OPEN DRAINS. I77 



as shown in Fig. 32. Provision should be made at all 

 points where water discharges into open ditches in 

 large quantities to cut off the overfall. Much injury 

 to ditches and after expense in cleaning out may in 

 this way be avoided. The line AB in the figure shows 

 how the grade of a shallow ditch which discharges into 

 a deeper one should be changed in order to avoid the 



i^h}\^)ryilii.yl!if'S.' 2m}}}ff 



Jk . 



fiia.de df '^laneh 



df 'Bla nch 

 _ B 



mimiijui'i ^'"' 

 Fig. 32. — Section showing Junction of Shallow Bitch with Deep Main. 



erosion of earth and consequent filling of the receiving 

 ditch which will result if the side ditch is permitted to 

 discharge on its regular grade by an overfall. 



Special Forms for Ditches. 



In practice, ditches are not made in the same form, 

 but are adapted to the material through which they are 

 made, the means used for their excavation, and the 

 office they are to perform. 



The cuts in Fig. 33 show forms of ditches which may 

 be found in use and serve their purposes well. Fig. A 

 is the common form left by the floating dredge in level 

 districts where the depth is from 6 to 8 feet. 5 is a 

 form used lor a deeper ditch where clay through which 

 it is cut is sufficiently firm to stand. T is a form used to 

 provide for flood water from hills. For ordinary drain- 

 age the smaller channel is sufficient. This is adapted 

 to a ditch with light grade, but which receives water 

 from adjoining territory which has a heavy grade and 



