In the wake of news of an Esquimalt backyard slipping into the Gorge Waterway, a University of Victoria geography professor is warning that others are at risk.
鈥淭here are thousands of houses out there in similar situations,鈥� said Ian Walker, a professor of geomorphology, the study of how landscapes change.
Walker emphasized that he is not familiar with the Gorge property and can only speak generally about forces at work on shorelines and bluff formations.
But he said anyone interested in how the soil under a home might respond to something like an earthquake or a severe El Ni帽o鈥檚 worth of rainfall can retrieve the information from the sa国际传媒 government.
鈥淚t鈥檚 kind of buyer beware,鈥� said Walker.
A house at 933 Mesher Pl. recently lost much of its backyard when it slipped into the Gorge Waterway after heavy rain. Around the same time, a smaller slide hit a home on Arbutus Road in Saanich鈥檚 Gordon Head.
Esquimalt municipal officials have said the Gorge homeowner is responsible for any repairs and costs associated with the landslide.
Insurance coverage for landslides is not typically available.
Walker said soil saturated after heavy rains will become heavier, and if it鈥檚 along a bluff or cliff, it can slump.
If the slope has been subject to heaving wave action, it can also be carved out and weakened further.
For example, seaside bluffs along Beacon Hill are losing 15 to 20 centimetres a year, he said. Anyone can do the arithmetic and figure out when the bluffs will meet Dallas Road.
Walker said it鈥檚 important to keep in mind that bluff and cliff erosion rarely happens gradually. More typically, it happens suddenly in large events such as slides.
鈥淲e don鈥檛 really monitor erosion well, unlike the way we monitor other things, like river flows or tidal levels,鈥� he said.
Walker said homeowners or potential buyers can prepare themselves by looking at maps detailing soil types in a particular area.
The sa国际传媒 Geological Survey has drawn up maps detailing soil types in much of the province, including Greater Victoria.
The maps are mostly drawn with earthquake hazards in mind, but can be used when considering the stability of soil in a building site.
Walker said soil that might react dramatically to the shaking of an earthquake can also be susceptible to other forces, such as flooding or bluff erosion. Maps showing soil liquefaction hazards are especially helpful.
鈥淚f you look at the map, you can see areas throughout Greater Victoria that are quite susceptible to soil failure,鈥� he said.
For detailed maps, go online to the Ministry of Energy Mines and Petroleum Resources website at and search for earthquake, hazards, map, Victoria.
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How to reduce unstable-soil hazard
Homeowners can mitigate some of the problems of building near cliff edges, even where soil is unstable, says a geotechnical engineer.
Richard Brimmell of Brimmell Engineering Ltd. in Victoria said many of Victoria鈥檚 unstable soil sites have already been built upon. Declaring them off-limits is not reasonable.
鈥淧eople like to build all over the place and that is where engineers come in,鈥� said Brimmell.
Although each property is different, general measures can be taken to strengthen a cliff edge, he said, including:
鈥� Installing retaining walls to hold soil in place.
鈥� Improving drainage; pipes that carry water away or drilling of wells to collect water in a column can help prevent an unstable water buildup in the soil.
鈥� Planting foliage. Trees have deep roots to add structural strength to a cliff edge. Low-lying plants can improve water run-off.
Since every building site is different, subject to a variety of forces, conditions and stresses, only a specific examination and analysis can determine what measure or measures will work best in a location, Brimmell said.
He added that slumps and slides like the recent one on the Gorge Waterway are relatively common.
鈥淪horeline situations, on the ocean like this, they fail.鈥�
