34 



BULLETIN 512^ U. S. DEPARTMENT OF AGRICULTUEE. 



a hoe who digs a hole at each position of the rod to serve as guides 

 to the plowman who follows immediately and lays out the first 

 furrow. This is the cheapest and most satisfactory method of laying 

 out level terraces. 



Several terraces may be laid out from one position of the instru- 

 ment, depending upon the vertical interval and length of the rod. 

 If the entire length of the terrace can not be seen from one position 

 of the level, the rodman should retain the rod at the last point visible, 

 the instrument should be moved to a new position, and a reading of 

 the rod taken. This reading should be used in locating points on the 

 terrace line from the new position of the instrument. 



too- — . 

 iiiiiiHiiiiiHiim 



Fig. 15. — System of level-ridge terraces on a field having irregular slopes. 



The graded terrace is more difficult to lay out than is the level 

 terrace, because the rod readings never are the same for any two 

 points on the terrace line. The first point on the terrace line is 

 found in a manner similar to that described for the level terrace. 

 Assuming that the terrace drains to one outlet, then a fall will occur 

 from the middle of the terrace line toward the outlet and a rise in the 

 other direction. If, for instance, a grade of 0.4 foot per hundred 

 feet be used, and if guide stakes are to be set 50 feet apart where the 

 alignment is fairly straight and 25 feet apart on bends, then for each 

 25 feet in distance toward the outlet a fall of 0.1 foot would be 

 required, and, therefore, for each 25 feet in the direction of the 

 outlet the rod reading should be increased 0.1 foot. The distance 

 should be measured with a tape. If a variable grade is used the rod 

 readings should be computed accordingly. 



