TIDAL BORE, MANTUA BRIDGE
Bore comes from an old Norse word, "bara", meaning "a wave".
(Current Tidal bore schedules) (Other tidal bore) (Current observation reports)
 
Location of observing site:
From highway 101, near Windsor, N.S., take Exit 5 to Route 14 East toward Truro. Drive for about 6 km (4 miles), just after the farm market on the right, cautiously turn left at the intersection. Immediately ahead is the bridge to Mantua, crossing the Herbert River, just off Route #14. The tidal bore can be viewed from here. Park on the wide shoulder off the highway. Be extra cautious; the traffic is quite busy on this route. View from the pedway on the bridge. The pronunciation of Mantua according to its historic origin (named for a place in Italy) is close to [man' chew-ah], however,the pronunciation in local usage is closer to [Man-away or Man - way]. Also note that some maps may mistakenly apply the name Meander to this section of the river, however, it is the Herbert River (as recorded on 1800s property deed descriptions). The Meander flows into the Herbert further upstream.
 
The view:
From the bridge pedway one is looking down stream, practically at the mouth of the Herbert River, where it merges into the St Croix River (just beyond the trees leaning out from the muddy bank on the left). Beyond, into the further distance is the St Croix River. This is the direction from which the tidal bore arrives. With keen eyes or a pair of binoculars, the wave front of the bore can be detected 7 to 10 minutes before it reaches the bridge.
 
The Bore:
About two minutes prior to the bore reaching the bridge, it divides into two parts. One section turns abruptly continuing on up the St Croix River, with its course running behind the small hill to the left. In the meantime a good portion of the flow moves into the Herbert River, flowing upstream toward the bridge. At this point, the bore may appear to die away, but this is temporary. As the tidal rush enters the mouth of the Herbert River, the wave front reforms.
 
The best photo moment is probably when the tidal front is midway between the trees and the bridge. In this run of channel, the incoming tide is more restricted by shallower water in the channel and a sandbar. A mixture of wavelengths compress into a single front, creating a nice tumbling wave across the full width of the channel (see the above photo taken from the bridge).
 
In contrast, there is deeper water in the channel just below the bridge. Watch what happens. In deeper water, the longer waves are faster and get ahead while the shorter wavelengths are slower and fall behind. The appearance of the tidal surge will change from a tumbling wave (the bore) into series of large swells, with the longest wave leading as the front surges under the bridge. All that will remain of the bore is the tumbling outer fringe in contact with the muddy bank. On days when tides are running large, the bore wave is maintained, even as it goes under the bridge.
 
Another view of the bore ( requires CAUTION!! Highway Traffic )
The bore reforms again in response to channel conditions above the bridge as it surges along the next 200 to 300 metres. In this part of its course, the channel experiences two major turns, forming an "S" in the river's shape. The expanse of marsh grasses and the dangers from the constant flow of highway traffic comming on and off the bridge make it very difficult to simply cross over and observe the tidal bore as it move on up this stretch of river.
 
To get a second view of the bore, as it progresses along the "S" turn described above, leave the pedway (turning yourself to the right), as soon as the bore goes under the bridge. You have about one minute, requiring at least a brisk walk to get as far along the guardrail as possible (the further along the guardrail to the right that one gets, the better is the view of the channel). Peering into the river channel, a nice bore can be seen as the tidal surge rounds the first bend. In the next minute the bore will go by and begin to round the second bend. If you attempt to do this ALWAYS USE CAUTION as you cross the highway along the guardrail: HIGHWAY TRAFFIC!!
 
Click here for a photo with helpful labels; click here or on the small photo for an enlargement of above photo.
 
A Tidal Bore on the Kennetcook River at Scotch Village 
Photo of tidal bore on the Kennetcook River (139 kb) as viewed from the bridge just north of Scotch Village, Hants Co., N.S.(left at Coast Gas station, 0.5 km north turning off highway 236 to North River Road). Study a highway map on how to best get from Mantua to Scotch Village.
 
The tidal bore at this location occurs about 20 minutes after the bore at Mantua Bridge. 10 km separate the two sites (a 10 to 12 minute drive).
 
