CHAPTER XVI 



OPEN DITCHES 



Drainage of Large Areas. Where large areas are to be 

 drained, it may not be practical to install tile of sufficient 

 size to care for the drainage water or run-off. Thus in the 

 large drainage systems it is to be expected that open ditches, 

 as distinguished from covered or tile lines, will be used to 

 supplement the tile. 



Construction of Open Ditches. In the construction of 

 open ditches, not only 

 the size must be con- 

 sidered, but also the 

 form of the ditch. 

 The size of the ditch 

 will depend upon the 

 capacity of ditches 

 dug to various grades 

 and upon the area 

 and character of the 

 catchment basin. The Fig. ce. 

 capacity of open ditch- 

 es will be discussed later. Care should be used in construct- 

 ing the banks of the ditch so that the ditch will remain 

 open and not become filled by the caving of the banks. 



In certain soils a slope of 1 foot horizontal to 1 foot ver- 

 tical for the sides of the ditch may be maintained; and in 

 other cases, as in the case of loam soil, the slope must be 1J^ 

 to 1, or even less. In digging a ditch it is often not possible 

 to secure the desired slope in the beginning, but the ditch 



103 



A floating dredge for digging open 

 ditches. 



