32 BULLETIN 512, U. S. DEPARTMENT OP AGEICULTXJEE. 



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 



