WET LANDS OF SOUTHERN LOUISIANA. 39 



The advantages of the large district over the small one are: 

 (1.) Low cost of Levees per acre of protected land; 



(2) Possibility of using natural ridges in part for levees; 



(3) Possibility of using natural bayous and lakes as part of the interior 

 drainage system ; 



(4) Use of efficient machinery due to more continuous operation of the 

 pumping plant; 



(5) Low first cost, per unit of area, of pumping plant due to centralization 

 of equipment and smaller relative capacity ; 



(6) Low unit operating charges on pumping plant. 



The benefit of low lifts on the smaller districts is offset by the advantages in 

 using more efficient machinery for the high lift's on larger districts and the 

 less cost per acre of machinery. Unit labor charges for plant operation also 

 are much less on the larger districts. Although the haul to water transporta- 

 tion on large districts is necessarily greater, with larger interests involved, 

 good roads can be built, and maintained economically. Since the cost of levee 

 per acre of reclaimed lands is so much less on a larger district, a better class 

 of levee can be constructed, resulting in an increased margin of safety. While 

 the small district can take advantage of natural ridges at times, this usually is 

 possible only on one or two sides, and only in rare cases can the small district 

 include natural bayous and lakes as reservoirs. The advantages, in the case of 

 the small district, of the small capital involved and the earlier return on the 

 investment may be offset easily by the increased cost per acre for construction 

 of levees, canals, and pumping plant. The operation and maintenance charges, 

 which are a perpetual tax on the land, also are higher on the small district, and 

 from the standpoint of the individual owner and cultivator of the land the 

 advantage is all with the large district. 



Just what is the most economical size of district has not yet been deter- 

 mined ; it is a matter that is greatly affected by local conditions. How- 

 ever, it is the consensus of opinion among engineers engaged in this work 

 that districts containing less than 2,000 acres are not at all desirable. An 

 area of about 5,000 acres has been found very satisfactory under average con- 

 ditions. Where large lakes and bayous can be included as reservoirs and 

 drainage channels and natural ridges can be taken advantage of for levees, a 

 district well may be much larger than 5,000 acres. 



LEVEES. 



The location of a levee influences its design, construction, and maintenance, 

 as well as its usefulness to the district. Unlike levees along, our rivers, those 

 along the average reclamation district in this section have not been located 

 according to the topographic conditions, but rather according to property or 

 land lines. This has usually resulted in regularly shaped districts and mini- 

 mum length of levee for area inclosed ; but the cost of construction and main- 

 tenance per unit of length has often been much greater than if some atten- 

 tion had been paid to topography. Throughout most of the wet prairie there 

 are winding bayous that have along them solid ridges of silt that average 

 from 1£ to 2 feet above general ground surface. In other places the bayous 

 are filled in. entirely, and there have been left ridges of silt having widths of 

 from 200 to perhaps 1,200 feet, with the usual elevation of 2 feet. If the levee 

 be located on a solid ridge, the material will be more stable and impervious 

 and the levee can be made of less cross-sectional area than would be necessary 

 if it were located in the soft prairie. Construction, also, will be easier and 

 cheaper and the expense of maintenance much less. Where levees are to be 



