WET LANDS OF SOUTHERN LOUISIANA. 45 



PUMPING PLANT. 



The drainage of low-lying wet lands by means of pumps is described in a 

 publication of this office. 1 The bulletin discusses the general practice of land 

 drainage by means of pumps and deals especially with conditions in the upper 

 Mississippi Valley. The general nature of this method of drainage in southern 

 Louisiana is much the same as described in that bulletin, but there are many 

 differences in detail that deserve mention. These differences affect chiefly the 

 capacity and operation of the pumping plant. 



Necessaey Capacity of Plant. 



The general method of operation of plant in southern Louisiana is far dif- 

 ferent from that in the northern latitude, so before discussing in detail such 

 rainfall and run-off records as are available it might be well to describe the 

 usual method of operation. In southern Louisiana farming operations are con- 

 ducted every month in the year. While general field crops are growing only 

 about 9 or .10 months, the field must be kept sufficiently well drained to permit 

 cultivation at any time. The bulk of the heavy plowing is done during what 

 are ordinarily called the winter months. The need of the pumps, therefore, is 

 more or less continuous — that is, the run-off at any time of the year must be 

 taken out promptly. 



During the first few years after construction the maintenance charges on 

 reservoir canals are quite high. A certain amount of bank caving occurs, and 

 a large quantity of semifluid mud comes in through the field ditches from the 

 soft land. The velocity of flow in the canals is not sufficient to transport any 

 appreciable amount of this soft mud to the pumping plant. Unless the water 

 is lowered very slowly when the pumps are first started, the tendency of the 

 soft subsoil to flow into the canals will become apparent. In one case where the 

 water was lowered rapidly the canal became several feet narrower and shal- 

 lower within a week or two. While in this case the spoil banks were too close 

 to the sides of the canal, and no doubt contributed to the rapid shrinkage of 

 section, the shrinkage was due mostly to a rapid lowering of the water. Canals 

 cut by hydraulic dredge will not be so susceptible to shrinkage, as the weight of 

 the excavated material does not rest on the banks. 



This rapid filling of the canals when the land is first drained makes it good 

 practice to excavate the canal somewhat larger than is desired for the perma- 

 nent section. If this be done, the canal will not require cleaning until the land 

 has had time to solidify and the soft mud has stopped coming in from the small 

 ditches. While the canal can then be cleaned with either a floating dipper or 

 orange-peel-bucket dredge, the best way is by the use of a hydraulic dredge. All 

 overhanging and unstable banks should be sloped by hand in advance of the 

 dredge work ; this material then can be taken out along with the soft material 

 in the canal bottom. The chief objection to the use of the hydraulic dredge for 

 this clean-out work is the effect of the water and soft mud on the growing crops 

 along the canal. To avoid this damage a small excavator mounted on skids 

 along the side of the canal has been used very successfully. By keeping the 

 canal practically empty of water, the soft mud will solidify enough to allow it 

 to be taken out by means of either an orange-peel or clam-shell bucket handled 

 by the excavator mounted on the bank. If this cleaning of the canals is done 

 after they have been cut and the land well drained for three or four years, 

 further cleaning will not be necessary for a long term of years. Because of 



1 U. S. Dept. Agr., Department Bulletin 304, contributed by Office of Public Roads and 

 Rural Eng. 



