CONSTRUCTION OF COAST DUNES 179 



According to Grandjean: 



" In the Gironde the palisade was established quite close to high tides ... but in 

 the Landes on the contrary it was 490 feet from high tide. This paUsade having been 

 successively raised until the dune attained an elevation of 20 to 26 feet and the talus 

 becoming too steep they estabhshed (5 feet to the west) a cordon of fagots at the foot 

 of the talus." 



This lessened the steepness of the slope and was an excellent modifica- 

 tion. The tendency has been to build the artificial dunes farther from 

 the sea, up to 820 to 980 feet. In 1851 the artificial barrier or coast dune 

 was constructed as follows: 



"At 165 to 260 feet from the high tide mark, parallel to the shore that is to-day per- 

 pendicular to the direction of the wind, a palisade is built of joists 4.7 inches wide and 

 1.2 inches thick; these joists are deeply imbedded in the sand with a projection of 3.3 feet 

 above the soil; they are spaced 0.8 to 1.2 inches from each other. After each storm 

 the sand, driven by the wind, accumulates in front of the palisade and piles up on the 

 other side through the spaces left between the joists; according to the size of the particles 

 the equilibrium between the piles on the two sides is more or less readily established. 

 This operation is repeated until the artificial dune is 33 to 39 feet high above high tide. 

 The theory of this method is that the wind is harnessed by man to do his work. The 

 slope is quite rapid on the talus facing the sea and the best grade or reUef is always an 

 important problem which must be studied locally. The surface is fixed with maram 

 grass (gourbet, calam agrastis arenacea) secured by sowing or by root suckers. The 

 maintenance work consists chiefly of repairing the breeches made by the sea or wind." 



To-day the profile of these artificial dunes is being reversed, and the 

 slopes are gently inclining toward the sea and abrupt on the land side, 

 since it has been found by experiment that this gives better results. 



"This new profile is secured by placing (parallel to the shore) successive lines of little 

 hedges about 24 inches in height built of pine branches at the foot of which the sand 

 accumulates. The skill consists, according to the form of the shore line and the prog- 

 ress of the sand, in placing these obstacles at the desired point to assist the dune to 

 form its ridge line at such a distance from the shore that the slope can extend on the 

 most practical incline. These very cordons, coupled with the maram grass sowing 

 without a branch cover, can stop and hold in check the 'whistle-wind' and the ravines 

 that the wind bores in the dune. . . . 



"Moreover, it is marvelous to see how experienced foresters know how to use the 

 growth to model the dune sand, something so mobile and capricious; where the (de- 

 sired) profile has been secured they use the maram grass to fix these points, or on the 

 contrary, pull out or thin the plant when they wish the wind to remove the piles of sand 

 or mounds which have become useless or troublesome. Frequently hedges parallel 

 to the coast are flanked with dikes whose direction is perpendicular to them, when these 

 can be further subdivided into crow's feet or reverse dikes. 



"When winding shores with sharp points are exposed to very violent wind, a care- 

 ful study of the situation only can determine the places where defense work must be 

 established, and what direction to give them. . . . Finally, on points where the sea 

 in eroding its shores and breaks into waves without depositing sand the material be- 

 comes scarce . . . the force of the waves is reduced by the erection of a forest of sohd 

 stakes driven into the sand and called break-water (bris6-lame) . The tamerisk, with 

 its long flexible branches, renders the greatest service in consolidating all these dead 



