598 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



miles until it amoimts to 3 feet, which may be tixed as the maxiinuin 

 breadth required." 



lu the paper from which this extract is made, Mr. Roberts instances 

 three examples of successful Ush-ways of the most approved pattern, 

 and we may infer that his conclusions were drawn mainly from obser- 

 vations on their performance, whicli was certainly very satisfactory. 

 Yet, if the size of the drainage-basiu, or the volume of the river, be 

 taken as a basis on winch to fix the volume of water admitted to the 

 fisb-way, it is hard to see why the ratio between them should not be con- 

 stant, or why the size of the fish-way should be limited while the size of 

 the river continues to increase. It is quite probable that Mr. Roberts's 

 maximum of 3 feet in width and li feet in depth will be found insuffi- 

 cient for the passage-ways of fish-ways on our larger American rivers. 

 The three examples given by Mr. Roberts are fish-ways on two Irish rivers, 

 the largestof which, the Corrib, drains a basin of about 1,200 square miles, 

 about the size of the basin of the Saint Croix. Between the Saint John 

 and the Hudson are six or seven rivers with larger drainage-basins than 

 that. The Kennebec drains 5,800 square miles; the Penobscot, 8,200; 

 and the Connecticut, over 10,000. In point of volume, however, there 

 does not appear to be so great a disparity. The Corrib discharges, 

 during the summer-season, 120,000 cubic feet of water per minute, 

 while the discharge of the Kennebec at Augusta is estimated at only 

 380,000 cubic feet per minute through the year;* being probably quite 

 up to the average during May and June, when fish are ascending. The 

 Connecticut, at Turner's Falls, in the winter of 1866, discharged at 

 various times from 300,000 to 600,000 cubic feet per minute.t The com- 

 parison of these rivers with the Corrib is not complete without a state- 

 ment of the peculiar way in which the water of the latter is used. Out 

 of the 120,000 cubic feet flowing in summer i)ast Galway, 100,000 are 

 drawn away above the dam for the use of mills and navigation ; only 

 the remaining 20,000 flowing over the dam and down the main channel. 

 Of this small residue, 720 cubic feet (being ^^) flow through the fish- 

 way, the passage-ways of which are 2 feet square. Evidently, the sal- 

 mon, having followed the main channel up to this dam, will much more 

 readily find the fish-ways than they would if the entire volume of the 

 river were pouring over the dam. Such will be the case in every river, 

 and I think it quite plain, in view of these facts, that the size of the 

 drainage-basiu is not a safe basis on which to fix the size of the fish-way, 

 but tliat the volume of water flowing over and through the dam, and 

 the amount discharged from the mills in its immediate vicinity, must be 

 considered in each individual case. The consideration of so many 

 diverse circumstances will, of course, prevent the strict application of 

 any rule; but it may, nevertheless, be instructive to observe the dimen- 



* 200,000,0n0,000 cubic feet per aunum.— The Water-Power of Maine, by Walter 

 Wells, Superinteudeut Hydrograpbic Survey of Maine. Augusta: 1869, p. 91. 

 t Ibid, p. 106. 



