DRAIlSrAGE OF WET LANDS OF SOUTHERN LOUISIANA. 23 



In order better to explain the nature of the drainage problems encountered 

 and the reclamation methods employed, a detailed discussion of a number of 

 reclaimed areas will be given, and a summary of the results of all investigations 

 presented. The areas discussed are arbitrarily designated by numbers. These 

 examinations were made or completed during the spring of 1912, and the de- 

 scriptions refer to conditions at that time. 



EXPLANATION OF TERMS. 



Before proceeding with the discussion of the reclamation districts a brief 

 explanation of some of the technical terms hereinafter used will be given. 



By run-off is meant the water that flows over or through the ground to 

 drainage outlets. All run-off originates in precipitation ; therefore the latter is 

 the most important of all the factors that influence the rate of run-off, some 

 other controlling features being size, shape, topography, and geological structure 

 of the watershed, climatic conditions, and the character of the vegetation. 



In so-called gravity drainage districts the run-off is removed by gravity 

 through the main outlets. In pumping districts the run-oft" is collected at some 

 central point within the district and pumped over or through the levee. The 

 rate of run-off is expressed as a quantity of water removed in a unit of time. 

 This quantity of water can be conceived as a certain depth distributed uni- 

 formly over the entire drainage area. Similarly, the capacity of a pumping 

 plant is the quantity of water, expressed in a depth uniformly distributed 

 over the drainage area, that the pump can dispose of in a given time. As used 

 in the following discussion, the rate of run-off is expressed by the depth of 

 water, in inches, distributed uniformly over the drainage area, that passes 

 from the area in a period of 24 hours. Likewise, pumping plant capacity is 

 expressed in terms of a depth of water, uniformly distributed over the drainage 

 area, that can be removed by the plant in 24 hours of continuous operation. 

 Reservoir capacity also is represented by a uniform depth distributed over the 

 drainage area. The object of expressing the rate of run-off and the pump and 

 reservoir capacities in depths rather than in volumes per unit of time is to 

 arrive at a basis of comparison that is independent of the drainage areas. On 

 any particular tract, the area being known, these rates can of course easily be 

 reduced to cubic feet per second or to any other convenient unit. 



In a long period the total amount pumped would approximately equal the 

 run-off for that period, but for short intervals, as, say, 24 hours, the run-off 

 from an area might be much greater than the quantity pumped, the excess 

 being stored in the reservoir for subsequent pumping. 



AREA NO. 1, WAGGAMAN. JEFFERSON PARISH, LA. 



As shown in figure 4, this plantation, containing 2,600 acres, fronts on the 

 Mississippi River and extends back into the prairie swamp lands in the rear. 

 It is a typical example of one of the old river-front plantations which have 

 been extended to include a comparatively large area of wet prairie land. The 

 tract of swamp land, which makes up one-third of the present area of the 

 plantation, was included by the extension of the levees about 12 years ago. A 

 pumping plant was installed, and cultivation has been continuous since that 

 date. The area of prairie included was quite typical of those in this part of 

 the State, and was covered with a scattering growth of small willows and the 

 usual rank growth of prairie grass. Originally the muck was about 3 feet 

 deep, although at present, after 12 years of cultivation and decay, it is well 

 compacted and has subsided or shrunk until it now averages 2i feet lower than 

 it originally was. The total fall in the surface of the ground from the front 



