56 BULLETIN 304, U. S. DEPARTMENT OF AGRICULTURE. 



by profiting by the experience of the districts already under drainage, 

 the new districts will undoubtedly save much money and secure more 

 satisfactory drainage improvements. The best way for one unfa- 

 miliar with this kind of drainage to become informed on the subject 

 is to visit and inspect thoroughly a number of the completed districts. 

 Tables 20 and 21 give lists of such districts, with information as to 

 location, size, etc. 



SUMMARY. 



Numerous tracts in units of from 5,000 to 20,000 acres have been 

 reclaimed along the Illinois River and on both sides of the Mississippi 

 in the States of Illinois, Iowa, and Missouri. In the average district 

 the cost of the general drainage improvements, including levees, 

 ditches, and pumping plant, has been about $30 per acre. This 

 method of reclamation may be expected to be extended constantly 

 to new localities as agricultural land becomes more valuable. 



The design and construction of the levees, ditches, and pumping 

 plant require a considerable degree of engineering ability. Poor de- 

 sign may result either in a system so inadequate for its purposes as 

 to render the benefit to the land insufficient to make the undertaking 

 profitable, or it may lead to an expenditure for construction greatly 

 in excess of the amount that could have been made to suffice. In 

 general, the inexperienced tend to underestimate greally the extent 

 and expense of the work required in such reclamation. 



The levees must originally be made of such height and thickness 

 as to afford ample strength and they must also be given careful sub- 

 sequent attention to secure proper maintenance. The internal drain- 

 age ditches should be deep enough to keep the ground-water level at 

 least 3 feet below the surface and their capacity should be sufficient 

 to discharge heavy rains freely to the pumping station. Streams 

 entering the district from higher ground should be diverted around 

 the levees where such a plan is feasible, and provision should be made 

 in such diversion ditches for the collection and storage of silt from 

 hill streams. 



The pumping plant should have a capacity sufficient to remove as 

 a minimum amount in 24 hours a quantity of water sufficient to 

 cover the entire district to a depth of 0.3 inch. The capacity should 

 be greater in situations of heavy rainfall and where the run-off of 

 rolling land is received in the district. 



The pumping machinery should be so arranged as to reduce to a 

 minimum the work of disposing of the surplus water, and it should 

 be chosen with especial regard to economy and efficiency in opera- 

 tion. Where large fluctuations in the river level are to be expected 

 the machinery must be sufficiently large to operate at the maximum 



