36 The Drainage of Fens mid Lozv Lands, 



CHAPTER III. 



FIELD DRAINAGE 



The object of field drainage is, by facilitating the discharge of 

 the surplus water to such a depth from the surface, that while, 

 on the one hand, it is removed so far from the roots of the 

 plants as not injuriously to affect them, yet, on the other, 

 it is not so deep as to retard, during the dry weather of the 

 summer months, the supply of moisture which will arise from 

 the substratum by the action of capillary attraction. The 

 rain which falls in summer time is nearly all absorbed by the 

 vegetation and the dry soil, or is evaporated, and little or 

 none of it soaks through the ground to the ditches. In 

 winter, however, about 60 per cent, of the rainfall soaks 

 through the ground, and is carried away by the drains to the 

 ditches and outfalls. Supposing that rain has been falling for 

 some time, that the ground has become thoroughly moist, and 

 that the pores of the earth are full of water, the rain then 

 percolates through the interstitial spaces, and by the law of 

 gravity proceeds downwards, until its progress is arrested by 

 some impermeable stratum or soil already fully charged with 

 water. It then accumulates, rising higher and higher, until it 

 arrives at a line level with the water in the river or main drain 

 of the district. This level is termed in the fens the " soc " or 

 " soak.*' 



In properly drained ground, while the rains of winter leave 

 the surface soil in a healthy moist condition, that below the 

 drains becomes completely saturated; and this supply of 

 moisture is gradually drawn up, by capillary action, to supply 

 the loss of moisture in the upper soil, which in dry weather 

 is absorbed by the roots of the plants or evaporated by 



