The City released its first report on the test bores along the route of the proposed LRT through the downtown of Ottawa (DOTT). There was a lot of confusing fuss over the Campus Station (is there too much rock or not enough? will the tunnel there be bored or cut-and-cover? why would a open-to-the-surface slope into the tunnel cost about the same as a tunnel itself?) and not enough answers.

There was also some fuss about the existence of fault lines crossing the DOTT route. Unfortunately, no one seemed to have the time to call an expert or even a geology professor at a local university.

I was shocked … SHOCKED … to realize my recollections of Ottawa geology dated back forty years to university engineering, geology, and geography courses. Could it really be that long ago? For those with skimpy geologic awareness, Ottawa bedrock is largely limestone. Much of Ottawa used to be underwater or under glaciers, so the earth rebounded upwards, leaving cracks (fault lines) in the rock. All those downtown high rises are built on fault lines. So are the Fed parliament buildings. And the Queensway. And Heron Road bridge over the Rideau actually has its supporting columns straddling the fault lines. Does that make you feel more comfy and less worried about building a transit tunnel through downtown rock?

If you take the transitway today, you cross over fault lines. Here is the biggest one visible on the surface:

The same geologic feature can be seen whilst driving along the Ottawa River Commuter Expressway between Sliddel Street and Parkdale exit (lots of fossils here too). And from the Queensway just east of Parkdale exit, below the bowling lawn club on the south side. (The province planned to cover this fault line evidence with a concrete retaining wall but were discouraged by geology buffs who argued for the educational value of visible geology). Breezehill Avenue follows the crest of the uplift; Preston follows the bottom of the downshift, and Plouffe Park is the lowest point between the Glebe and the Ottawa River.

Geology played a role in the great fire of 1900. Dow’s Lake is actually held in place by a dam (Queen Elizabeth driveway runs along the top of Colonel By’s dam) and everything runs downhill from there. The great fire was extinguished by breaching the dam and flooding the area from Dow’s Lake to Plant Pool. Now, back to geology …