494 STATE BOARD OP AGRICULTURE. 



greater depth is preferred. This drain would be only 27 inches deep at 

 stake 3. 



4. Let us establish a point c, three-feet below the top of stake 7, and 

 draw a dotted line from a to c, and from c to b. We have now indicated 

 the bottom of a drain that is little less than 3 feet deep at any point. 

 But it is over 5 feet deep at stake 5, and nearly 5 feet deep at stake 

 d, and these conditions, in the opinions of some persons, would call for 

 a compromise. 



5. Let us establish a new point d, 2i/^ ft. below the top of stake 7, 

 and draw a broken line from a to d and from d to b. This improves 

 matters generally from stake 1 to 7. 



6. Let us finally establish a point e, 2% ft. below the top of stake 

 11 and draw a new line from d to e, to represent the bottom of the 

 drain from stake 7 to stake 11. This materially lessens the depth of 

 digging at stakes 9 and 10. 



*7. Let us adopt the line a d e, as the bottom of drain. 

 Observe: That the drain will be 3 ft. deep at stake 1, 2^2 ft. deep at 

 stake 7, and 2i4 ft. deep at stake 11. These depths we have established 

 for convenience and economy in the work of digging. 



8. Introduce these depths in column 9 of the table — 3 ft. on line 1, 

 2.5 ft. on line 7, and 2.5 feet on line 11. 



9. If the ditch is three feet deep at stake 1, the bottom of the ditch 

 is 3 feet belQW the top of stake 1, or it is 3 feet lower than stake 1. If 

 then we subtract the depth of the ditch, 3 feet, from the elevation of the 

 top of the stake we have 7 feet as the elevation of the bottom of the 

 ditch at stake 1, above datum. Subtracting the depth of ditch, 2.5 ft. 

 at stake 7 from the elevation of 7, gives 8.74 ft. as the elevation of the 

 bottom of the ditch at stake 7. Subtracting the depth of ditch at 11 

 from elevation of 11, gives 11.70 feet as the elevation of the bottom of 

 the ditch at that point. 



10. Introduce these ditch bottom elevations into column 8 of Table 

 V on their proper lines, — 7 ft. on line 1, 8.74 feet on line 7, and 11.70 

 on line 11. 



11. Before we can go farther in finding values for columns 8 and 

 9, we must determine the fall of the drain. 



(a) The elevation of the bottom of ditch at stake 11 is 11.70 ft. 

 The elevation of the bottom of ditch at stake 7 is 8.74 ft. 



The fall of the drain from stake 11 to stake 7 is 2.96 



The distance from stake 11 to stake 7 is (500 ft.— 300 ft.) =200 ft. 



The fall per 100 ft. of this distance is (2.96 ft. -^ 2), = 1.48. 



Notice the manner in which this fall is introduced in Table VI, page 

 31. 



The stakes along this drain are 50 feet apart so that the fall from one 

 stake to another is one-half of 1.48 ft. or .74 ft. In other words the 

 bottom of the ditch at stake 10 will be .74 feet lower than at stake 11 

 and .74 ft. lower at stake 9 than at stake 10 and so on. 



*NOTE. — If this drain is to be a main drain as we are planning it may be necessary be- 

 cause of the laterals to make the line acb, the bottom of the drain. If, however, this drain 

 were to be a lateral instead of a main the line ade, would be better for the bottom of the 

 drain. 



