106 



AGRICULTURAL ENGINEERING 



Bulletin 78 of the Iowa experiment station. A coefficient of 

 roughness of .03 has been used and they are for ditches having 

 the sides with slopes of one foot horizontal to one foot vertical . 

 The ditches are not to run more than 8-10 full, where the 

 capacity is mentioned. Above the upper heavy lines in 

 the table the % inch standard of water for 24 hours is used ; 

 between heavy lines the Yi inch standard; and below the 

 lower heavy lines the \i inch standard. 



Number of acres drained by open ditches. 

 Depth of water 5 feet. Depth of ditch at least 6J^ feet. 



Grades 



Average width of water 



Per 



cent 



Ft. 

 per 

 mile 



6 

 feet 



8 

 feet 



10 

 feet 



15 

 feet 



20 

 feet 



80 

 feet 



50 

 feet 



0.02 



1.0 



980 



1470 



1900 



5000 



7150 



23800 



43800 



0.04 



2.1 



1390 



2090 



2800 



7200 



20400 



33500 



62500 



0.06 

 0.08 



3.2 



4.2 



1710 

 1980 



2560 

 2980 



5100 

 6100 



17600 

 20400 



24700 

 30000 



40800 



48800 



75500 

 88000 



0.10 



5.3 



2220 



5010 



7600 



23400 



83400 



54500 



98000 



0.15 



7.8 



2720 



6300 



17100 



28700 



40500 



66700 



120000 



0.20 



10.6 



4820 



7300 



19500 



33000 



47000 



77000 



139000 



0.25 

 0.30 

 0.40 



13.2 

 15.8 

 21.1 



5370 

 5900 

 6830 



16300 

 17900 

 20600 



21900 

 23900 

 27700 



37500 

 40700 

 47000 



53000 

 57000 

 67000 



86000 

 94000 



155000 

 170000 



0.50 



26.4 



7600 



23000 



31000 











0.60 

 0.70 

 0.80 

 0.90 



31.7 

 37.0 

 42.2 

 47.5 



16700 

 18100 

 19000 

 20500 



25200 

 27300 



33900 











