Could not be built safely in the time available, risking flooding and destruction

The proponent’s current Alternative 1A proposal would obstruct so much of the north channel during construction that there would be an unacceptable risk of flooding Lake Muskoka, damaging property, and washing-out the highway bridge. The proponent should be required to provide an analysis of this risk, as they did for their previous Option 2 proposal.

Detail
The maximum flow capacity of the south channel is 252 m³/s and the capacity of the north channel is 218 m³/s. To build the intake for the proposed Alternative 1A generating station, approximately 85% of the cross-sectional area of the north channel would need to be obstructed by a temporary cofferdam. So during much of the construction period, the flow capacity through Bala would be closer to 252 + (0.15 x 218) = 285 m³/s.

Using Moon River flow data from 1965 through 2009, the histogram below shows how many days for each week of the year that the flow exceeded 285 m³/s (for flooding calculations, we cannot assume the Burgess Creek generating station would be passing its usual 4 m³/s of flow).

As you can see, there is only a 15-week period after the spring freshet when it could be assured that the proposed construction obstruction would not cause flooding of Lake Muskoka. Such high water could not only damage docks and boat houses on Lake Muskoka, it could wash out the highway bridge over the north channel and damage the dams as well.

Of course, much more analysis of this data could be done. For example, to show the liklihood that such high-flow events would be of long-enough duration to cause flooding, and also to ensure that the flow through Bala would not just be adequate for the historical data, but would be able to pass the worst storm expected in at least 100 years, as Ministry of Natural Resources typically requires for such high-risk projects.

The proponent provided such an analysis for their previous Option 2 proposal, but has not done so for their current Alternative 1A proposal even though it would; block more of the north channel, for a longer duration, and with much worse consequences if a high flow event occurred.