Tidal Bore Notes for the Schedule at the Mantua bridge

( Index of schedules)

There are approximately two tidal cycles per day which can produce a tidal bore, however, the tidal bore schedule of predictions posted at this site give only the tidal cycle containing the most convenient daytime tidal bore that occurs between low and high tide at the bridge near Mantua, Hants County (15 minute drive from Windsor, N.S.). For the days when two tidal bores happen in daylight, a second schedule has been added as an alternative time for viewing the bore.

When the tidal bore arrives at the Mantua bridge, it marks the beginning of the rising tide in this part of the river. Up to this time the tide has been flooding into the Minas Basin, its inlets and estuaries for almost 4 hours. It has progressed up 3 rivers to reach Mantua bridge, entering first, the mouth of the Avon at Horton Bluff. 15 km further up the Avon, the tide entered the mouth of the St. Croix, situated between the Information Centre at Windsor and the wharf at Newport Landing (near Avondale). For about two more hours it progressed up the St Croix River until part of it was diverted into the Herbert River just minutes before it rushed under the Mantua bridge. The total river distance described here is about 25 km (16 mi).

 

High tide occurs about 2 hours and 10 minutes following the bore arrival at the bridge at Mantua. Even though it takes between 3 and 4 hours, or more, for the first pulse of the incoming tide to reach a given point along the system of rivers, high tide is reached near the same time all along the shorelines and estuaries at the southern and eastern ends of Minas Basin (differences for time of high tide at most places are less than 15 minutes).

 

With binoculars you can see the bore in the far distance working its way up the channel as early as 10 minutes before it reaches the bridge. In this stretch of river channel the bore advances at a rate of about 8 km per hour.

This schedule was developed so that the actual arrival of the bore will tend to be later than the prediction rather than earlier. Times for the bore given in the schedule average 10 minutes earlier (more or less) than when the bore will actually pass under the bridge. The bore is the leading edge of the new, incoming tide.

Variables difficult to predict do alter the timing of the tide's progress causing the bore to arrive earlier (and later!) than expected. A variation of 20 minutes can occur under some conditions.

 

The range, in metres, given in the table indicates the vertical rise of water from low water in the Minas Basin at the time of Low Tide, to high water at the time of High Tide. The volume of tide water flowing into the Minas Basin produces the best tidal bore activity when tide range is large (13 to 15+ metres). In the posted schedule, the range highlighted in red indicates best range for the bore performance.

 

A typical height for the bore is 20 to 40 cm, but when tidal range is large, a very vigorous tumbling wave 60 or 70 cm high can occur. When tide range is less than average (under 10 metres), bore activity is less dramatic; it can even be a disappointing ripple that may be barely noticable. Strong or weak, the tidal bore will always decisively reverse the river current so that it runs vigorously upstream. For more information about the bore, click here.

 

 

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