The Water in the Ladder is Continually Flowing Down and Out, Forming a Running 

 Stream up Which the Fish May Swim, Jumping from One Pool to the Next Higher One 



How Fish Jump 100-Foot Dams 



Do you know that fish actually jump 

 one hundred-foot dams in their 

 migrations each spring to the 

 headwaters of the rivers in which they 

 spawn? Of course, this one hundred-foot 

 jump is not made all in one leap, but in 

 a number of short leaps of eight inches 

 each. This feat is made possible by 

 what is called a fish ladder. 



This ladder must be placed in all river 

 dams in which fish such as salmon swim 

 up to the river heads to spawn. Fish 

 will not spawn anywhere except in the 

 still headwaters, and it is necessary that 

 Ihcy arrive there with the least exertion. 

 The government makes it obligatory that 

 at least one fish ladder be built into every 

 dam across such rivers. 



F"ish ladders, while they may be built 

 of wood, stone or concrete, according to 

 the material of which the dam is con- 

 structed, are all alike in ])rinciple and 

 consist of a trough which begins at water 

 level on tiie low side of the dam ami 



then extends upward in several zig-zag 

 steps to a point below the water level on 

 the up-side of the stream. Water enters 

 at the top end and flows down and out at 

 the bottom. Its flow, however, is not 

 free like that in a sluice, but is retarded 

 b\' means of cross-pieces at regular 

 intervals in the trough. 



The accompanying illustrations show 

 a reinforced concrete fish ladder built in 

 the most modern t\pe of dam of concrete 

 construction. The cross-pieces are also 

 made of concrete and form small pools 

 of water between consccuti\e ijieces. 

 Kach cross-i)iece is set at a slight angle 

 to the sides of the trough, alternate ones 

 being slanted in opposite directions. 

 Each piece has a rectangular notch cut 

 in the top and another in the bottom on 

 the opposite side. 



Alternate [)icces ha\e the two notches 

 l^laced on opposite sides, respect i\Tly, 

 as shown in the detailed iierspective 

 drawing. The trough being inclined, the 



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