DRAINAGE 273 



necessary to drain all of them and for finding the most 

 practical outlet through the ridges. 



Outlet channel. The outlet channel should be examined 

 for the purpose of determining the height to which the water 

 will rise in a flood period, the season of the year in which 

 the flood occurs, and the length of time the outlet remains 

 at flood height. A stream that floods when the frost is 

 going out of the ground in the spring or once every eight or 

 ten years might afford a satisfactory outlet for a drainage 

 system, but if it floods between May and August two or 

 three times a season, and remains at high- water stage for 

 two or three days at each flood, it would be inefficient and 

 crops would be drowned and the drainage system be ren- 

 dered almost worthless. 



Crops. Crops to be raised have an influence upon drain- 

 age plans, since some crops are much deeper-rooted than 

 others and require drainage to a greater depth. To a cer- 

 tain extent the growing season determines the drainage 

 required. Flood periods that might not injure one crop 

 would completely ruin another. 



Soil. The nature of the soil must also be taken into 

 consideration. This will become evident in the work of 

 excavating, as it takes much less labor and time to dig a 

 satisfactory ditch or tile trench in one kind of soil than in 

 another. 



Cost. The cost of material and labor affect a drainage 

 plan only in the first cost, but this estimate of the cost of 

 the work may determine its construction. A proper con- 

 sideration of this point will prevent delay in the work 

 because the estimate is too high or future dissatisfaction 

 because the estimate has been too low. 



Run-off. Run-off is the water which is carried from the 

 land either by the natural channels or by the construction of 

 new channels. The quantity of run-off is dependent upon 

 the slope, the condition of the soil, and the vegetable growth. 

 A hard, firm surface prevents the rainfall from entering the 



