RECLAMATION OF LOUISIANA WET PRAIRIE LANDS. 433 



LEVEES AND SEEPAGE, 



Sometimes the natural embankment or high ground adjacent to 

 the bayou or river makes a levee unnecessary along the stream side 

 of the plantation, but ordinarily the other three sides need such pro- 

 tection, wholly or in part, the height of the levees depending in large 

 measure upon the proximity to the Gulf and upon the elevation of 

 the land surface respective to the high water in times of flood. Ordi- 

 narily the levees do not require such careful construction as those 

 along streams subject to frequent and prolonged floods where the 

 water often stands against the embankment for long periods, nor is 

 it always so necessary to clean the entire levee site as in this latter 

 case. It is always well, however, to remove all coarse vegetable 

 matter, and a plowing up of the site is very desirable, in order to 

 insure a good bond. The general specifications for levee construction 

 and maintenance have been given in a previous publication of this 

 Office." A muck ditch 2 or 3 feet in width and about 2 feet in depth, 

 and approximately on the center line of the proposed levee, should be 

 constructed, in order to insure against excessive seepage. Such 

 seepage is liable to be the minimum in the fine close-textured silt soil 

 back in the marshes. In the case of the Gheens plantation. La 

 Fourche Parish, 2 parallel muck ditches spaced 25 feet apart are used 

 under the levee. 



Shrinkage of the levee should also be taken into account, and expe- 

 rience would indicate that levees in these soils built by means of 

 shovels or wheelbarrows shrink about one-fifth of their gross height, 

 while those constructed by wheel scrapers shrink one-eighth in height. 

 Where an excavating machine is used in dry material the shrinkage 

 is approximately one-sixth and where excavated material is wet it is 

 probably not more than one-tenth. In the latter case the spoil gen- 

 erally being from a greater depth and being well compacted during 

 the construction usually insures less seepage than where hand work 

 is performed and where the levee is constructed from the looser, 

 coarser material nearer the surface. In order to prevent excessive 

 seepage, it is preferable in constructing the levees to excavate the 

 canals on the outside, leaving a sufficiently wide berm to prevent the 

 spoil from sloughing back into the ditches. Unless care is exercised 

 this is especially liable to occur in the soft prairie lands. The levees 

 require for the first few years frec|uent additions in order to keep 

 them to the required height, unless, when first constructed, shrink- 

 age has been allowed for. In order to maintain them with as little 

 care as possible, it is well to have them sodded to Bermuda or some 

 native grass, which not only prevents them from washing, but alsa 



"U. S. Dept. Agr., Office Expt. Stas. Bui. 158, Sep. 9. 

 46045°— 10 28 



