ATKINS OX FISH- WAYS. 601 



the rivers, and a large amount going to waste, extensive milling-opera- 

 tions being rarely based on anything more than the lotc run of water. 



3. — EASE OF ASCENT. 



All the migratory fishes are capable of stemming a strong current. 

 Were the fish-way a simple, straight sluice, so that the whole volume of 

 water should pass through it without bend or break, a very high velocity 

 would be permissible. Probably six or eight miles per hour would not 

 be too swift. The Pennsylvania commissioners have erected a fisii-way 

 for shad of such a character, with a velocity whose maximum is esti- 

 mated to be ten miles per hour.* This fish-way is over a dam only 5 feet 

 high, and with a slope of 1 in 24. To construct a fish-way of this kind 

 over a much higher dam would be impracticable, because with the same 

 slope the velocity of the water would be accelerated in proportion to the 

 increase of length, and would soon become excessive ; and a more gentle 

 slope would require a structure of too great size and cost. For economy's 

 sake, both in respect to space and expense, it is deemed better to con- 

 duct the water down a steeper grade, (about 1 in 7, 10, or 15,) and 

 correct the tendency to excessive velocity by repeated change of direc- 

 tion, wliich is generally effected, in the main, by numerous transverse 

 partitions. Now, a column of water moving at the rate of ten miles per 

 hour would acquire too great a momentum to admit of such control 

 without breaking it up into a mass of tumbling spraj", in which fishes 

 would be utterly unable to direct their course. It is therefore necessary 

 to greatly modify the velocity. In Brackett's fish- way it is brought down 

 to the extremely low rate of about 100 feet per minute, which enables us to 

 turn the water at right angles without breaking the surface. In Smitli's 

 and Foster's, it is twice as great. Probablj" the maximum permissible 

 in any of the kindred styles is not above 250 feet per minute, or a little 

 less than three miles per hour. Could a fish-way be devised with a grade 

 of 1 in 10, in which the velocity should be greater without injuriously 

 breaking the water, and should fish be found to ascend it as readily as 

 hi a more gentle current, it would have this important advantage over 

 those employing a lower velocity, namely, it would discharge, in propor- 

 tion to its size and cost, a greater amount of water, and would therefore 

 be more attractive to fish. 



Lu devising means for reducing the velocity of the water, I think too lit- 

 tle weight has been given to the friction of the sides and bottom. Any 

 one who will compare the motion of water in an ordinary stony brook, 

 or a trench fish-way with that in a fish-wa^- built of timber or cut stone, 

 will be struck with the difi'erence in the flow ; in the former a much 

 steeper grade can be introduced without producing a dangerous or un- 

 manageable velocity. The cause of the difi'erence is to be sought for in 

 the conformation of the sides and bottom, particularly of the latter. In 



* Report (if the State [Peuusylvania] Coinmissiouers of Fisheries for the year ld73. 

 Harrisburg, 1874. 



