600 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



send the greater part of the water off into canals to feed mills. This 

 circumstance, so far from being anything to regret, is of positive advan- 

 tage, since it lessens the volume of water required in the fish-wav. 



Besides the necessity of a sufiScient volume of water to attract tish 

 into the fish-way, it must be deep enough and wide enough to afford 

 tliem ample room for movement while ascending it. The hitter deside- 

 ratum may sometimes dictate the capacity of the structure in small 

 streams; although, in rivers of considerable size, there can be no diffi- 

 culty in this respect if due care is taken to meet the imperative demand 

 for an attractive discliarge of water. Salmon can, and sometimes will, 

 pass through an opening much less than a foot square ;* and if there be 

 cases where so small an opening will discharge a flood duly attractive, 

 these dimensions will suffice. Under the same limitations, the passage- 

 ways of a fish- way designed for the use of alewives only may be reduced 

 to six inches square, discharging not over 40 cubic feet of water per 

 minute. 



The dimensions given are adapted to the form of fish-way known as 

 Smith's, and to those which, like it, afford a very free passage to the 

 water. Of this kind are Foster's and the fish-ways in use in Maine 

 rivers before his were introduced. Those devices which greatly retard 

 the water, such as Brackett's, will require a corresponding enlargement 

 of the openings. 



In devising fish-ways for shad, an entirely different scale must be 

 adopted. The lack of a sufficient volume of water is doubtless the prime 

 reason why shad have never freely ascended any fish ways, except the 

 two remarkably wide ones constructed at Columbia on the Susquehanna 

 Eiver, which give passage to from 20,000 to 50,000 cubic feet of water 

 per minute. 



The wants of the fish alone fix the minimum capacity of the fish-way ; 

 but in determining the proper maximum, we must consult the interests 

 of the owners of the water-power, who generally bear the burden of con- 

 struction and maintenance, and who are therefore affected both by the 

 cost of the structure and by the amount of water withdrawn by it from 

 the use of the mills or canals. The cost, which is the most important 

 point by far, will be considered in another place. Serious intrench ment 

 on the water-supply is not likely to occur, for the following reasons: 

 first, the amount of water required need not exceed one-fiftieth of the 

 average volume of the river ; secondly, the extensive use of the water for 

 mills or navigation generally greatly reduces the volume passing over 

 the dam and down the main channel by which the fish approach the 

 fish-way, and warrants a corresponding reduction of the amount of water 

 needed; thirdly, the period during which it is desirable to operate the' 

 fish-ways is at a date when there is generally an abundance of water in 



* At Bucksiiort, sahiiou have passed in considerable unmbers down througli an o|ieu- 

 ing eiglit inches wide and less than a loot deep in attempting to reach a spawuiug- 

 ground in a brook. 



