DRAINAGE 



175 



cases it will be necessary to traverse the land with map 

 in hand, and by inspecting both the map and the land, 

 the drains may be placed in the most practicable posi- 

 tions. In some cases it will be necessary to accompany 

 the general inspection of the map and land, with meas- 



/ / 

 / 



Figure 79. The curved contour lines, drawn through points of similar 

 show the height of each part of the land above the outlet of the drain A. 

 of the land is at right angles to the contour line. 



elevation. 

 The slope 



urements of the heights of points along the trial line? 

 made by leveling instruments, and, where the expense is 

 considerable, it will be wise to make profiles showing the 

 amount of digging required in case of each of two or 

 more ditches projected in the preliminary surveys. 

 Since the whole system of drainage must be taken into 



