40 BULLETIN 652, U. S. DEPARTMENT OF AGRICULTURE. 



built to protect areas of marsh land on the immediate coast line, a strip of 

 land at least a quarter of a mile wide should be left as a foreshore to break 

 the force of the wave. Where the exposure is particularly great, this strip of 

 land should be wider. 



If the levee be located on firm land and the land outside the levee never is 

 flooded for more than a few days, it will, in some cases, be advisable to dig 

 the canal from which material is taken for the levee on the inside of the 

 district and to utilize this canal as a drainage channel. In such cases the 

 berm should be especially wide, at least 20 feet. In general, this type of 

 construction is not recommended. If the levee canal be placed on the outside 

 of the district it can be utilized for navigation. 



The design of the levee will depend largely on local conditions. Its top 

 should be from 2 to 4 feet above the highest stages of water in the sur- 

 rounding lakes and bayous, depending on the area of land protected and the 

 probability of previous high-water marks being exceeded. Where the water 

 to be kept out is due to storm tides in the Gulf, the height of the levee should 

 be determined only after very careful investigation of all surrounding condi- 

 tions has been made and the probable highest stage estimated, taking into 

 consideration the local conditions as outlined under the section on Tidal 

 Overflow. If the levee is located in an exposed locality its top should be 

 about 4 feet above the estimated highest water. A minimum height of about 

 4 feet should be used through the soft prairie section, as anything less is 

 not likely to prevent seepage satisfactorily ; for when located on a ridge the 

 water will stand against a levee only for short periods, while if located in a 

 soft prairie the water will be in continuous contact with the lower foot or 

 two of the levee. In places exposed to strong wave action the height should 

 be sufficient to provide for the break of the waves; in addition, some pro- 

 vision should be made for protecting the levees from their erosive action. This 

 protection could be secured by planting willows some distance in front of the 

 levee. 



Where the levee is located on a ridge the top width may safely be made 4 

 feet, with side slopes 2 to 1. A levee of this type is often built with wheel- 

 barrows, and although the unit cost for this method is quite high, being about 

 18 cents per cubic yard, the total cost is considerably less than if the work were 

 done with the usual floating dredge. Yard for yard, the dredge would, of 

 course, handle the material much cheaper, but the excavation would be more 

 than would be necessary for the levee. This objection would be overcome if 

 the dredge were building a levee along the bank of a bayou of sufficient depth 

 to float the machine, or if a reservoir canal were being excavated within the 

 district, the waste bank to be used as a levee. 



Where the levee is located in the soft prairie the top width should average 

 about 6 feet. The side slopes should be about 3 to 1 ; in fact, if the material 

 is very soft it will not take a much steeper slope than this during construc- 

 tion. As the material always becomes more stable after being placed in the 

 levee, no trouble should be expected from slides after it begins to dry in place. 



The berm along the base should be at least 15 feet wide. Where the soil 

 is exceptionally soft this should be made as much wider as practicable, at 

 least 20 feet. The width of berm will of course depend somewhat upon the 

 nature of the machinery used in construction. 



Some type of floating dredge should be used in the construction of most 

 levees. In heavily timbered sections, or where old submerged stumps are nu- 

 merous, the dipper dredge will work to the best advantage; but in the open, 

 grass-covered prairie the orange-peel-bucket dredge has many advantages. 



