DRAINAGE OF WET LANDS OF SOUTHERN LOUISIANA. 39 



of the tract the berm along the outside of the levee is smaller and averages 

 about 5 feet in width. As ditches do not parallel this levee except on one side, 

 and then not closely, the small width of berm should not prove a serious defect 

 as far as seepage is concerned. 



As stated on page 37, no muck ditch was cut in the base of the levee, and at 

 ordinary stages of water no large seepage was apparent. However, during the 

 high water that affected area No. 3 the levee leaked badly, and, as was the case 

 in area No. 3, the water seemed to come through the base where the layer of 

 muck occurred, rather than through the body of the levee itself. This defect 

 was remedied by cutting a ditch along the slope of the levee and filling it with 

 material dredged from the bottom of the canal. This not only cut off seepage 

 through the base of the levee, but added somewhat to the cross-sectional area. 



Resebvoie Canals. 



Owing to the size of this tract it was necessary to cut reservoir canals into 

 the interior to give outlet to the system of laterals. This rather extensive length 

 of canals gives a larger reservoir capacity than is had in any of the other 

 districts of this vicinity. Between the surface and a distance of 4 feet below 

 these canals have a capacity of 0.40 inch of water over the entire area. It is 

 possible for the pumping plant to lower the water below this level, but under 

 ordinary circumstances this is approximately the level to which the water is 

 reduced. The added depth of reservoir (the canals are nearly all over 6 feet 

 deep) will be of service in reducing the velocity of flow in the canals during the 

 time of pumping and also in keeping their bottoms covered with water. This 

 last feature will in a measure prevent the growth of weeds and grass and the 

 consequent choking of the canals. In December, 1911, these canals were quite 

 badly filled with a deposit of soft mud, 2 and even 3 feet having been deposited 

 in places since the cutting of the canals some two years previous. This deposit 

 is quite rapid during the first year of drainage. It is due partly to the wash 

 from the laterals, but also to the crumbling and the sliding of the sides of the 

 canals. The sliding is especially great when water is lowered too rapidly when 

 the district is first pumped out. By taking the water out very gradually it has 

 been found that, even when the canals have been cut in very soft material, any 

 great amount of sliding of canal banks can be avoided. In the softest portions 

 of the prairie it has been found that there is a tendency for the surrounding 

 mud to flow toward the canals when the water is lowered for the first time ; the 

 walls of the canals may continue to be even and unbroken, but the canals do 

 not remain as wide nor as deep as they were before the water was lowered and 

 this flow began. The material on this tract was too solid for any considerable 

 amount of flow to be apparent. During the early part of the month of Decem- 

 ber, 1911, an 8-inch hydraulic dredge was started in these canals to remove this 

 deposit of mud. It was found desirable on the larger canals to replace the 

 hydraulic dredge with an orange-peel-bucket dredge. By cutting into the harder 

 underlying material it was possible to remove most of the soft mud from the 

 bottom of the canal. This redredging of interior canals seems to become neces- 

 sary from two to four years after they are first cut. 



The reservoir has thus far given satisfaction in the reclamation of this tract. 

 The increase of lift during the operation of the pumps, due to the slope of the 

 water surface, is quite small. The greatest length of canal tributary to the 

 pumping plant is about 1\ miles. The greatest length of drainage channel that 

 the water travels is nearly 3 miles. 



