ARTIFICIAL PROPAGATION OF PACIFIC SALMONS. 



15 



connecting the spaces between the piers. These spaces, 12 in number, are 

 approximately 8 feet wide and are filled by swinging gates hinged to a 3 by 12 

 inch timber, spiked securely to the piers on either side and forming a dam or 

 flashboard across the space above. By the insertion of other tlashboards above 

 this one a tight dam 4 feet liigh can be quickly formed at any time. The 

 utility of this feature will be explained elsewhere. 



The gates are made of 1 by 4 inch fir set on edge and nailed to 2 by 4 inch 

 joists, being strengthened by 2-inch blocks set between the rack bars and nailed 

 to them and the joists. These blocks thus determine the width of the inter- 

 stices in the gates. At the upper end of eacli gate an auger liole is bored 

 through the bars and blocks, to accommodate a 2-inch iron pipe, which passes 

 through the entire upper end of the gates. Ringbolts clasp these pipes and are 

 fastened to the 3 by 12 inch timber forming the flashboard, acting as hinges 

 upon which the gates swing. At the lower end of eacli gate a wide board, IJ by 

 16 inches, is secured by means of braces, forming an angle of 45° witli the 

 lower end of the gate. 



At an ordinary stage of the stream the downstream ends of the gates rest on 

 supports which hold them a foot or more higher than the upper ends, the water 

 passing down through them to the floor of the apron, where it runs away. The 

 fish working up under the gates to the dam board find the cross passages 

 through the front end of the piers and finally reach the trap. It was expected 

 that during freshets the cuiTent acting on the flashboard would always keep 

 the lower ends of the gates above the surface of the water, and up to a certain 



Fig. 4. — Side elevation of barricade shown in figures 2 and 3. 



point this expectation was realized, but at very higli stages of the stream the 

 large quantity of gravel in the water soon clogs and sinks the gates. As the 

 gates are only two-thirds the length of the apron, however, and rise toward the 

 lower end, the water shoots over them with such force that it is projected some 

 distance below the end of the apron, and fish attempting to scale the obstruction 

 fall far short of the ends of the gates. The barrier has been watched many 

 times when fish were jumping and when the largest drift ran clear, and none 

 has ever been seen to pass it. 



By means of the dam boards entire control of the current can be had during 

 ordinary stages of water and any desired quantity sent to any section of the 

 barrier. Tims a strong current can be maintained through the trap section, 

 leading the fish to it, and when it is desired to remove the fish from the trap 

 the water can practically all be turned to some other section of the barrier. 



One of the greatest dilficulties in maintaining traps in the streams in this 

 .section is due to the tremendous quantities of gravel carried in the water 

 during freshets, a sufficient amount being frequently deposited in front of a 

 trap at such times to change the course of the stream. With the present 

 form of barrier no trouble is experienced from this source, the insertion of the 

 dam boards and the opening of one space at a time quickly clearing away the 

 accumulated gravel. 



The ninth and tenth piers were continued upstream by driving three ad- 

 ditional piles above each. The piers form the sides of the trap. Its floor is a 

 plank bottom, similar in construction to the apron, and the front is barred by 

 If-inch pickets placed If inches apart, the fish entering by the usual upstream 

 V of pickets. To protect the trap from high water the two piers between 

 which it is located were carried to a height of 8 feet. When it is desired to 

 fish the trap, the gate at its head is closed and entrance is made from below 

 by means of a door in the north side of the V. , 



