AGRICULTURAL ENOINEERING 267 



Siirface drainage is provided by digging ditches through 

 and from a field needing drainage to a lower place called 

 the outlet, as a ravine, a river, or a lake. Unless land is 

 higher than the lake or river to be used for an outlet, it 

 cannot be drained in the usual way. A ditch, to be effective 

 in draining land, must start at the lowest place to be drained 

 and continue in a downward slope to the outlet. Drain- 

 age water can run of its own accord only down hill. Sur- 

 face drainage is the cheaper method and the more common. 

 The chief objection to it is the continual work necessary 

 to keep the ditches open. Grass and weeds grow in them 

 and clog them up and earth washes into them or is worked 

 into them by cultivation. Open ditches are also trouble- 

 some to work around. The space occupied by the ditch 

 is wasted, and weeds are likely to make it unsightly. 



Tile drainage is the more expensive form of drainage, 

 but is very much to be preferred. Tile are pipes three or 

 more inches in diameter, one foot long, and are made either 

 of clay or concrete. Clay tile are at present more common 

 than concrete. Tile are laid in the ground two and a half 

 feet or more deep, and on a gradual grade or slope, so that 

 any water that gets into them easily runs down the tile to 

 the outlet. Good tile drainage work requires the use of 

 rather accurate leveling instruments, and careful work in 

 lajdng the tile to insure a continuous slope, so the water will 

 all run out. Good tile, well laid, will last almost indefinitely. 

 They are covered with soil, so that there are no irregular 

 fields, waste land, or unsightly strips of weeds, as is the case 

 with open ditches. 

 Questions: 



1. What do you imderstand by the term drainage? 



2. What are the advantages and disadvantages of open or sur- 

 face drains? Of a tile drain? 



Arithmetic: 



1. If drain tile are 1 ft. long, how many rods of drain will 100 

 tile lay? 



2. If tile cost $30 per 1,000, how much does enough tile to lay 

 one rod cost? 



3. If an acre of drained land yields 50 bus. of com per year 

 worth 50c. per bushel, and it costs $15 per acre to grow the crop, 

 how much profit will there be per acre? How many similar crops 

 will it take to pay for its drainage, if it cost $25? 



