54 How to obtain it. 



circumstances. This screen has a very important part to play, 

 and if properly fixed, will do it well. Should the bottom be un- 

 suitable 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 

 undermining 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 wihout 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 ponds 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. i) 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 



