stoppage^ and less and less diversion of sand. These barriers require 

 frequent changing or cleaning. The dune development behind diversion 

 fences is shown in Figure 135. 



I4.270 Oil penetration ccats of hot crude oil may be used to 

 stabilize the face of the dune and cause the dune to widen. Penetration 

 is deeper when the upper few inches of sand are dry. Oiling is expensive 

 and special equipment is necessary for highest efficiency. Oiling is 

 effective for only a few years and must be repeated frequently. Oiling 

 increases the saltation coefficient of material flowing over the surface. 

 The sand blows up and over the top, depositing in front of the slip face 

 in successive advancing fill increments. This widening of the dune con- 

 tinues until a streamlined body is built downwind from the paved face. 

 The entire mass is permanently stored for as long as the oiled surface 

 remains intacto Figure I36 shows the successive steps of dune development 

 behind an oiled surface. 



I1.28. Dune Stabilization . - After protective dunes have been formed 

 they should be stabilized with vegetation. This is expensive in the 

 beginning but minimizes future difficulty. The most satisfactory plants 

 are long lived perennials =, vjith extensive root systems^ that spread 

 rapidly either vegetatively or by seed or both, and maintain surface 

 growth even though sand is accumulating around them to increasing depths. 

 Such plants are not numerous but in practically every section a few 

 satisfactory ones are obtainable at reasonable costs. 



l!.29. Usually grasses are available and can be transplanted from 

 naturally established plantings. Transplanting is most satisfactory by 

 using small clumps |- to 1 inch in diameter ^ setting about 8 to 10 inches 

 deep in staggering rows with plants in rows about I8 inches apart. 

 Staggering the rows prevents direct wind action over long areas and 

 offers more opportunity to hold sand than straight line planting. Dunes 

 are low in fertility and contain practically no organic matter. 

 Nitrogeneous fertilizers are stimulating and while net effective very long 

 in the sand^ they are of benefit in inducing vigor and enabling newly set 

 plants to get firmly established the first year. The use of coarse 

 fertilizers as manure is generally not practicable because its effect 

 is so slow that little of its value would be realized, 



14.30. Brush barriers may be used effectively to control the sand 

 on newly filled areas while grasses , shrubs, or trees are gaining a 

 foothold. These barriers are usually built in rows k feet apart, cross- 

 wise with the prevailing wind^ about 2 feet high^ 1 to 2 feet wide, and 

 anchored firmly with stakes. Any kind of brush will suffice, although 

 evergreen material is most satisfactory, 



U3I, Covers for Vari ous Regions. - In the Great Lakes region, the 

 best grasses for use in sand binding are European beach grass, long- 

 leafed reed grass, European dunegrass, Redfield grass, and Northern 

 Wheatgrass. All are native to the region except European beach grass 



20it 



