54 BULLETIN 71, U. S. DEPARTMENT OF AGEICULTURE. 



these cases the crown is somewhat over 10 feet. The maintaining of a road on 

 a levee seems to aid in Iveeping ont muslirats and other bnrrowing animals, 

 bnt gradually decreases the height. The side slopes are usually quite flat, 

 being about 3 to 1. In very few of the levees had any preparation been made 

 for the base, either by clearing away vegetation or by cutting muck ditches. 

 "Where both the muck and subsoil were very soft, seepage through the base 

 was not noticeable, bnt where the muck was turfy in character nearly 

 all the levees developed seepage when the berm on the outside of the levee 

 was submerged to any considerable depth. Seepage appears to increase in vol- 

 ume as the muck in the levee decays and shrinks ; thus in some cases the older 

 levees were not keeping out the water as well as they did at first. It has been 

 necessary to cut muck ditches along many of these old levees to intercept the 

 flow of water through their bases. 



The majority of these levees were constructed with some form of dredge. 

 The unit price for material, measured in excavation, was in the neighborhood of 

 7 or S cents per cubic yard, depending on the amount of timber and stumps 

 encountered. It is always necessary to place more material in a levee than 

 the final cross section indicates, owing to subsidence of tlie base and shrinkage 

 of the material. This shrinkage will require from one and one-half to three 

 times as much excavation as the final volume of the levee. The unit cost of 

 levees will therefore vary from 12 to 25 cents per cubic yard; measured in 

 settled embankment. If the levee is brought to a regular cross section by 

 hand or machine work a small additional charge should be made; generally, 

 however, the embankments are not surfaced after the dredge work is finished. 



The natural growth of prairie grass soon covers the majority of the levees, 

 and some of them have been sown to Bermuda grass. The levees are often 

 pastured, and when this is done with care it affords an efficient and a profit- 

 able method of maintenance. 



DITCHES. 



The spacing of the ditches has been varied on the different districts accord- 

 ing to the nature of the soil. Some of these are spaced too far apart to give 

 adequate drainage, but, on the other hand, on none of the districts are the 

 ditches too close together for economy; that is, the land is in no case over- 

 drained. A spacing of 330 feet on newly reclaimed lands seems to be popular, 

 with the idea of making the spacing 165 feet when the land becomes more 

 impervious, due to the decay of tlie vegetable matter. The size of the ditches 

 is quite uniform and is usually ample, except where the ditches are too long. 

 The eflBciency of these small ditches as water channels is very low, for they 

 ai-e usually partly filled with weeds and grasses. As most of the land is flat, 

 flow is caused only by the piling up of drainage water in the ditch. A length 

 of about a quarter of a mile has been found to give satisfaction in flat land, 

 and when there is any considerable slope to the ground much longer ditches 

 have been used with entire success. The use of the 6 to 8 foot collecting ditch 

 to take the water from the laterals has not proved a success on the marsh- 

 land districts, the maintenance charges being too great. The percentage of 

 land taken up by these latei-al systems is usually between 2 and 3 per cent. 

 The cost of their excavation has been between 5 and 6 cents per cubic yard, 

 and with a spacing of 330 feet the cost of the ditches per acre has been 

 between $2 and $2.25. 



GROUND WATER. 



The ground water is controlled largely by the depth of the lateral ditches. 

 Even though the sub.soil be very fine grained and impervious, there is a consid- 

 erable lateral movement of the water, as was shown by measurement of the 



