32 



IOWA DEPARTMENT OF AGRICULTURE. 



face of the road in rolling countries, provided they have a fall of not 

 less than three-tenths of a foot to each 100 feet. Outlets into side ditches, 

 or preferably into the adjacent fields or streams, should be provided as 



Fig. 11.— Longitudinal section at "xy," on figure 7, showing discharge of subdrain into 



culvert pipe. 



often as practicable. The size of the drains will depend upon the dis- 

 tance between outlets as well as the grade of the ditch. Ordinarily if 

 the distance is 500 feet or less, 3-inch pipe will answer. If the distance 

 is greater than that, the size of the tile should be increased about 1 inch 

 in diameter for every 400 feet in length. 



In the prairie states, where the roads are practically level, it is 

 sometimes advisable, to construct blind ditches of vitrified clay tiles, 

 into which the contents of the subdrains above mentioned can be dis- 

 charged. (Fig. 12.) Water can be carried a long distance in well-laid 



Fig. 12. — Cross section of underdrained level road, showing method of discharging 

 subdrains into a larger and lower pipe. 



pipes with but little fall. Six or 8-inch pipes can be placed alongside 

 the road, with a fall of 1 inch to the 100 feet, if carefully laid, with the 

 discharge in a river or stream. Such drains can be run several miles 

 with the fall mentioned, and their size increased, if necessary, as they 

 approach the place of discharge. The level road can then be drained 

 by giving the subdrains a fall of about 3 inches to each 100 ieet. The 

 upper end of these drains can be from 12 to 18 inches below the surface, 

 and the lower end, where the discharge is made into the large pipe, 

 can be 3 or 4 feet below the surface. The operation can then be repeated 

 until the entire surface is underdrained. (Fig. 13.) 



Fig. 13.— Longitudinal section of underdrained level road, illustrating a system whereby 

 fall can be secured for subdrains. 



LAYING OF SUBDRAINS.— The greatest care should be exercised 

 in the laying of subdrains. They should be carefully graded and should 

 have a continuous and even fall throughout their entire length. But it 

 requires no special engineering skill or expensive instruments to lay 



