Attack by Drainage 141 



When natural watercourses are treated in this 

 way advantageous realignment is first made; and 

 grades are used that fit the topography; in many 

 cases causing the actual length of the stream to be 

 considerably shortened, and its velocity increased. 



Whenever ditches are lined, sufficient weep holes 



Junction of Branch Ditch 

 and Main Ditch 



Branch ditches shotild join main ditches at an 

 acute angle or on a curve. 



must be installed to enable the water that follows 

 the sides of the concrete lining to enter the ditch. 

 When weep holes are omitted water is apt to stay 

 in puddles near the stone lining. Water has a 

 tendency to flow along the side walls and under 

 lined ditches. In many instances this is sufficient 

 to tear away the earth supporting the ditch sides 

 and at times even to undermine the lining. This 

 action is prevented by installing key walls at right 



