Table No. 2 shows the rise of the slope for 100 feet of its own length. If the sloping line, (at an angle of 15°,) is 100 feet long, it rises 25.882 feet.
| TABLE No. 1. | |
|---|---|
| Deg. | Feet. |
| 5 | 8.749 |
| 10 | 17.663 |
| 15 | 26.795 |
| 20 | 36.397 |
| 25 | 46.631 |
| 30 | 57.735 |
| 35 | 70.021 |
| 40 | 83.910 |
| 45 | 100.— |
| 50 | 119.175 |
| 55 | 142.815 |
| 60 | 173.205 |
| 65 | 214.451 |
| 70 | 274.748 |
| 75 | 373.205 |
| 80 | 567.128 |
| 85 | 1143.01 |
| TABLE No. 2 | |
|---|---|
| Deg. | Feet. |
| 5 | 8.716 |
| 10 | 17.365 |
| 15 | 25.882 |
| 20 | 34.202 |
| 25 | 42.262 |
| 30 | 50.— |
| 35 | 57.358 |
| 40 | 64.279 |
| 45 | 70.711 |
| 50 | 76.604 |
| 55 | 81.915 |
| 60 | 86.602 |
| 65 | 90.631 |
| 70 | 93.969 |
| 75 | 96.593 |
| 80 | 98.481 |
| 85 | 99.619 |
With the maps before him, showing the surface features of the field, and the position of the under-ground rock, the drainer will have to consider the following points:
1. Where, and at what depth, shall the outlet be placed?
2. What shall be the location, the length and the depth of the main drain?
3. What subsidiary mains,—or collecting drains,—shall connect the minor valleys with the main?
4. What may best be done to collect the water of large springs and carry it away?
5. What provision is necessary to collect the water that flows over the surface of out-cropping rock, or[pg 058] along springy lines on side hills or under banks?
6. What should be the depth, the distance apart, the direction, and the rate of fall, of the lateral drains?