ARTIFICIAL. PROPAGATION OF TROUT. 13 



mining or washing out it is not wise to attempt more than a 2-foot 

 head in this way. With any bottom except one of solid ledge there 

 is always danger, and washouts are very troublesome and difficult 

 to control. Methods of dam construction and the materials used 

 must depend on local conditions. Other conditions being equal, a 

 concrete clam offers advantages in permanency and low cost of up- 

 keep. In any case a spillway to care for flood waters and avoid- 

 ance of the danger from washouts mentioned above are important 

 considerations. 



If there is a scarcity of water, or if it be desirable for aerating 

 or other purposes to secure a considerable fall, it will be advisable 

 to construct the dam on higher ground, some distance above the 

 building site, where a low dam will suffice to turn the water into 

 a conduit in which it may be carried to the hatchery at the desired 

 level. A square conduit made of planks, carefully jointed and nailed, 

 in nearly all cases is satisfactory and a small one will suffice for an 

 ordinary establishment. A thorough coating of hot tar inside 

 and out previous to use acts as a preventative of leaks and decay. 

 Pipe is generally more desirable than the conduit, and galvanized 

 iron is preferable to black. Perhaps the most durable and otherwise 

 satisfactory material for a water supply conduit for a permanent 

 establishment is wood stave pipe. Such pipe properly installed and 

 constantly carrying its full capacity gives satisfactory service for a 

 long period of time. It deteriorates when exposed and not full of 

 water. 



WATER-SUPPLY INTAKE. 



If the water supply is to be taken from a stream, and a dam 

 has been constructed to create the required head, the extension of 

 the conduit through the dam is an important point to be observed. 

 Unless this is done and the intake end of the conduit is properly 

 screened and protected there is bound to be serious trouble from 

 clogged or damaged pipes, resulting in the cutting off of the hatchery 

 water supply. 



A very satisfactory intake for meeting the conditions mentioned 

 consists of a rectangular box of concrete construction of any de- 

 sired dimensions to meet the requirements of the case. The up- 

 stream face of the dam forms one end of the box, and the shore- 

 ward side extends upstream parallel with the bank for 15 to 20 

 feet, or any required distance. The upstream end of the box is 

 projected into the stream, and the wall forming the remaining side 

 is so placed as to present an angle of 20° to the flow of the stream. 

 In this position it serves effectively to deflect ice or other drift from 

 the screen guarding the entrance to the intake. 



Between the downstream end of the outside wall of the box and 

 the dam is a space sufficiently large to permit the free passage of 

 water to the intake. This space is protected by a screen consisting 

 of a frame of 2 by 4 material of the proper size, in which is inserted 

 a grating of f-inch galvanized pipe spaced 2 inches apart. Inside 

 the inclosure thus formed, and midway between the walls, a deflect- 

 ing partition extends upstream from the dam to a point some 3 

 to 5 feet from the upstream eitd of the inclosure. This aperture is 

 guarded by a second screen placed at an angle of about 45°, the 

 bars being spaced about 1 inch apart. 



