18 BULLETIN 512, U. S. DEPARTMENT OF AGRICULTURE. 
ridge terraces can be obtained from the curves in figure 4 by adding 
one-half the vertical distance to the width of the bench for a 
horizontal-bench terrace. 
Were it not for the fact that the terraces would need to be placed 
very close together on steep slopes, thus necessitating a greater num- 
ber of terraces, it would be well to reduce the height of the terrace as 
the slope of the land increases. This would obviate the difficulty 
encountered in the construction of large terrace embankments on steep 
slopes. 
The equation from which the curves in figure 7 were constructed is 
based upon the assumption that the ends of the terraces are closed. 
In the field investigations many terraces with closed ends were found. 
Some followed contours completely around a knoll or hilltop, form- 
ing a closed circuit with no outlet. (See fig. 6.) But most of the 
level terraces examined had outlets at either one or both ends. In 
the foregoing discussion the terrace was taken as 1} feet high; with 
closed ends it would overflow for a rainfall in excess of 8 inches in 
48 hours. However, if one or both ends of a terrace be left open 
a liberal factor of safety against overflowing is provided. To pro- 
vide a factor of safety for terraces with closed ends it is recommended 
that they be made about 14 feet high. 
General discusston.—The success or failure of a broad-base level- 
ridge terrace depends largely upon whether or not it is laid out on an 
absolute level. Since the surface of the water stored above the terrace 
is level, it is imperative that all points along the top of the terrace be 
above this water level. If one point is low, the water flows over and 
soon washes away a section of the terrace. All of the water above the 
terrace then flows toward this crevasse and contributes to the further 
destruction of the terrace and often erodes a deep gully down through 
the field. Hence, in laying out a level terrace, the top should be main- 
tained at the same elevation throughout its length. 
It is desirable also that the base of the terrace follow the contour of 
the ground as closely as practicable. This often necessitates the use 
of very sharp curves and abrupt bends, but it eliminates the exist- 
ence of any low places or pockets above the terrace which collect and 
hold water on impervious soil. These sharp bends occur usually at 
crossings of draws and depressions. Most farmers object to them on 
account of inconvenience in cultivation and prefer to give the ter- 
race a gradual bend by crossing such places at a lower elevation. 
Then it is necessary to build the base of the terrace on lower ground 
and still maintain the top at the same elevation as that of the rest of 
the terrace, which requires that the terrace be built higher and wider 
at the base. (See fig. 8.) One landowner who was experienced along 
this line advised that a terrace crossing a gully or depression be built 
one-third higher than the required height of the terrace, to provide 
a a 
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