastal barrier dunes are valuable to coastal protection in several 

 ways. Continuous barrier dunes serve as flexible barriers to storm 

 surges and waves, and are of particular value in affording protection to 

 low- lying backshore areas and in helping to preserve the integrity of low 

 barrier islands. For example, adequately stabilized and carefully pro- 

 tected foredunes play a significant role in the sea defenses of Holland 

 (Adriani and Terwindt, 1974). Where there is an adequate natural sand 

 supply, dunes provide protection more effectively and at a lower cost 

 than a seawall. 



Well-developed barrier dunes perform another important function by 

 providing stockpiles of sand to nourish the beach during storm attack. 

 Storm waves erode sand from the berm and foredune, much of which is 

 deposited immediately offshore in a bar formation, which allows the 

 beach profile to adjust to the energy of the storm (Fig. 5). In the 

 absence of the dune sand reservoir, sand for storm profile adjustments 

 must come from either the shore behind or the beach. In a stable beach- 

 dune system, sand removed from berm and dune by storms is returned to the 

 beach and berm by calm weather between storms. Thus, it is available to 

 rebuild the dune, a necessary process in maintaining a dynamic equilib- 

 rium within the beach-berm-dune system. Coastal dunes are also used for 

 water storage and recreation, and are highly valued as wildlife habitats. 



The use of dunes must be carefully controlled, and their management 

 should always include provisions for repair and restoration, as required. 



II. DUNE BUILDING 



The creation of new barrier dunes or the rebuilding of damaged or 

 incomplete foredunes may be done (a) mechanically, by moving sand into 

 place by truck, bulldozer, pipeline dredge, etc., and grading it to 

 suitable form, or (b) by trapping blowing sand by means of sand fences 

 or vegetation or a combination of these, where sand supply and wind 

 pattern permit. The latter method utilizes natural forces to create 

 dunes in the same way they develop in nature. Man speeds up and guides 

 the natural process. When this can be done, it is usually the most 

 economical method. The natural way tends to discourage the placement 

 of dunes in inappropriate or unnatural locations and is aesthetically 

 pleasing. 



1. Sand Movement . 



Sand grains are transported by wind in three ways (Bagnold, 1941) : 

 (a) in suspension; (b) by saltation, bounced along as the impact of 

 falling grains dislodges others; and (c) as bedload or surface creep, 

 rolled across the surface. Since movement in suspension may be ignored 

 except in the case of very fine sands or extremely high winds, sand 

 accumulation methods are designed primarily to control surface creep 

 and saltation (Fig. 6). 



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