Trunk Drainage. 
35 
difficulties of an improved Trunk Drainage, commencing with 
the question contained in the heading No. 7, viz. the requisite 
moisture of suhsoil in existiiiq meadows, and water for irrigation. 
It is not to be received as an infallible rule that the water of open 
drains, any more than of under drains, may always be kept 3 or 4 
feet lower tlian the surface of all kinds and conditions of soils ; 
there being many subsoils which are drained and sub-irrigated to a 
great extent merely by means of the division ditches of the fields. 
And there are many meadow and grass lands in the south and 
east of England which may be easily over-drained. Mr. Pusey 
mentions (Journal, Vol. XI. p. 403) a field of good land in the 
south which was so much injured by under-draining too thickly 
that the grass became of inferior quality, as was proved by its 
requiring only three days instead of four to make into hay, the 
effect of impoverishment in the sap of the grass. " On my own 
meadows," he says, " I have adopted the plan of damming the 
streams in summer. The water in the land consequently does- 
not escape from the land, whilst the stream finds its way up the 
drains, and rises as in a sponge ; so that this kind of sub- 
irrigation keeps the bottom cool and the surface green, while 
other meadows are scorched by the summer sun." It is well 
known by the Lincolnshire graziers, that bullock pastures have 
become mossy, and degenerated into sheep-land, merely by too 
much drainage; and on some of the peaty lands good arable has 
grown weaker from the same cause. The hardening and gaping 
of the clay, the loosening and honeycombing of the light arable 
soil, and the burning of pastures in general, may arise from 
undue saturation previous to the drying ; and sub-irrigation 
might be circumscribed within smaller districts if, by a perfect 
command of the water, they could insure a minimum in winter 
and a wholesome quantity through the summer. The necessity 
of attention to this point being admitted, it will of course be for 
each local drainage district, under proper regulations, to determine 
its own supply, and lay out works according to the volume and 
irregularity of the river water, the downfall, or the sprins^s 
peculiar to the situation. 
In providing for irrigation, there can be no greater difficulty 
than that which must be overcome in order to improve the 
drainage, as, where a freer passage and greater inclination of the 
stream has been obtained, a system of " back-drains," " catch- 
water-drains," and other works, might soon be added to facilitate 
the flooding of water-meadows. In some cases it will be a diffi- 
cult matter to determine the relative quantities of water which 
may be allowed to be abstracted from the main channel for 
watering or for irrigation. In Italy it is measured out through 
apertures of certain calibre, with a uniform pressure of water 
d2 
