104 AGRICULTURAL ENGINEERING 



is made deep enough so that as it caves in it will still be of 

 sufficient size. The heap of excavated earth from a ditch is 

 called the waste bank. The space between the waste bank 

 and the edge of the ditch is called the berm. Waste banks 

 present an ugly appearance and are an objectionable feature 

 of open ditches, unless the earth is used to fill in low places. 



Cost of Open Ditches. Small open ditches are made 

 with the plow or scraper. These are usually undesirable, as 

 they do not furnish a good outlet for the ground water. 

 Large open ditches are generally built by contractors who 

 are provided with ditching or dredging machines. In many 

 cases these are floating dredges which begin at the head of the 

 ditch and dig toward the outlet. There are other types of 

 ditching machines, which operate on tracks laid on each side 

 of the proposed ditch. These large machines remove the 

 earth from the ditch at a very reasonable cost, varying from 

 5 to 15 cents per cubic yard. 



Disadvantages of Open Ditches. There are many dis- 

 advantages of open ditches. Small ditches do not furnish 

 good outlets for the ground water because they cannot be 

 kept open to sufficient depth. It is to be noted that an open 

 ditch will not drain below the surface of the water in the 

 ditch. Again, open ditches interfere seriously with the culti- 

 vation of the land, and are very unsightly. They occupy 

 so much land as to make their upkeep expensive. Further- 

 more, more plant food is carried off by an open ditch than by 

 a tile drain. If the water must pass down through the soil 

 to a tile drain, more or less of the plant food will be left in 

 the soil. 



Capacity of the Open Ditch. As in the case of tile drains, 

 there have been many attempts to prepare a formula which 

 would enable one to compute the capacity of open ditches. 

 There are a good many factors which influence the flow of 



