68 



AGRICULTURAL ENGINEERING 



placing a tile deep, a large reservoir is provided for rainfall, 

 and the tile will have a longer time to carry the surplus away. 

 Distances between Drains. It is a practice in some 

 localities where an average soil exists, to consider that tile 

 will drain the water from the soil to a distance of one rod for 

 each foot in depth. As the ground water flows away through 

 the. tile lines after heavy rains, the level of the ground water 

 is first lowered directly over and near the tile, which causes 

 side flow of the water through the soil. If the soil is open or 

 sandy, this flow through the soil is rapid, and the level of the 



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Fig. 44. Sketch showing how the ground water is lowered and the capacity 

 of the soil as a reservoir increased by placing the tile deep. 



ground water between the tile lines will be lowered quickly, 

 and at no time will it be much higher than the level near the 

 tile lines. 



If the soil be retentive and resistant to the flow of the 

 water to the tile lines, the ground water may come very near 

 the surface at a rod or two from the tile. Thus the distance 

 between the lines depends not only upon the depth of the tile, 

 but also upon the character of the soil. In practice, lines 

 are placed 50, 75, 100, 150, and 200 feet apart, for average 



