Sbction III., 1909. [ 1"9 ] Trans. R. 8. C. 



X. — Effect of the Wind on Currents and Tidal Streams. 



By W. Bell Dawson, M.A., Ma.E., D.Sc, M.Inst.C.E., F.R.S.C. 

 Superintendent of the Tidal and Current Survey. 



In discussing the question of the influence of the wind on tides and 

 currents, it is first necessary to make a clear distinction between the 

 effect of the wind on the rise and fall of the tide, and its effect in 

 increasing or retarding the horizontal motion of the water and disturb- 

 ing the normal movement which would otherwise prevail. 



The influence of the wind and barometer in modifying the height 

 of the tide has been carefully studied, especially in Holland where it 

 is of tlie lir?t importance; and in England, the British Association ap- 

 pointed a committee to investigate the question, which published a report 

 in 1896 on the Effect of Wind and Atmospheric Pressure on the Tides. 

 We do not propose to take up this side of the matter ; but would only draw 

 attention to the excellent opportunity for the study of the subject which 

 the St. Lawrence estuary affords. It is one of the largest estuaries in 

 the world, with a tide of only five or six feet at its mouth, increasing to 

 nearly 20 feet at its head. A large amount of material is now available 

 for the purpose ; as the Tidal and Current Survey has now accumulated 

 record from registering tide guages continuously during 14 years; and 

 with this, complete meteorological observations are available for com- 

 parison. 



With regard to the influence of the wind on the horizontal movement 

 of the water, which for clear distinction we designate comprehensively as 

 Current, there appears to be extremely little information available. The 

 general oceanic circulation is very often ascribed to wind influence; but 

 whether this is the dominating cause relatively to other influences, is 

 probably still open to discussion. It is also difficult to obtain satisfactory 

 information from vessels, as during storms they cannot usually distin- 

 guish between their leeway and the drift which is due to the movement 

 of the water itself. 



It may, therefore, be of value to bring together in one concise sum- 

 mary the results which have been secured during the course of this Sur- 

 vey, and to explain the methods by which these results have .been obtained. 

 The currents have now been investigated throughout eight seasons of 

 four months each, and the regions investigated include the Gulf of St. 

 Lawrence, the Bay of Fundy, Belle Isle strait, and localities in the open 

 Atlantic off JSTova Scotia and Newfoundhand, as far as 20 or 25 miles 

 from shore. 



