38 BULLETIX 652, U. S. DEPARTMENT OF AGBICULTUEE. 



In calculating the percentage of land that is in lateral ditches it was consid- 

 ered that for each ditch a strip of land 6 feet wide is lost to cultivation. 



The reservoir capacity, in inches of depth over the whole area, includes the 

 capacity of all canals between the general surface of land and the water level 

 5 feet below the surface. 



The pumping plant capacity was based on a velocity of 12 feet per second 

 through the discharge openings of the pumps. 



FACTORS AFFECTING DRAINAGE BY PUMPING IN SOUTHERN 



LOUISIANA. 



While the detailed descriptions of the four typical districts and the data 

 in Table I give a general idea of the drainage problems and the methods used 

 in solving them, it is believed that it will be of service to point out some of the 

 usual faults of plan and construction and to describe the best methods being 

 used in the design and construction of the drainage works. 



INVESTIGATIONS TO BE MADE BEFORE RECLAMATION. 



Before attempting to reclaim any body of wet prairie land, the following 

 points should be investigated thoroughly : 



( 1 ) The depth and character of the muck ; 



(2) The character of the underlying silt; 



(3) The elevation of the land above ordinary stages of the water in the 

 surrounding lake and bayous ; 



(4) The ordinary and extreme variation of the water level in these lakes 

 and bayous; 



(5) The elevation of the ordinary and maximum storm tides and the rate 

 of rise and fall ; 



(6) The amount and character of sunken timber and stumps; 



(7) The character of the timber or grass on the surface; and 



(8) Transportation facilities. 



In addition, the topographic features of each district should be investigated 

 in detail by a careful field survey, and a complete and definite plan and esti- 

 mate of cost worked out by a competent engineer. The work should be con- 

 structed under competent engineering supervision and should be of a permanent 

 nature, since the need for the improvements is permanent. 



AREA OF THE DISTRICT. 



Although topography has a large influence in many localities in fixing the 

 area of a reclamation district, there are many large bodies of land of such a 

 character that the size of the unit would be determined almost entirely inde- 

 pendently of topographic conditions. In order to make clear the conditions 

 governing the determination of the most desirable size of unit, the respective 

 advantages of the .small and large districts will be enumerated. The prin- 

 cipal advantages of the small unit are : 



(1) Short internal drainage canals with small losses of head, and the con- 

 sequent low lift ; 



(2) Short haul to outside water transportation; 



(3) Small area affected in case of failure of protection levee; 



(4) Small capital involved; and 



(5) Short time required to place land under cultivation and early realiza- 

 tion on investment. 



