Draining for Profit, and Draining for Health. George E. Waring

But when we have got rid of the cold arising from the evaporation of free water, have given a range of several feet to the roots of grass and cereals, and have enabled retentive land to filter through itself all the rain which falls upon its surface, we are not, in our present state of knowledge, aware of any advantage which would arise from further lowering the surface of water in agricultural land. Smith, of Deanston, first called prominent attention to the fertilizing effects of rain filtered through land, and to evils produced by allowing it to flow off the surface. Any one will see how much more effectually this benefit will be attained, and this evil avoided, by a 4-foot than a 2-foot drainage. The latter can only prepare two feet of soil for the reception and retention of rain, which two feet, being saturated, will reject more, and the surplus must run off the surface, carrying whatever it can find with it. A 4-foot drainage will be constantly tending to have four feet of soil ready for the reception of rain, and it will take much more rain to saturate four feet than two. Moreover, as a gimlet-hole bored four feet from the surface of a barrel filled with water will discharge much[pg 071] more in a given time than a similar hole bored at the depth of two feet, so will a 4-foot drain discharge in a given time much more water than a drain of two feet. One is acted on by a 4-foot, and the other by a 2-foot pressure."

      If any single fact connected with tile-drainage is established, beyond all possible doubt, it is that in the stiffest clay soils ever cultivated, drains four feet deep will act effectually; the water will find its way to them, more and more freely and completely, as the drying of successive years, and the penetration and decay of the roots of successive crops, modify the character of the land, and they will eventually be practically so porous that—so far as the ease of drainage is concerned—no distinction need, in practice, be made between them and the less retentive loams. For a few years, the line of saturation between the drains, as shown in Fig. 11, may stand at all seasons considerably above the level of the bottom of the tile, but it will recede year by year, until it will be practically level, except immediately after rains.

      Mr. Josiah Parkes recommends drains to be laid