DRAINAGE OF WET LANDS OF SOUTHERN LOUISIANA. 61 



ievee for area inclosed, but the cost of construction and maintenance per unit 

 of lengtli has often been much greater than it would have been if some atten- 

 tion had been paid to topography. Throughout most of the wet prairie there 

 are winding bayous that have along them solid ridges of silt that average 

 from 1| to 2 feet above general ground surface. In other places the bayous 

 are entirely filled in and there have been left ridges of silt having widths of 

 from 200 to perhaps 1,200 feet, with the usual elevation of 2 feet. On small 

 districts it is usually impracticable to take advantage of these ridges to any 

 great extent, as to do so would make the shape of the district too irregular, 

 but on larger districts the straighter ridges can be chosen, as irregularity of 

 outline is not so large an item. If the levee is located on a solid ridge the 

 material will be more stable and impervious and the levee can be made of less 

 cross-sectional area than would be necessary if it were located in the soft 

 prairie. Construction will also be easier and cheaper and the expense of 

 maintenance will be much less. 



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

 should be above storm tides and the highest stages of water in surrounding 

 lakes and bayous from 1 to 3 feet, depending on the size of the district and the 

 probability of previous high-water marks being exceeded. 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 provision 

 should be made for protecting the levees from the erosive action of the waves. 

 This protection might well 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 it would be if 

 the work were done with the usual floating dredge. Yard for yard the dredge 

 would, of course, handle the material much the 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 exca- 

 vated 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 

 construction. • 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 of the levee should be at least 10 feet. Where 

 the soil is exceptionally soft this should be made as much larger as practicable, 

 at least 15 feet, and it will be better if conditions permit its being made 20. 

 The width of berm will, of course, depend somewhat upon the nature of the 

 machinery used in construction. Where the levee canal is on the inside of a dis- 

 trict, special effort should be made to leave a wide berm. 



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

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

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

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

 Owing to the longer boom and narrower hull, the latter type of dredge is able 



