Sscrmon LIÉE, 1911. .. [123] Trans. R. S. C. 
PROGRESS OF THE TIDE IN DEEP INLETS: AND ORDINARY ESTUARIES. 
By W. Bezz Dawson, M.A., D.Sc., M.Inst.C.E., F.R.8.C. 
(Read May 17, 1911. 
We desire to draw attention to some features in the progress of 
the tide in estuaries and inlets which may not have been adequately 
recognized. The progress of the tidal undulation up an estuary is 
usually compared to a wave rolling inshore over a shallow beach, before 
it breaks. Progression of the tidal undulation in this manner takes 
place only in estuaries which are shallow, however. We have now 
observations to show that when the estuary or inlet is deep, say 100 
fathoms, the rise and fall of the tide is practically simultaneous over 
the whole area. 
Shallow Estuaries.—(1) Rate of Progress. In ordinary estuaries 
the time of high water is later at successive points; and for low water 
the difference in time is greater because the trough of the undulation 
always moves more slowly than the summit when the amplitude is any. 
large proportion of the total depth. It is this retardation of low water 
which modifies the symmetry of the undulation and steepens its for- 
ward slope, making the rise of the tide more rapid than the fall as it 
passes any given point. The undulation may thus ultimately break 
and become a Bore, as it does in the Petitcodiac river at the head of 
the Bay of Fundy. 
These conditions are well illustrated by the inner part of the 
estuary of the St. Lawrence, from Father Point to Quebec. The 
same conditions obtain in deep bays, such as Chaleur bay; and possibly 
in some straits, especially those which narrow rapidly towards one end. 
The following examples are based on simultaneous observations, taken 
day and night to eliminate diurnal inequality; and all the differences 
are in absolute time. The larger time-intervals in the case of low 
water are noticeable. 
St. Lawrence Estuary. For H.W. For L.W. 
Father Point to Orignaux Point. Distance 103 miles. 
Average Spring range for the two places, 16 feet...| 1h. 35m. | 1h. 48m. 
Orignaux Point to Quebec, Distance 77 miles, Spring 
PAUDE AS (00h22 weet: die done sam me oo si desc ses se 2h. 45m. | 3h. 45m. 
(2) Variation in the time-interval. The interval of time in the 
progress of the tide from the mouth to the head of an ordinary estuary 
Sec. III., 1911. 9. 
