Cumberland's dams could liquefy in an earthquake
$1 million needed for upgrades

Marcel Tetrault
Comox Valley Echo

Tuesday, March 23, 2010

Two of the 100-year-old dams that store Cumberland's potable water supply could liquefy in an earthquake.

According to a report from the village's engineer, the bottom few metres of the Stevens Lake and Cumberland Lake No. 2 dams are "loose and saturated" and have a "high potential" of liquefaction if there is a 7.5-magnitude earthquake that lasts at least 25 seconds.

If the bottom portion of either dam fails, the result would likely be that the dam would spread horizontally before failing, either partially or completely.

Coun. Bronco Moncrief said that it was as far back as 2003, when the Hamilton Lake Dam breached, that recommendations to improve the dams were first put forward.

"Nothing has been done, and it's scary," said Moncrief. "If we don't get off our butts and get our water system straightened out, (it will be) just what we've dealt with (development) application after application they're just going to get tired and say what's the use, we don't have water so we're out of luck."

Several large and small developments have been floated in the village but none can yet proceed due to a 2007 moratorium on new water connections. The moratorium was put in place because the village's water supply system is at capacity.

On Monday the request of a local developer for an exception to the moratorium so he could build 30 affordable bachelor units was refused.

Should the dams liquefy and fail, water would be sent careening down to lower elevation lakes before winding up in the village's canal system and then pouring in to the former Chinatown settlement. No houses are in the path.

But something similar to that scenario did occur in the summer of 2008, when two young fishermen removed several planks from the Stevens Lake Dam in order to fill up a lower elevation fishing hole.

Instead the water poured into Perseverance Creek, killing dozens of salmon sheltering over the summer in small pools.

Both of the suspect dams are made of a timber crib/earthfill structure and were constructed some time between 1890 and 1930. Both are believed to have been built out of sandy glacial till.

Council decided on Monday that each dam would be reconstructed, at a total cost of $900,000.

In addition the Henderson Lake Dam, which was found to be generally resistant to liquefaction, is to be raised and widened to meet guidelines, at a cost of $45,000.

"This is one of the reasons I've been supporting some development around here, to get this amenity money so we could put it to use and get going," said Moncrief.

"We're going backwards right now. As soon as we can get the bucks together, lets get started on it."

The village's other dam, the Allan Lake Dam, was not inspected this time but the previous dam safety inspection found it to be in reasonable condition.

© Comox Valley Echo 2010