To the Editor,
Re: Flood signage should be reconsidered, Letters, June 10.
Spectacular flows in the Chase River usually come during a rain-on-snow event. We had two such events in 1996 and 1997. Ninety centimetres of snow fell in a week, followed by 15 centimetres of rain over three days, creating a flow of about 35 cubic metres per second in the Chase River.
At that rate, the water flows over the top of the lower dam. That can erode the vegetation away, then the soil and backfill. That exposes the lower concrete face of the dam, which is then unsupported. This is when the concrete can fail, either catastrophically or with a small crack. If the concrete fails all at once, the people in the floodplain are in dire straits. If it cracks, they would be OK, but they would have to evacuate.
Rain-on-snow events have happened with regular frequency in the past and we don’t know what the future holds. All we know is that the weather is likely to get more extreme.
All provinces have seen extreme weather and extreme flooding. If we were clever, we would learn from those events and take the prudent, risk-averse option and remove the dams. Instead the Colliery Dam Park Preservation Society has chosen to accept the risk of having 220,000 cubic metres of water over the heads of 1,800 people.
Perhaps the flood signage should stay in place.
Charles ThirkillNanaimo