DRAINAGE 



107 



Number of acres drained by open ditches. 



Depth of water 7 feet. Depth of ditch at least 9 feet. 



Grade 



Average width of water 



Per 

 cent 



Feet 

 per mile 



8 

 feet 



10 

 feet 



15 

 feet 



20 

 feet 



so 



feet 



50 

 feet 



0.02 



0.04 

 0.06 

 0.08 

 0.10 



0.15 



0.20 

 0.25 

 0.30 

 0.40 

 0.50 



1.0 

 2.1 

 3.2 

 4.2 

 5.3 



7.8 



10.6 

 13.2 

 15.8 

 21.1 

 26.4 



2300 



4850 

 5920 

 6940 

 7720 



19400 



22400 

 25000 

 27400 

 31700 

 35400 



4700 

 6740 

 17000 

 19100 

 21800 

 27000 



31300 

 34800 

 38200 

 44100 



16600 

 23400 

 29600 

 34200 

 38400 

 47200 



54200 

 60500 

 66200 



28000 

 35400 

 43400 

 50000 

 56000 

 68500 



78700 

 88000 

 96500 



48000 

 58000 

 72000 

 83000 

 92600 

 112000 



130000 

 146000 



88500 

 106000 

 129000 

 150000 

 167000 

 202000 



235000 



QUESTIONS 



1. When may it be necessary to use open ditches as drains? 



2. What are some of the disadvantages of open ditches or drains? 



3. What slope is usually given the sides of open ditches? 



4. What is the "waste bank"? The "berm"? 



5. How much does the digging of open ditches cost per cubic yard? 



6. What factors influence the capacity of open ditches? 



7. What formula is generally used in computing the capacity of 

 open ditches? 



