CONSTRUCTION OF COAST DUNES 

 TABLE 18.— AREA OF FRENCH DUNES 



177 



The dune areas in the Gironde and Landes are about equal. The 

 maritime pine covers a large area outside the dunes. There is a total 

 forest of 1,656,630 acres in the Lot-et-Garonne, Landes, and Gironde 

 divided as follows : 



Oumership Acres 



Private and communal forest 1,510,549 



Communal forest under State control 17,411 



State forest 128,670 



1,656,630 



By 1899 there were 140 miles of artificial barrier dunes in the Landes 

 and Gironde Departments alone, the first barrier dune having been 

 constructed in 1833 (see p. 178). 



FIXING THE SAND 

 Construction of Coast Dunes. — It has already been seen that the 

 ocean sand, if unchecked, drifts inland and submerges everything of 

 value in its path. The theory of fixing or stabihzing the sand is to secure 

 and maintain the following conditions. 



Desired conditions Objective 



Gradual shelving beach ... To allow the waves to break their force without eroding or 

 washing the dry sand. 



Barrier dune To dam the drifting sand. 



Grass or vegetable cover . . To maintain the sand in place on and around the barrier 

 dune. (See Fig. 15.) 



Forest protection belt To help maintain the sand in place and to protect the 



merchantable stands from the effects of the wind. 



The underlying principle is as follows: ^^ 



"Every fixation system is founded on the following principle : In the mass of bare sand 

 susceptible of being eroded by the wind, the transport takes place grain by grain. . . . 



10 This is substantially the same area as was reported in 1822; in 1800 Bremontier 

 had estimated it at 271,815 acres and at over 281,420 acres in 1803, while Villers had 

 grossly overestimated the area in 1779 at 878,913 acres. 



" Boppe, pp. 478-481. 



