GBA 2021 - Spring Update

6 www.georgianbay.ca GBA UPDATE Spring 2021 9. Calculating the total amount of water that enters and leaves the Great Lakes system, called the net basin supply (NBS), is important for predicting water levels. The two different methods of calculating net basin supply (NBS) are not in conflict, but simply calculate NBS in two different ways for different purposes. The components method calculates the NBS as precipitation over the lake, plus runoff from the basin, minus evaporation. The residuals method calculates NBS as the water volume caused by the month-over-month lake level change, less the flows in, plus the flows out. Residual NBS works well in the development of regulation plans but is incapable of being used for the simulation of climate impacts on water levels, which use the components method. In the symposium the Large Lake Statistical Water Balance Model (LLSWBM) was discussed. LLSWBM reconciles discrepancies between the model and measurement-based estimates for these two different methods. 10. The tools we currently have to mitigate extreme high and low water levels are very limited. Adaptive management techniques/practice can only provide a partial offset to extreme water level impacts. Since more extreme levels are predicted to occur more often, we should examine implementing additional tools and solutions. It is likely that such tools will require major investments, but the cost of such investments will almost certainly be much lower than the total costs to governments, businesses, and residents of doing nothing and suffering the full impacts of extreme high and low levels in the future. GBA will be taking action on all the above items. The synopsis of the event, which contains more details of specific action items and the full list of questions and answers can be found at: georgianbay.ca/water/water-levels/water-levels- symposium-2020/ N o matter how long you’ve been on the Bay, the last few years have shown us dramatic lows and extremely high highs when it comes to water levels. In 2012/13 the water was so low that many of us worried about being able to dock our boats. Some docks were so out of the water that boaters had to moor where they could and then wade ashore. Docks stood high and dry like long-legged centipedes standing sentinel on the shores. We all got behind the Stop the Drop campaign and hoped and prayed that we would see the return of the waters. And then the water came back! Not so much in increments, but more like a flood. And it kept coming. Shores and shoals that we were used to seeing for a long number of years disappeared, seemingly overnight. We are now at record or near-record highs and are experiencing what too much water looks like. As you’ve read or are about to read in this issue of UPDATE , we were so concerned with rising water levels that we held a water symposium back in October, along with Georgian Bay Forever. The panel of acknowledged academics and institutional experts provided information and answered questions about how we could better manage water levels on Georgian Bay and across the Great Lakes. You can read about those recommendations in our Water Levels cover story. The purpose of this note is to share with you what we’ve all witnessed over the last number of years – the ebb and flow of our Georgian Bay waters. The photos below, from our Georgian Bay island in Cognashene, highlight how the water levels have fluctuated over the years from their lowest lows to their highest highs. Water levels on Georgian Bay affect us all in myriad ways. That’s why GBA will continue to look at those impacts and how to adapt to them at our next symposium. Continued from page 5 Lows Highs Photos: Rolfe Jones By Rolfe Jones