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



although it would be better if the levee were smoothed off, seeded to Bermuda 

 grass, and pastured. This will aid in closing up the cracks that form through 

 the gradual shrinking of the material. In certain cases it may become necessary 

 to plow and harrow the levee in order to close up these cracks. If this is not 

 done, and if a rapid rise of the water outside the district occurs after a pro- 

 longed dry period, the seepage through the body of the levee will be very great. 

 In certain cases this seepage through shrinkage cracks has overtaxed the 

 capacity of the pumping plant. The grazing of the levee provides a cheap and 

 profitable method of maintenance and will discourage the action of burrowing 

 animals. 



INTERIOR DITCa SYSTEMS. 



Rainfall and seepage cause an accumulation of water within the levee dis- 

 trict that must be collected by a system of ditches and canals, led to a central 

 point and discharged over the levee by means of pumps. Numerous arrange- 

 ments of ditch systems have been used with varying degrees of success, depend- 

 ing on how well the work was executed and maintained. The best of present 

 practice is to make this system consist of small ditches which can be cut and 

 maintained by hand, discharging into reasonably large canals which can be 

 cut and maintained by means of a dredge. The use of intermediate-sized 

 ditches, say, 6 to 8 feet wide and 5 or 6 feet deep, has not proved successful 

 on these districts. Since such ditches are free from water most of the time, 

 grass grows very readily in the bottoms. Moreover, they are too large to be 

 cleaned by hand easily and are too small to allow the use of a dredge. 



Field Ditches. 



On the typical wet-prairie reclamation district the land is so nearly level that 

 a regular layout of field ditches is desirable rather than a location designed to 

 take advantage of such slight surface slopes as may exist. The ditches should 

 be cut in parallel lines and at such a spacing as will correspond with the char- 

 acter of the land. As shown in Table I, the spacing of ditches has varied from 

 100 to 330 feet. The degree of drainage required in these soils depends some- 

 what on the crop. Where rice is grown, a spacing of 330 feet has proved ample 

 for soils in southwestern Louisiana. Where very valuable truck crops are to 

 be grown, a spacing even less than 100 feet might be required. In general, a 

 spacing of about 200 feet has been found satisfactory for general field crops, 

 such as corn and sugar cane. As the lands are cultivated and compacted, and 

 the loose vegetable material in the soil decays, a spacing of less than 200 feet 

 may be necessary. A ditch 4 feet deep, 4 feet wide at the top, and about li feet 

 wide at the bottom has been found to be the most economical to cut and main- 

 tain by hand. Ditches of this size are of ample capacity, unless they become 

 choked with weeds or are required to bring the water too far. Since the land 

 is practically flat, flow in such a ditch is caused only by the piling up of the 

 water in the upper end of the ditch. If the ditch is too long, this will bring the 

 water too close to the surface of the land. In practice it has been found that 

 in flat land such ditches can be made one-fourth mile long with good results, 

 and they have worked fairly well in a few cases at a length of one-half mile. 

 However, this latter length is not recommended, as the ditch must be main- 

 tained in almost perfect condition in order to give satisfactory drainage. In 

 most cases where the small field ditches are one-half mile long they have not 

 proved satisfactory. 



While this type of ditch can be cut in this section with hand labor for from 

 5 to 7 cents per cubic yard, a large proportion of the work has been done with 



