DRAINAGE 2O5 



these blocks, just as the device shown in Figure 96 is 

 adjusted to similar changes in grade by moving the bolt 

 supporting the upper board into holes one-third of an 

 inch lower. If the device is shorter than i6 l / 2 feet, the 

 size of the blocks used in placing the nails should be 

 proportionately thinner. Thus, if 10 feet long, the 

 blocks should be one-fifth of an inch thick. Figure 96 

 illustrates a grading frame used in leveling ditches. 

 A, spirit level; B, hinged end of board at back or lower 

 end of frame ; C, loose end of board at front of frame, 

 which can be lowered or raised, so that, when the spirit 

 level stands level, the bottom board, D to E, will have the 

 desired slant to give the 

 bottom of the ditch the 

 proper grade. The frame 

 is pulled forward as fast 

 as the ditch is lowered 

 sufficiently to allow of 

 its being moved without 

 throwing the spirit bulb ~ Figure 95> ^^^^ drain grader . 

 out of level. A change 



for a steeper grade is made by putting the pin at C 

 in a lower hole, and to a slighter grade by putting 

 the pin in a higher hole. 



Grading devices. In Figures 95, 96, 97 and 98 are 

 shown different forms of leveling devices found useful 

 in making the bottom of the tile drain at a uniform 

 grade. Proceeding from one station to another, the 

 accuracy of the grading frame is tested by measuring 

 down from the stake at the new station. If the grade 

 has been too great, and the ditch is not sufficiently deep, 

 the grading frame should be readjusted to a slightly less 

 grade, and if the ditch is too deep when the forward 

 station is reached, the frame should be readjusted to 

 a greater slant. 



A small steel wire, such as is used in wrapping brooms, 