More about the tidal bore:
The tidal bore in Nova Scotia is a tumbling wavefront that begins to form in the upper end of estuaries like the Avon, Kennetcook, Shubenacadie and Salmon Rivers. Over the period of 2 to 3 hours that straddles midtide, the bore may progress upstream from one river into another for a distance of 20 or 25 kilometres. During this period the Fundy tide is flooding into the Minas Basin and its estuaries at its greatest rate. The bore forms as the rapid influx of tidal water encounters the restrictions created by sandflats, the outward flow of water in shallow channels, and the nearly flat upstream gradients (click here or on photo for a closer look). The restrictions cause the variety of water waves to compress into a leading front wave moving slower than the water pushing from behind. While the faster water from behind tries to move forward in its rush to find " level", it is forced to move upward to pass over the slower moving water below. A water wall builds and quickly spills over into the tumbling, churning wave front referred to as "the bore". The height of the bore will be discussed later. The upland water flowing downstream is usually a more gentle current; it is completely overwhelmed by the rush of the incoming tide. In a moment the nature of the river is changed: the bore tumbles over itself, hissing and splashing as it rushes forward reversing the current into a vigorous upstream flow. This event marks the beginning of the new tide that will fill the river in a few hours. At bore time in the Herbert River; the tide has been rising in the Minas Basin for nearly 4 hours. The bore has travelled about 25 km (16 mi) since it begian forming in the Avon River, a little more than 1 hour and 30 minutes earlier. It may travel up the Herbert for another 5 or 6 km ( how far it reaches depends upon on the range of tide for the day) In slightly more than 2 hours, high tide will be reached. Even though there is a large variation in a given day's tidal bore times, high tide time in the Herbert River is nearly the same as high tide time for all other estuaries situated around most of Minas Basin (the variation is generally within 15 minutes).
 
Height of bore:
The word "bore" comes from an old Norse word "bara" [bah rh] meaning "a wave". A typical height for the bore as it pushes up the Herbert River would be between 15 and 60 cm (6 inches to 2 feet). Occasionally under exceptional conditions, it can be up to 1 metre (3 feet) high, licking and leaping at the steep slopes of muddy banks as it charges around a bend in the river. During tides at their lowest range (e.g. a quarter Moon at apogee), the bore can be a disappointing, barely noticable ripple.
 
Changes in the tidal bore
Along the course of the river bottom, its profile and depth can vary considerably, bringing about continuous change in the appearance and height of the bore as it moves forward. Where the water is deeper, the tumbling water wall collapses into a pattern of water waves; the longest wave lengths travel faster and move ahead leaving a sequence of shorter waves trailing behind. Where it is shallow and flat, the leading front of water slows, shallow water waves bunch up as faster water behind rushes forward creating a new wall of tumbling water (the bore). Whether weak or strong, once the front running wave of the incoming tide goes by, the current running upstream is significently stronger than the current that had been flowing downstream. For the next 2 hours (when high tide is reached), millions of litres of sea water will flow inland and upstream to fill the river and overflow into the green tidal marshes above the muddy banks. By the time the level of the tide reaches the grasses its current will have slowed. At high tide the current comes to a standstill, over a period of 2 or 3 minutes the flow gradually reverses and water levels immediately begin to drop. In about 4 hours the river will empty approximately to its prebore level, a much gentler process than was the rush of the incoming tide.
 
The best tidal bore conditions:
The best tidal bore is produced when a large volume of tidal water is flowing up the river against a small downstream volume and the river gradient is nearly flat.. Vigorous tides, with the highest volume of water, are produced in association with New and Full Moon, called Spring Tides (nothing to do with the season). The tide producing forces of both the Sun and Moon are synchronized. An even greater enhancement for larger tides results when perigee (Moon is closest to Earth) is on or near a Full or New Moon. Tides that occur with a Quarter Moon have lower volume and are "lazier" (Neap Tides), solar and lunar tide forces are not acting together. Because there is a lag in time between energy input and the resulting output, the tidal bore on the largest tide is generally a day or two after a Full or New Moon (study the range section of one of Sherm's tide Charts).
 
Other tidal bores:  
A Tidal Bore on the Kennetcook River at Scotch Village 
Photo of tidal bore on the Kennetcook River (139 kb) as viewed from the bridge just north of Scotch Village, Hants Co., N.S.(left at Coast Gas station, 0.5 km north turning off highway 236 to North River Road). Study a highway map on how to best get from Mantua to Scotch Village.
 
The tidal bore at this location occurs about 20 minutes after the bore at Mantua Bridge. 10 km separate the two sites (a 10 to 12 minute drive).
A Tidal Bore on the Salmon River (Truro)
Photo of tidal bore on the Salmon River in Truro, N.S. taken August 23rd, 2004. At the Palliser on Tidal Bore Rd near exit 14 off highway #102. The Truro tidal bore happens about 1 hour before Minas Basin high tide given in the schedules below. A website with Truro and Maccan tidal bore times.
  
Schedule of Predicted Times
 
Mantua bridge, near Brooklyn, Hants Co, N.S. Bore times are approximately 4 hours after Windsor low tide. Weather conditions, changes in currents and river channels can speed up or delay the time of the bore arrival. So arrive at least 10 to 15 minutes before the predicted time and be patient.
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