Peggy's Cove: Waves from the East?

Prepared by Doug Mercer
Research Meteorologist, Maritimes Weather Centre
October 17, 2003

The Event

Near midnight September 28/29, 2003, the fishing village of Peggy's Cove, NS, was flooded by a series of waves over the space of half an hour, due to the onslaught of Hurricane Juan. The strange thing about this event was that the waves hit the village from the east, while the village harbour is exposed only to the west. This wave came over 300-400 metres of land. While doing so, it rose over a low 5-metre ridge, then had to go over a wall nearly 2 metres high, for a total rise of over 7 metres.

Description of Event

This description comes from a combination of witness reports, going over the territory and looking for physical evidence, and aerial photographs of the area affected. The main witnesses were John Campbell, the President of the local Harbour Authority, and a local businessman named Roger Crook who owns part of the property affected.

As the hurricane approached, the winds increased rapidly from the east. At the same time, the combination of high tide (albeit the lower of the two daily high tides), spring tide (the peak in the monthly tidal cycle associated with new and full moons), and perigee (the closest approach of the moon to the earth during the monthly orbit) increased the water level inside the harbour until it was near the level of the government wharf. Roger Crook was near the harbour, but left between 11:30-12:00 p.m., ADT, as the winds became dangerously high. Soon after this John observed a wall of water 4-5 feet high approach the harbour from the downward sloping valley to the east. The water flowed across the road and into the harbour, heavily damaging a garage and causing elevated water levels and strong currents in the harbour.

The flow of water down the valley would diminish gradually to a foot or two in depth, then another pulse of water would come, looking much like a tidal bore. This happened 6-12 times in 20-30 minutes, then trickled away to nothing.

Damage Done

This is a partial list of the accounted damage:

• The foundation under a gift shop was undermined by the flow of water. A garage was badly damaged, probably by the first wall of water.
• The deck of the government wharf was lifted and twisted by the rising water and strong currents associated with the waves.
• A driveway was destroyed and had to be replaced. A large part of the road in the path of the wave was eroded (although the main roadbed remained usable).
• The eastern portion of the parking lot of the restaurant nearest the lighthouse became flooded and large boulders (300-500 pounds) near its edge had been moved by the water.
• People on the north side of the wave were trying to retrieve items caught in the flow, but were only partially successful due to the large width of the flow, and also due to the 6-12 pulses, or bores, making the people retreat from the flow.

Partial Explanation

The wave events were likely due to a combination of unusually high water levels, extremely large swell from the hurricane, and an unfortunate arrangement of the topography.

Figure 1 will help us understand what happened. This is an aerial photograph taken in 2002. Location 1 shows an area where water can enter the valley west of it fairly easily, especially during high water levels and with large waves. This valley has two branches, one going west towards the lighthouse (6) and the restaurant parking lot (7). The second, and more important branch, goes up a 5-metre rise and then down a slope into the harbour. The breakwater (2) was built in 1915 and is somewhat unusual, being about 200 metres from the nearest body of water. Clearly, this shows that flooding due to waves from the east has happened before-often enough to require this structure. It is important to realize that since the construction of this breakwater, it has been reasonably effective . . . until Hurricane Juan.

Here is the basic picture. Water level rises and large waves coming from the east or southeast combine to fill up the eastern valley, which can only drain slowly. This increases the sea level for approaching waves. Eventually the largest of the waves making it into the valley can make it over the breakwater and pour down into the harbour like a wall of water. Approaching waves do not have to be as large because of the higher levels to the east of the breakwater from the first large wave. Finally, a combination of falling tides (high tide was near 10:45 p.m.), rapidly dropping storm surge, and weakening storm swell allows the valley to drain and the danger to end.

There are some important questions here:

• How can the damage from another incident like this be reduced or prevented?
• How large (huge!) were the waves that did this? How often do they occur?
• How important is the storm surge and tide levels, and exactly how do they combine with the waves?

Figure1. Peggy's Cove, showing the path of water and part of the damage. White arrows show the path taken by the waves and water flow. (1) Area where water entered valley. (2) Breakwater along path to harbour. (3) Garage damaged by waves. (4) Gift Shop with foundation eroded away. (5) Government wharf damaged by currents and water levels. (6) Peggy's Cove lighthouse. (7) Parking lot of restaurant partially flooded and boulders moved about.

Conclusions

Peggy's Cove has known such flooding incidents from time to time for at least a hundred years. It is reasonable to assume that similar or stronger events will happen again in the foreseeable future. The behavior of these waves and events should be better understood in order that the most effective preventative measures be put in place.

This may be the most unusual damage incident caused by Hurricane Juan.

Figure 2: Garage damaged by a 4-5 foot wall of water.

Figure 3: Breakwater wall, looking downhill to the east.

Figure 4: Looking west from breakwater wall towards the harbour. Note the grass matted down towards the houses. The pool in the foreground is salt water from the waves breaking over the breakwater. The driveway to the left of the yellow house was destroyed. The gift shop to the right of the yellow house was damaged. The yellow house, itself, sustained little damage.