LEVEES. 77 



to economy of material and capacity for protection. Its general direction should be 

 nearly parallel to that of the stream, but should avoid as much as possible exposure 

 to the most destructive and prevailing winds. The fitness of the foundation should 

 especially be regarded, and good high ground selected, free from creeks or sloughs. 

 Sharp angles are to be condemned, especially re-entering angles, because they make 

 basins in which the wind has full play to raise the water. When changes of direction 

 occur they should be made by a curve, uniting the two tangents." 



Section. The cross-section of a levee will vary with its location, the character 

 of the foundation upon which it is to be built, and the material of which it is to be 

 constructed. In exposed positions, where the waves are liable to make inroads, the 

 section of the levee must be greater and the slopes less steep than in those places 

 where wave-action is not expected, down to solid earth. Lastly, the material of which 

 an embankment is made will in a measure control its profile. If it is to be of sand or 

 light porous soil it will be much more liable to be washed and cut away than if built 

 of clay or gravel, and hence must have a greater thickness. 



In this country the most usual dimensions are 8 to 10 feet across the top or crown, 

 with slopes of 3 to i , an increase being made for levees built of sand, in which the width 

 sometimes reaches 15 feet on top with slopes of 5 to i. When the levees are high a 

 terrace or "banquette" is usually built on the land side for the purpose of obtaining 

 the necessary strength. This bench is about 20 feet in width, sloping off more grad- 

 ually than the main embankment, and is usually about 8 feet below top of the levee. 



The levees along the Po are generally from 23 to 26 feet on top with slopes from 

 2 to i, to 3 to i, and usually have two horizontal terraces on the land side. The dimen- 

 sions of course vary considerably with the conditions, in some places the top width 

 being reduced to 16 feet. When used for roadways, a custom which is quite general 

 there, the crown is of gravel. 



On the Rhine the levees have a top width of about 6 or 7 feet, with slopes of 3 to i. 

 These narrow crowns are doubled when it is desired to use them for wagon roads. 



In Prussia the levees along the Elbe have dimensions about the same as those on 

 the Rhine, with banquettes on the land side where the height renders additional strength 

 necessary. 



The tops of the Theiss levees rise about 5 feet above the highest flood-level, and 

 are about 20 feet wide, with slopes of 2 to i on the river side above the level of the 

 highest water, and 4 to i below that level, while on the land side the slope is 2 to i. 

 This slope is broken by a terrace 13 feet wide, placed about 3 feet below high-water 

 level. The Vistula levees in Prussia are from 12 to 16 feet in width at the crown, with 

 slopes of 3 to i on the river side and 2 to i on the land side. There is usually a ban- 

 quette having about the same width as the top of the levee. 



In Holland the sections vary greatly, according to location, material, and existing 

 conditions. They- are from 16 to 25 feet on top, with slopes of a J to 3$ to I. Those 

 built to withstand sea-waves are of course considerably more substantial than those 



