PREVENTION OF EROSION BY TERRACING. 33 
inexperienced or careless operator, the results obtained are far from 
satisfactory. Surveys of seven level-terraced fields where a level of 
the above type was used showed an average variation in level along 
the terraces for each field ranging from 0.4 to 2.6 feet. The engi- 
neer’s Y level is by far the most satisfactory instrument for this 
work and the results obtained warrant the small expense of employ- 
ing a competent engineer or surveyor who has such an instrument. 
A number of surveys of 
terraced fields laid off with 
an engineer’s level in the 
hands of experienced level- 
men showed remarkably lit- 
tle variation from the level 
or uniform grade line. 
Laying off level-terrace 
lines is a simple leveling 
proposition which consists 
merely of following con- 
tours of the field with a 
chosen vertical interval be- 
tween them. The terrace 
nearest the top of the field 
should be laid off first. The 
level instrument should be 
set in a position near the 
middle of the terrace line SO) goppoyrs 
as to command a view of the /erraces....- 
ae 
~S 
ao. 
SA G I YC FONE Ce DCG 
OMe we SO 
See? 
tr edhavy 
a ie 
whole length of the terrace, Sewn Guees 
and sufficiently high so that ia OA epee ay UREN ste 
the bottom of the rod. when Fic. 14.—System of level-ridge terraces on a field 
2 having regular slopes. 
set at the highest point in 
the field, is slightly below the level line of sight of the instrument. 
If, for instance, the reading observed on the rod at the highest point 
be 0.5 foot and the vertical distance between terraces is to be 3 feet, 
the rod is placed at a point directly down the slope where the rod 
reading is 3.5 feet. To establish the line of the terrace, points of 
equal elevation should then be located to both ends of the terrace at 
intervals of 25 to 50 feet, the closer spacing being used for land of 
irregular topography. Invariably a point should be established 
where the terrace line crosses a draw, gully, or depression. ‘The 
points established may be marked permanently by stakes to be used 
subsequently as guides in the construction of the terrace. A very 
common method is to lay out and construct the terrace at the same 
time, or at least to plow one furrow to establish definitely the line 
of the terrace. In this method the rodman is followed by a man with 
