60 BULLETIN 71, U. S. DEPARTMENT OF AGRICULTURE. 



AREA OF THE DISTRICT. 



Although in many localities topography has a large influence in fixing the 

 area of a reclamation district, there are many large bodies of land of such a 

 character that the size of the unit would be determined almost entirely inde- 

 pendently of topographic conditions. In order to make clear the conditions 

 governing the determination of the most desirable size of unit, the respective 

 advantages of the small and large districts will be enumerated. The principal 

 advantages of the small unit are : 



(1) Short internal drainage canals with small losses of head and the conse- 

 quent low lift. 



(2) Short haul to outside water transportation. 



(3) Small area affected in case of failure of protection levee. 



(4) Small capital involved. 



(5) Short time required to place land under cultivation and early realization 

 on investment. 



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 pump- 

 ing 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 lifts on larger districts and the 

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

 would be much less on the larger districts. Although the haul to water trans- 

 portation on large districts would necessarily be greater, with larger interests 

 involved good roads could be economically built and maintained. Since the 

 cost of the levee per acre of reclaimed land would be much less on a larger 

 district, a better class of levee could be constructed and breaks prevented. 

 While at times the small district could perhaps take advantage of natural ridges, 

 this would usually result in too much irregularity in shape and only in rare 

 cases could the small district include natural bayous or lakes as reservoirs. 

 The advantages, in the case of the small district, of the small capital involved 

 and the earlier return on investment might easily be offset by the increased 

 cost per acre of construction of levees, canals, and pumping plant. Just what 

 is the most economical size of district has not yet been determined; it is a 

 matter that would be greatly affected by local conditions. However, it is the 

 consensus of opinion among engineers engaged in this work that districts con- 

 taining less than 2.000 acres are not at all desirable. Most of the districts 

 now being planned are several times larger than this. One of the newest dis- 

 tricts, and the largest yet planned, lies just across the Mississippi River from 

 the city of New Orleans and contains 37.750 acres. 



LEVEES. 



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

 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 minimum length of 



