Colliery dams safe during typical winter
To the Editor,
There has been much confusion about emergency measures and the water levels at the Colliery dams this winter. Residents have raised safety concerns during very typical winter weather after learning that the city was close to implementing emergency measures on Jan. 11.
The important thing to note is that it is only if the lower dam overtops that there is concern for dam failure and this would take a day or two to occur after overtopping begins. On Jan. 11 the water level that caused so much concern was 40 centimetres, which is 1.6 metres below the top of the dam.
When water levels reach 0.6m emergency measures begin. The city begins monitoring the levels more closely and prepares for the next step. At 0.9m residents are called to prepare for possible evacuation. At 1.2m, sirens sound and people are evacuated. This is still 0.8m below the top of the dam.
We were told that the highest water level recorded in the last 34 years was 0.9m, well below the dam crest. So I believe, with these facts in mind, our typical winter weather is very unlikely to cause overtopping of the dam this winter.