and the Storage of Water. 
29' 
quantity of land occupied by the stream, if it were made large 
enough to receive the whole of the water sent down in these 
floods within its proper bed. To meet this the banks may be 
placed some distance apart, and the " cess," or intervening space 
between the foot of the bank and the stream, be laid at a very 
flat slope, and grassed over. In excessive floods the whole space 
between the banks would thus afford water-way of sufficient 
capacity to meet the most extreme rainfall. During the rest of 
the year it would afford excellent pasturage for sheep and cattle. 
The bridges and other works must be made of the full dimen- 
sions to meet the largest floods, so that the water should have 
free course and meet with no impediment. 
Flood-gates and Sluices. — While embanking shuts out the 
flood-water from flowing over the adjacent lands, it also pre- 
vents the drainage from these low lands finding access to the 
main water-course. Provision can be made for this by cuttings 
an interior drain, running parallel with the bank and dis- 
charging lower down the stream. If, however, the floods only 
occur at long intervals and last a short time, the low-land 
drains which enter the main stream may be protected by 
sluices with fixed or self-acting doors. The latter would close 
by the action of the water as soon as the level outside became 
greater than that inside, and open again for the emission of 
the inland water as soon as the flood had passed off". By 
a judicious management of these sluices the land behind the 
banks can be kept well drained. If the sluices have fixed doors, 
the person under whose care they are placed, as soon as a 
heavy rain comes, ought, in anticipation of a flood, to open the 
door and empty the drain, which would then become a reservoir 
to receive and hold the water percolating from the rain on the 
low land until the height of the flood had sufficiently subsided io 
allow of the doors being opened. The best form of sluice has 
a double set of doors, the one self-acting, and the other so fixed 
as to regulate at pleasure the height of the water in the drains. 
The engraving (Fig, 3, p. 30) represents one of these sluices 
with a lour-feet opening and self-acting tankard-lid door, with 
draw-door behind. 
In tributary streams, self-acting doors, shutting against the 
river into which they drain, are often very beneficial in prevent- 
ing the backing-up of the water in heavy floods. By their use 
many miles of embankment may be saved. Even where em- 
bankments exist, the erection of doors saves great pressure and 
the consequent risk of a breach, a contingency from which no 
banks are free. Some settlement, or weak place in construction, 
or burrow made by mole, rat, or rabbit, which may have been in 
existence for years unknown, is finally discovered by a flood a 
