24 MISC. PUBLICATION 65 6, U. S. DEPT. OF AGRICULTURE 



to the terrace which is being used as a guide at that particular moment. 



3. Laying out the guide row : As the crew moves toward the terrace 

 outlet, the middle man, in locating the guide row will parallel first one 

 terrace and then the other. The middle man must be sure to keep the 

 same length of string between himself and the man in the terrace 

 which is being followed at that particular time. As the guide row is 

 established, stakes should be set at convenient intervals to mark its 

 location. 



When the area between the terraces is narrowing, the guide row 

 parallels the upper terrace. Therefore, the string between the middle 

 man and the man in the upper terrace is kept the same length, and the 

 lower man must take up the slack as it occurs in the string. When the 

 lower man feels the string begin to tighten, it indicates that the area 

 between the terraces is beginning to widen. From this point, the 

 guide row must parallel the lower terrace, so the string between the 

 middle man and the man in the lower terrace is kept the same length, 

 while the man in the upper terrace lets out string as required. When 

 the upper man feels the string begin to slacken, it means the area is 

 beginning to narrow again and that the guide row should begin to 

 parallel the upper terrace once more. 



When there is no change in the length of string, it indicates that 

 the terraces are parallel. Through a section of this sort the guide row 

 will have the same grade as the terrace. If this section is of consider- 

 able length some additional grade will be needed. Some type of level 

 will be helpful in obtaining an adequate grade. Twelve inches per 

 100 feet will give a 1-percent grade, which is generally considered to be 

 sufficient. In short intervals the additional grade can be estimated by 

 the middle man without danger of serious error. 



Remember these points : (a) The upper man never takes up string, he 

 gives it out in widening sections ; ( b ) the lower man never gives out 

 string, he takes it up in narrowing sections ; (c) the middle man holds 

 the same point on the string throughout the entire operation. 2 



Adapting the String Method to Different Terrace Patterns 



1. Where terraces drain in both directions : When terraces drain 

 both ways, the guide row is laid out first in one direction and then the 

 other from the starting point (fig. 16, A). In this case the guide 

 row starts from the highest point on the top terrace. 



2. Secondary guide rows: Where the first guide row empties in 

 the lower terrace, it becomes necessary to establish a secondary guide 

 row above the first (fig. 16, B). To do this, the middle man moves 



2 Two slightly different procedures in laying out the guide row have been found 

 satisfactory. Where only one man is familiar with the system, he may take 

 the middle position and determine by the string which terrace he is to follow. 

 He gives out string on the upper side when following the lower terrace. He takes 

 up string on the lower side when following the upper terrace. With this method 

 two strings have been found more handy, one for the upper side and one for the 

 lower, with surplus length on the upper side to allow for the widening sections. 



Where only two men are available, the wide and narrow points of the interval 

 are first located and marked. The man marking off the guide row parallels the 

 proper terrace by having man number two in the upper terrace when the interval 

 is closing. This man shifts to the lower terrace when the interval widens. 



