DRAINAGE OF WET LANDS OF SOUTHERN LOUISIANA. 75 



besides the first cost of the improvements to be considered in fixing the proper 

 relative capacities. 



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 usually 

 would be met if the plant were placed in the center of the district and dis- 

 charged 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 transporta- 

 tion of heavy machinery during the erection of the plant, as the ground usually 

 is much too soft to allow the hauling of heavy loads. Fuel also can then be 

 transported cheaply. If the tract has any considerable slope in its surface the 

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

 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 a plant can often 

 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. 



TTie foundation under both the machinery and the building of these plants 

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

 the plant at Gueydan has already been shown (fig. 16, p. 51) and is a good illus- 

 tration of a foundation in this character of soil. The foundation under the plant 

 on area No. 5, already illustrated (fig. 13, p. 45), is also a good one. It will be 

 noted on both these plans that the foundation is surrounded 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 pre- 

 cautions are necessary. The engine and pump usually are mounted on the 

 same block of concrete, so that any subsequent settlement will not throw them 

 out of line. While buildings to inclose the machinery should be of durable and 

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

 attendants from low winter temperatures. A frame of structural steel cov- 

 ered 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 already been discussed in detail in publications of this office. 1 While the 

 local conditions considered in these publications are somewhat different from 

 those in southern Louisiana, the same principles are involved, and the same 

 general features are to be considered. 



As stated previously, the average lift of drainage pumping plants is from 

 3 to 10 feet. The bulk of the water is lifted little more than 3 feet. Special at- 

 tention should therefore be given to the reduction of all friction and velocity 

 head losses to a minimum, as a poor arrangement of piping on the pumps may 

 easily double the total head against which they must work. The design of the 

 pump must be especially suited to such low and variable lifts in order to give 

 efficient service, the ordinary centrifugal pump for higher lifts being very in- 

 efficient under these local conditions. These pumps should also be so designed 

 that they are able to work under an overload. Increased capacity can then be 



1 U. S. Dept. Agr., Office of Expt. Stas. Bui. 243, Land Drainage by Means of Pumps, by 

 S. M. Woodward ; Circ. 101, The Selection and Installation of Machinery for Small 

 Pumping Plants, by W. B. Gregory. 



