City puts dams and evacuation warning system to tests
The City of Nanaimo was busy testing its new evacuation warning system last week and the structural integrity of the Colliery dams.
The evacuation warning system was put through its paces Wednesday, starting at about 10:20 a.m. when the city activated its telephone call alert system. The system links to households in Harewood that would be in the flood region should the dams at Colliery Park fail due to an extreme weather or seismic event and alerts residents to run for high ground.
“It phoned people in the inundation zone below Colliery dams and advised them that we were running a test,” said Karen Lindsay, Nanaimo emergency services coordinator. “It also sent an e-mail to people if they chose that option of communication.”
The call-out system is backed up by an audible warning system, which verbally announces the nature of the emergency, followed by a three-minute wailing tone similar to the sound of an air raid siren.
The $60,000 system, located in the John Barsby Secondary School grounds, projects the warning from two banks of three horn-loaded speakers arrayed so the warning siren can be heard over a 1.6-kilometre radius covering the flood inundation area.
The full-volume test is what people would hear in the event the dams were likely to fail.
The system can be activated manually on site or remotely and will be tested monthly.
“The difference between this test and the monthly tests that are going to occur, is that the monthly tests are going to be a 30-second, 50-per cent volume test and that’s just for us to make sure all of our programs are working and the mechanics and the procedures we set up are working,” Lindsay said. “We wanted do this three-minute test to ensure that everything we put in place was working and functional.”
John Barsby Secondary School, which is in the inundation zone, took the opportunity to practise a full evacuation.
Following the warning siren, hundreds of students mustered in the school’s sports field where roll call was taken. In case of a real emergency the students would be rushed to a staging area on higher ground.
The siren warning system will be activated differently depending on the nature of the emergency – an extreme weather event versus a seismic event.
“In an extreme weather event we’re monitoring and looking at all the systems – monitoring the water levels and monitoring the dams,” Lindsay said. “There we have more time because we’re watching them and [the system] would be triggered by our dispatch.”
In a seismic event strong enough to cause the dams to fail, the city will trigger the system immediately, since current estimates indicate residents will only have about 10 to 12 minutes to safely evacuate the area.
How well the Colliery dams will fare under stress was also being explored last week when geotechnical engineering firm Golder Associates examined the two dams.
Geophysicists were on site Thursday surveying the interiors of the dams with ground-penetrating radar. The technology, one of several employed for the survey, was one of the non-invasive methods used to minimize disturbance to the structures.
The survey was carried out as part of the Colliery Dams Technical Committee’s mandate to determine the best methods to mitigate the risk of dam failure.
The technical committee is made up of representatives from the city, Snuneymuxw First Nation, Colliery Dams Park Preservation Society and Golder.
A second phase of the site investigation, involving actual drilling into the embankments and concrete cores of the dams, will likely take place in early February.