54 BULLETIN 652, U. S. DEPARTMENT OF AGRICULTURE. 



Although as regards first cost alone it appears that the larger plant and small 

 reservoir should be used, other factors enter into the problem. With larger 

 canals the lift would be less, due to the flatter surface slope of the water flow- 

 ing to the plant. When pumping from the larger canal the service of the pump- 

 ing plant would be less intermittent, thus saving considerable of the fuel neces- 

 sary for firing up the plant. The rate of interest on the cost of the plant would 

 be the same and the expense of clearing the canals of accumulated silt would be 

 more or less independent of the size, at least within reasonable limits. In re- 

 moving the run-off from a given storm the small plant would have to operate 

 longer, thus increasing the labor charges. The proper weight to give each of 

 these factors would depend on the local conditions in the district in question. 



LOCATION, DESIGN, AND CONSTRUCTION OF PLANT. 



Theoretically, the plant should be so located that the water in coming to 

 it will travel the minimum length of reservoir canal. This condition will 

 usually be met if the plant is placed in the center of the district and dis- 

 charges through a leveed outfall canal to some bordering lake or bayou. In 

 practice, however, the plants ordinarily are located on one side of the tract 

 and on some navigable lake or bayou. This greatly facilitates the transpor- 

 tation of heavy machinery during the erection of the plant, as the ground 

 usually is much too soft to allow the hauling of heavy ioads. Fuel, also, can 

 then be transported cheaply. If the tract has any considerable slope the 

 logical location of the plant is in the lowest part. However, this part often 

 is very soft, and to secure foundation it may be advisable to locate in some 

 higher and more stable portion. As pointed out in the discussion of levees, 

 there are frequent ridges of silt winding through these swamps, and often a 

 plant can be located .on one of these solid ridges. While it would be necessary 

 to use a great many piles under the foundation in either case, the number can 

 be reduced if the plant is located on a ridge. 



The foundation under both the machinery and the building of a pumping 

 plant should be of concrete, well supported by piling. A plan of the foundation 

 under the plant at Gueydan already has been shown (fig. 10) and is a good 

 illustration of a foundation in this character of soil. The foundation under the 

 plant on the Des Allemands drainage district, already illustrated (fig. 8). also 

 is a good one. It will be noted on both these plans that the foundation is sur- 

 rounded by sheet piling and that under the center of the Des Allemands plant 

 a line of sheet piling has been driven and extended into the concrete. In these 

 soft soils such precautions are necessary. The engine and pump are usually 

 mounted on the same block of concrete, so that any subsequent settlement can 

 not throw them out of line. 



While buildings to inclose the machinery should be durable' and of fireproof 

 construction, they are not called upon to protect the machinery and attendants 

 from low winter temperatures. A frame of structural steel covered with heavy, 

 corrugated, galvanized iron answers the purpose very well, although in one 

 case a brick building has been erected. These buildings should be capable of 

 resisting the action of the tropical hurricanes, for it is at such times that the 

 need for the plant is greatest. 



The selection and arrangement of machinery in centrifugal pumping plants 

 have been discussed in detail in publications of the department. 1 While the 

 local conditions considered in those publications are somewhat different from 



1 I'. S. Dept Agri., Dept. Bui. 304, contributed by Office of Public Roads and Rural 

 Eng. ; U. S. Dept, Agr., Office of Experiment Stations, Cir. 101. 



