14 
Trunk Drainage. 
rate, as the stream cannot receive back its water from the under- 
drains until it has itself subsided to a sufficiently low level, the 
drains are powerless to emit their contents when it is most of all 
required. Of course, with an unruly outfall the chief benefits of 
subsoil-drainage can never be obtained ; and when river meadows 
have been improved by this means, it has been by previously 
providing some contrivance, such as a " back-drain," on a lower 
level than the stream, and emptying into it at a point farther 
down the valley. Generally speaking, where mills or canals have 
deprived us of the fall of a river, they have so successfully 
appropriated all the " power" inherent in the descent as to 
leave no adequate fall for good drainage, or even dam up the 
water-line to the ditch brinks, which law will not allow them 
to perpetually overflow. Without laying again the foundations 
of the principles and practice of under-draining, I may point out 
some of the injuries arising from its denial to these districts. 
First, as to the Grass-land, of which the surface principally 
consists. Conclusions deduced from practice upon artificial 
water-meadows are equally applicable to other low lands supplied 
with a superabundance of water. Hence, it being fully proved 
that the best water-meadows are those possessing an open and 
porous subsoil, or else the alternative of a competent system of 
under-drains, combined with a proper outfall for the oozing 
water; that floods of most fertilizing properties injure the vegeta- 
tion when retained within or upon the surface of the soil beyond 
a certain period ; and that a circulation of water through the soil 
is as essential to profitable irrigation as a current over it— we 
may declare that any river-meadow devoid of these elementary 
conditions of prosperous vegetable growth cannot be in a fit state 
for the exercise of good husbandry. In the upper part of the 
valley of the Nene, above Northampton, there are many hundred 
acres of fine meadow land greatly lessened in value, because the 
undue height at which the river is kept prevents the smaller 
streams, into which the under-drains should empty themselves, 
from having any outfall. This causes these under-drains to be 
useless for nine months in succession, and sometimes for the whole 
year. And in vain are the brooks and small water-courses 
widened and deepened ; for, having no natural scour from a 
current, they speedily choke again with weeds, rushes, and mud. 
The bad condition of the river has grown, of course, since these 
meadows were first subsoil-drained ; and thus all the farmer's 
attempted amelioration is lost upon his grass, because the noxious 
bottom-water cannot be discharged. In this valley it is com- 
monly found that such patclies of a tract of meadow-land as have 
the good fortune to possess a gravelly subsoil, through which 
almost any quantity of water will drain off, seem to be enriched 
