DRAINAGE 85 



2. What size tile should be used to drain properly a 40-acre tract, 

 if the line is 1200 feet long and laid with a grade of 3-10 of a foot per 

 100 feet? 



(The following problems are taken from Bulletin 78 of the Iowa 

 experiment station, involving the use of the table.) 



3. What size of tile laid to a 0.1 per cent grade will carry the under- 

 drainage of 160 acres of flat land? Ans., 15 inches. 



4. What size of tile laid to a 0.2 per cent grade will carry the under- 

 drainage of 240 acres, % rolling? Ans., 80 acres flat land plus % of 

 160 acres rolling gives 133^ acres, requiring a 12-inch tile. 



5. What size of tile laid to 0.3 per cent grade will be required to 

 remove both ground and surface water from a pond whose watershed 

 includes 40 acres? Ans., 10-in. (Note. Double or triple the area for 

 both ground and surface water.) 



QUESTIONS 



1. What causes the flow of water in tile drains? 



2. What are some of the factors which influence the velocity of the 

 flow of water in tile drains? 



3. Give and explain Poncelet's formula. 



4. What modifications of the formula may be made, and why? 



5. What is meant by a standard drainage coefficient, or standard? 



6. How is Poncelet's formula used? 



7. How may the capacity or discharge of a tile be obtained from 

 the velocity of flow? 



8. Why is a table convenient in determining the size of tile? 



9. What is meant by maximum length of tile lines? 



