LAND DRAINAGE PRACTICE. 



39 



** The lines of tile in the field were laid 33 feet apart 

 and about four feet below the surface. Small wells 

 were sunk midway between the lines of tile and were 

 therefore 16^ feet distant from drains on either side. 

 The soil of the field consists of 6 or 8 inches of medium 

 clay loam, followed by 2-| to 3 feet of clay, below which 

 is a stratum of rather coarse sand, in the upper surface 

 of which the tiles are usually laid. The tiles are three 

 inches inside diameter, and are laid on a grade of about 

 two inches in 100 feet. At the time the levels were 

 taken the tiles were discharging only one twentieth of 

 their capacity. 



'^ The observed contour of ground-water in this field 

 at 8 A. M., May 13, forty-eight hours after a rainfall of 

 .Sy inch, is represented in Fig. 3. The highest water 

 level in any well between these lines of tile on this date 

 was one foot, in the case of well A measured above the 



0lHiJfM7//M 



Fig. 3. — Line of Saturation between Tile Drains 48 hours after a Rain- 

 fall of -^Q of an inch. 



level of drain No. 14. The least was about .3 foot, in 

 the case of well E above tile No. 18. Both wells C 

 and E were sunk into a sand containing a considerable 

 amount of gravel, and to this fact is probably due the 

 less steep gradient at these places. Between well B 

 and tile 16 two other wells were sunk, one two feet 

 from the drain, and the other midway between the 



