The “Tooth of Time” falls is the first rapid in the Gorge, although many paddlers put in below the falls when running the Gorge. For the “Tooth of Time” falls, you would read the Shand Dam discharge to view flow data.
After the “Tooth of Time”, the Grand River merges with a tributary, the Irvine. So, Gorge flow for the remainder of the run is the sum of the Shand Dam discharge AND the flow from the Irvine.
In summer months, Irvine discharge is often extremely minimal – like 0.3 cms.
In the GRCA webpage, their “summary report” lists Gorge flow itself. (which, again, is the sum of Shand Discharge and Irvine input).
The Guelph Kayak club and many others (me!) run the Gorge all summer, with summer lowflow being 4.8 cms or so. It is a bumpy run at that level, but is worth the trip for those of us for whom the Gorge is the closest water.
If you have to drive to get to the Gorge, I would look for flows >= 15cms, unless you’re jonesing for some whitewater and don’t want to make the trip to the Gull or others rivers. With the Grand coming down slowly after the spring run-off at this point, the level likely won’t approach 15cms until there’s a good rainfall.