598 EEPORT OF COMMISSIONER OF FISH AND FISHERIES. 



miles until it amoimts to 3 feet, wiiich may be fixed as the maximum 

 breadth required.-' 



In tbe paper from wliich this extract is made, Mr. Roberts instances 

 tbree examples of successful fisb-ways of tbe most ai)proved pattern, 

 and we may infer tbat bis conclusions were drawn mainly from obser- 

 vations on their performance, whicb was certainly very satisfactory. 

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

 taken as a basis on which to fix tbe volume of water admitted to tbe 

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

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

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

 maximum of 3 feet in width and li feet in deptb will be found insufifl- 

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

 The tbree examples given by Mr. Roberts are fisb-ways on two Irish rivers, 

 f be largestof which, tbeCorrib, drains a basin of about 1,200 square miles, 

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

 and tbe 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 discbarges, 

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

 while tbe discbarge 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. Tbe 

 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 witb tbe Corrib is not complete without a state- 

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

 of the 120,000 cubic feet flowing in summer past Galway, 100,000 are 

 drawn away above tbe dam ibr tbe use of mills aud navigation ; only 

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

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

 way, the i)assage-ways of which are 2 feet square. Evidently, tbe sal- 

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

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

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

 and I think it quite plain, iu view of these facts, tbat the size of tbe 

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

 but that the volume of water flowing over and througb tbe dam, and 

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

 considered in each individual case. Tbe consideration of so many 

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

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



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

 Wells, Sui)erintendeut Hydrographic Survey of Maine. Augusta: 1869, p. 91. 

 t Ibid, p. 106. 



