44 The Drainage of Fens and Low Lands. 



iron grating before the mouth of it to prevent the vermin 

 from getting up ; and too much care cannot be bestowed in 

 keeping these outfalls clean and free. 



Direction and Fall.— Drains should always be laid to 

 run with the fall of the land, and not across it. A different 

 theory was held for a short time by some drainers, but 

 practice has proved what theory would teach, that the drains 

 should fall with the land, the only exception being in the 

 case of springs. A consideration of the subject will show that 

 the water has the least distance to travel to the drains when 

 laid in this manner, and when there will get away most 

 quickly. Supposing the strata to have the same inclination 

 as the surface, and the drains to be laid 30 feet apart, the 

 water will of necessity flow in the direction of the strata, 

 and a pait of it must therefore travel 10 feet if the drains be 

 laid to run across the slope ; but, on the other hand, if they 

 be laid to run with the inclination, the water will flow from 

 the centre space between the drains in both directions, and 

 thus have only 15 feet to travel, or only half the distance. 



Where a field is in one plane, and level throughout, it is 

 better to lay the main across the centre of the field, letting 

 the drains radiate from it at right angles towards the sides- 

 The object to be kept in view is that the drains may be placed 

 so deep, that while rapidly collecting and conveying away the 

 suiplus of the rainfall, they shall also be so situated as most 

 effectively to promote a circulation of air, and allow the 

 moisture to be drawn up from the subsoil below the drains to 

 the roots of the plants in dry weather. Where no special 

 circumstances arise to prevent it, this object seems to be 

 most effectively attained where there is a covering of 3 feet 

 on the top of the drain pipes; and this may be taken 

 as a safe depth to lay drains, whether in tenacious clays or 

 silts and more porous soils ; and from 8 yards to 9 yards apart 

 in the former class of soils, and from 10 yards to 12 yards in 

 the latter, is sufficient distance for the drains to act effectively. 



