WET LANDS OF SOUTHERN LOUISIANA. 55 



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

 general features are to be considered. 



The average lift of tin 4 drainage pumping plants is from 4 to 6 feet, with the 

 total head ranging from to 10 feet. Special attention should be given to the 

 reduction to a minimum of all friction and velocity-head losses, as a poor ar- 

 rangement of piping to the pumps may easily increase the total head 50 to 

 75 per cent. Plants have been inspected where the total head on pump was 

 nearly double the useful lift. The cost of properly designed pipes is very 

 little more than that of pipes which cause large losses. 



The design of the pumps must be especially suited to low and variable lifts 

 in order to give efficient service. The ordinary centrifugal pump designed 

 for higher lifts is very inefficient when used on low-lift conditions. Sometimes 

 it is advisable to design the pumps to run most efficiently at considerably less 

 than the maximum capacity required of them when the demand is the heaviest. 

 Thus nearly all the water can be pumped while running the pumps at the best 

 possible capacity for efficiency, as the number of days per year that the plant 

 will be called upon to operate at its maximum capacity are very few, averag- 

 ing perhaps five. In this way a comparatively small and cheap plant can be 

 installed and the maximum required capacity obtained by speeding up the 

 pumps above their normal rate. 



Various types of pumps have been examined in the plants inspected. The 

 horizontal centrifugal pump and the horizontal screw pump are the only ones 

 entirely suitable for drainage service of this nature. One large rotary pump 

 was inspected, and while it was pumping water very efficiently, the minimum lift 

 through which it could work was 10 feet, which was nearly twice the required 

 lift. Such pumps are more expensive and require more expensive foundations 

 than do centrifugal pumps. 



It is advisable to install not less than two units in a plant. The low stages of 

 water in the reservoir canals can then be handled properly, and a breakage of 

 machinery would not render the plant inoperative. Owing to the fact that the 

 soil on the average reclamation district will subside from 2 to 3 feet during 

 the early years of reclamation, both the average and the maximum lift of the 

 pumping plant will probably increase by that amount. Provision should be 

 made for this increase of lift by having sufficient power for driving the pumps 

 and by having the suction pipe of sufficient length. 



On all pumps some means should be installed of indicating whether or not 

 they are discharging at the proper rate under a given set of conditions. Vegeta- 

 tion growing in the reservoir canals will be carried through even a closely 

 spaced screen in the suction basin and will lodge on the impellers ; this will 

 reduce the capacity materially even if its presence can not be detected by the 

 most careful operator. Tests have been made on plants where the capacity was 

 reduced as much as 30 per cent from this cause. Where the pump has two 

 suction pipes, vacuum gages installed on the pipes close to the pump will indi- 

 cate by a sudden change in pressure that debris has" become entangled in the 

 impeller. An instrument known as a rate-of-flow meter, reading in thousands 

 of gallons per minute, has been devised for connecting to the discharge pipes; 

 this will indicate at all times the amount of water passing through the pumps. 

 If the amount of water indicated by this meter is less than it should be for a 

 certain lift and speed of rotation of the impeller, the pump should be cleared 

 of debris at once. After pumps are installed a thorough test should be made 

 to see whether or not they come up to the guaranteed efficiency and to determine 

 the proper speed at which to run them to obtain the best efficiency. 



All the older pumping plants in this section were driven by steam engines ; the 

 types of engine varied from the cheapest slide-valve to the most expensive type 



