BY OPEN Oil COVERED DRAINS. 255 



leaving so little space between, that trees cannot sufficiently spread 

 their roots, and are thereby liable to be overthrown by wind. When, 

 therefore, that interspace (24 feet) is too great for open drains 2 

 feet deep, it would be preferable to have covered drains, rather than 

 open drains of that depth, closer to each other, or the ground may 

 be intersected say every 50 or 60 yards with open drains 4 feet deep, 

 running into a leader or main drain 3 inches or so deeper, with 

 open drains 2| or 3 feet deep, and 30 feet apart between the 4 feet 

 drains. If merely surface water is to be removed, and the soil is of 

 a retentive nature, drains 18 inches deep and 20 feet apart may 

 produce the effect without adding to the cost. On the other hand, 

 when open drains are cut at a greater distance apart than 40 feet, 

 even if 3 feet deep, they have little effect in removing either bottom 

 or surface water from the centre of the intervening space, and in 

 land requiring so little drying, a few well laid out drains 2 feet deep 

 may answer the purpose. Open drains 4 feet deep alone, at the 

 required distance apart for the draining of wet ground, are objection- 

 able, on account of the great width at top required to keep them 

 from falling in, and they are otherwise inconvenient and costly. 



The direction or line in which drains are run, so as to produce 

 the best and immediate effect, by the removal of stagnant water, &c, 

 must depend on the natural lie or fall of the ground. Main drains 

 or leaders should always be made in the lowest parts of the ground, and 

 have as free an outlet as possible. Too great a fall should, however, be 

 avoided, as the water received from the sub-drains after heavy rains 

 acquires such force as, in the case of open drains, is liable to damage 

 the sides or bottom. "When, therefore, the ground is hilly, or has a 

 steep slope, with an extent of level land at the bottom, a main or 

 leader or sub-leader drain may be cut along the bottom, so as to 

 drain the level ground, and another for the reception of the water 

 from the slopes. Without such an arrangement, if there is much water 

 running in the small drains down the slope, it will flow with great 

 force to the bottom, and run more slowly on the level portion, 

 thereby any soil or sediment carried down by current is left on the 

 more level part from the want of force to carry it to the outlet, 

 filling up and choking both open and covered drains in the course 

 of one or two seasons. But by having a main drain for each portion 

 this is avoided, as the greater run of water in the main drain from the 

 small ones carries any sediment from the slopes towards the outlet. 

 Many opinions exist as to the direction in which small drains, 

 whether covered or open, should run. For a long time, and until 



