DRAINAGE. 23 



4. Amount of water -brought in by springs and adjacent territory. 



5. The nature of the crops to be produced. 



6. The depth of the ditch. 



The deeper the drain, the wider the area that will be 

 drained. In open soils drains should be deeper and farther 

 apart than in close stiff soils. 



Tile are put in from 2 to 4 feet deep according to the varia- 

 tions in the character of the soil. 



Successful alfalfa growing depends upon deep tiling. 



The deeper the drains the more water will be carried, when 

 the drains are close enough to each other to keep the water table 

 at about a uniform depth. 



If a soil has had its non-capillary pores emptied to a depth 

 of 3 feet, and another soil has had its pores emptied to a depth 

 of 2 feet, the capacity of the deeper drain for storing a heavy 

 rainfall is far greater than that of the shallow drain. 



How the Water Enters the Tile. 



When glazed tile are used, water can only enter by way of 

 the joints, but where porous tile are used water enters the drain 

 both by way of the joints and through the walls. 



Experiments have demonstrated that water will pass 

 through the walls of cement tile much more rapidly than 

 through clay tile. 



When water flows through tile for a considerable distance 

 the friction of the water against the walls of the tile, greatly 

 retards the flow of water. 



When the flow of water is retarded by friction, joints, and 

 curves, provision for greater flow must be made by using larger 

 tile. 



* On account of the friction on the walls of small tile, the 

 amount of water carried when tile are running full, will increase 

 faster than the squares of their inside diameters as the tile are 

 increased in size. 



* The area of the opening in an 8 inch tile is four times as great 

 as that of a 4 inch tile, but the friction in the 4 inch tile is greater in 

 proportion to the amount of water carried than in the 8 in. tile. 



