54 How to obtain tt. 
circumstances. This screen has a very important part to play, and 
if properly fixed, will do it well. Should the bottom be unsuitable 
for driving these stakes, they must be fastened to a frame, and 
while the water is temporarily stopped, this frame may be fixed in 
concrete, which holds it firmly and prevents the water under- 
mining it, which it is very likely to do if not made secure. 
Below this leaf screen is the sluice, which is a very simple 
contrivance, and below it again is a screen for preventing the 
escape of fish. This screen may be made of wood or iron. A 
wooden frame covered with perforated zinc answers very well and 
is easily renewed, but masonry and perforated iron plates are more 
lasting. Ordinary perforated zinc has to be renewed once a year. 
In some positions it is desirable to have what we call a “horizon- 
tal leaf screen.” The term “horizontal” is perhaps not absolutely 
correct, as the screen is really placed at a slight angle, but is 
usually called a “horizontal screen” in contra-distinction from the 
‘perpendicular screen” which I have already described. 
A horizontal leaf screen consists of a box without a lid, sunk 
in the bed of a stream, and covered with perforated metal or a 
grating where the lid would otherwise lie. The box should be 
sunk so that its perforated top is even with the bottom of the 
stream, and has an easy gradient which will prevent its becoming 
easily choked. The water supply is taken from the box, under- 
neath the perforated cover or grating, by means of a pipe. Instead 
of a box, the whole may be made of concrete if preferred. This 
screen will be more fully described later on, and if made use of 
here will prove to be an impassable barrier to the fish, and will do 
away with any necessity for a sluice or a second screen. Some- 
times it is found to be easier, instead of making ponds off the 
stream, to divert the course of the stream itself, as for instance in 
a narrow valley. It amounts to pretty much the same in the end, 
being simply a case of keeping the main stream off the ponds, 
instead of the poads off the stream. The object, of course, is to 
get rid of all flood water and to have the supply for the ponds 
thoroughly under control. A reference to the accompanying 
diagram (Fig. 1) will, I think, make the arrangement sufficiently 
clear. Let AA be an embankment and KK a pond or dam above 
it. BB is the old bed of the stream, the course of which is now 
