WET LANDS OF SOUTHERN LOUISIANA. 



53 



canals at the end of the first 24 hours. At the end of the second 24 hours the 

 surplus still would be 0.4 inch, while at the end of the third day it would have 

 been reduced to 0.2 inch. Before the end of the fourth day the pumping plant 

 would have lowered the water to a level 5 feet below the surface of the land. 

 Since the greatest amount of surplus water left in the reservoir at any time was 

 0.4 inch, a reservoir having this capacity would be able to prevent flooding, 

 provided the run-off was as shown on the Smithport curves. By making oihcr 

 assumptions as to capacity of plant, the corresponding capacity of reservoir 

 can be approximated. Then by calculating the cost of each pumping plant and 

 each reservoir, using current prices for material and earthwork, the cheapest 

 combination can be determined. 





§2 



COMPOSITE OF EIGHT DISTRICTS 



FOR WHICH SEPARATE CURVES ARE SHOWN 





















J*W S 





















A 



0°J^" 





















3 



M> 





















2 



d*£> 











































l 



<M*~< 



















































? 





1 



* 



1 







( 



> 



7 



Rain fa// in inches 



Fig. 15. — Probable actual run-off from drainage districts in southern Louisiana. 



In general, a system of reservoir canals having the proper depth and width 

 to give good drainage to the entire area, and allowing the use of average-sized 

 dredges to construct them, will have a reservoir capacity of about 0.5 inch in 

 depth over the entire tract. This size will be ample to bring the water to the 

 pumping plant fast enough to secure continuous operation until the water is 

 lowered sufficiently in the portion of the canals most remote from the plant. 

 While a further increase in the size of the reservoir will allow a certain re- 

 duction in the capacity of the pumping plant, the combined cost will usually be 

 greater with this increase of reservoir. In other words, after a certain point is 

 reached it is cheaper to increase the capacity of the pumping plant than it is 

 to incease the capacity of the reservoir canals. 



