32 BULLETIN 512, U. S. DEPARTMENT OF AGRICULTURE. 
level-ridge terrace possesses a decided advantage over the horizontal 
bench terrace with respect to the elimination of weeds and waste 
land, and over the graded terrace with reference to the movement of 
the surface water. 
In view of the above discussion it is recommended that the broad- 
base level-ridge terrace be used wherever conditions of soil and 
topography will permit—that is, where the soil absorbs a portion 
of the rainfall and the slopes are not too steep. The broad-base level- 
ridge terrace supplemented by efficient tile drains suitably located 
would afford the most ideal method for preventing soil erosion on 
any type of soil. Often the yields obtained and the saving resulting 
from the absence of soil erosion would justify, in a financial way, the 
installation of tile. 
LAYING OFF A TERRACE SYSTEM. 
The courses to be followed by the terrace lines are governed by the 
topography of the field. This is well illustrated in figures 14 to 16. 
Where the slope of a field is practically uniform and in one direction 
(fig. 14) the terrace lines will be straighter and more regular than 
where the slopes vary much in amount and direction (figs. 15 and 
16). Figures 14 and 15 show fields having broad-base level-ridge 
terraces. It will be noted that the terraces follow approximately the 
contours of the ground. Figure 16 illustrates a field of broad-base 
graded-ridge terraces. In this case the terraces are seen to cross the 
contours. 
It must be remembered that a terrace is designed to provide for 
the run-off water from a limited area above it and when this area 
is exceeded the stability of the terrace is endangered. A very com- 
mon cause of failure of terrace systems is the fact that the upper ter- 
race in the field is made to drain an excessive area. As a result, the 
upper terrace breaks, and a large volume of water rushes down the 
slope, breaking all terraces below. Frequently a farmer desires to 
terrace his farm but his neighbor’s farm lies at a higher elevation and 
the upper terrace would be required to handle run-off water from 
his neighbor’s land. In such cases an attempt should be made to in- 
duce the neighbor to terrace his farm also. If this can not be done 
the water from above must be intercepted by means of a hillside 
ditch to carry the water to the nearest drainage channel below. 
The success or failure of a terrace system is largely a matter of 
proper laying off of terrace lines. Various kinds of homemade 
devices are employed for laying off terraces, but unless the operator 
exercises special care in the use of them the results usually are poor. 
Many landowners realize the inefficiency of these devices and have 
adopted as a substitute a cheap form of telescopic spirit level 
mounted on a tripod. Even with this level, in the hands of an 
