The construction of the proposed hydro-electric generating station at the Bala Falls would require completely blocking-off the Bala north channel with a cofferdam. The proponent has stated this would be for the months of June through February. During these nine months all the flow through Bala could only pass through the Bala south channel, which has a maximum capacity of 252 m³/s.
The graph below (click on it for a larger view) shows the span of dates each year during which the flow through Bala was more than 252 m³/s. Therefore on the highlighted dates below, flow through the Bala north channel was needed to avoid flooding Lake Muskoka.
As expected, during spring freshet the Bala north channel is almost always needed. But what is important is that during the months of June through February (inclusive), flow through the Bala north channel was needed in 10 of the 45 years to avoid flooding Lake Muskoka.
That is, the proponent’s construction plans would create a (10/45=) 22.5% chance of flooding Lake Muskoka.
This is more than a 1 in 5 chance of flooding, which is far too risky (a 1 in 50 chance would be better design practice). We have therefore sent this letter to the MNR.