i6o 



FARM DEVELOPMENT 



ing the corners of farms and recorded in a drawing or 

 drainage map. By placing the distances and angles on 

 this map, any underdrain can be located at any point 

 at any future time, by again measuring from the given 

 points and base lines. (See Transit in Figure 58.) 



Leveling instruments are even more generally useful 

 and necessary, in planning and constructing drains, than 

 the transit. Very often they are necessary to aid in 

 getting the general level of the land so as to determine 



where to locate the 

 - drains so as best to 

 reach wet areas and 

 carry off the water in 

 the most effective man- 

 ner with the minimum 

 cost of construction. 

 For example, in the 

 Valley of the Red River 

 of the North a drainage 

 engineer was employed 

 to lay out a general plan 

 of drainage. The land 

 level placed on tripod and was so nearly level in an 

 area 40 by 100 miles that, 

 with his assisting engineers, he surveyed east from the 

 Red River of the North through this district, taking 

 the level at every section corner and also at half mile 

 posts along all east and west section lines. When all 

 this had been done, the figures representing the height 

 of each point above datum plane* were recorded on a 

 map of the entire territory. By examining these figures, 

 the engineer was able to map out all the low areas 

 through which large drainage canals were needed to 



*A datum plane is an imaginary level plane used as a basis for 

 comparing the heights of points at or near the surface of the ground. 

 It is usually assumed 100 or 1,000 feet below some stated point or 

 sea level. 



Figure 

 supplied with sights. 



