SECTION III, 1916 [71] RRANS eS Gs 
The Turn of Tidal Streams in Relation to the 
Time of the Tide. 
By W. BELL Dawson, M.A., D.Sc., M.Inst.C.E., F.R.S.C. 
Superintendent of the Tidal and Current Survey. 
(Abstract of Paper read before Section III of the Royal Society of Canada, at May 
Meeting, 1916.) 
When the tidal undulation of the ocean enters estuaries or inlets 
on a coast, it not only causes a vertical rise and fall of the water 
surface, but also a horizontal movement of the water in reversed 
directions, known as tidal streams. The object of this paper is to 
discuss the time-relations between these two movements, with illus- 
trative examples from the Eastern and Pacific coasts of Canada, which 
afford a specially good field because of the great variety in their 
types of tide. These examples were selected as a basis for the explana- 
tion of the subject; but in the present abstract they are merely cited. 
The time-relation between high water and slack water, when 
the tidal stream is reversed in direction in estuaries, straits and inlets, 
is highly important to the mariner; but the discussion of the problem 
of the time-movements of tidal streams has been very restricted so 
far, chiefly for want of a clear classification of the conditions presented 
by the various types of inlets and estuaries. 
For the purposes of the mariner, if a constant difference of time 
is determinable, between the time of high or low water and the time 
at which the current reverses its direction, the problem is solved; 
but if the time-relation is more complex, special tables of Slack Water 
must be calculated. A practical distinction must also be made ac- 
cording to the swiftness of the current. If the tidal flow is sufficiently 
moderate to allow of navigation at all times, it may answer the pur- 
pose to give data for the time of maximum current; but if the swiftness 
of the current makes navigation perilous or even impossible except at 
slack water, it is essential to know the time when the slack occurs. 
Hence in solving the problem, it may be either the moment of Maxi- 
mum current or of Zero current that requires correlation with the time 
of the tide. 
Classification.—In dealing with these questions, it is necessary to 
distinguish clearly the various characteristics of estuaries, straits 
and inlets, aswell as the different types in the tide itself. There is 
to begin with, a condition under which there will be no current in 
