General Notes on Graphs and Tables
In order to show a true comparison of the water levels that would result from the different regulation plans, each graph or table uses a standard set of water supply conditions. In some cases these are the recorded water supplies. In other cases, a "stochastic supply sequence" that has been statistically generated from recorded supplies to test plan performance with a wider range of supplies.
The current approach to regulation includes Plan 1958-D along with frequent deviations from the flows indicated by this plan. These deviations have depended on Board members' judgment, which has changed over time as the Board has gained more experience with regulation. To allow for true comparisons using different water supply conditions, a model called Plan 1958-DD has been developed that incorporates Plan 1958-D and the general practices followed by the Board when deviating from plan flows. Water levels shown for Plan 1958-DD in the graphs and tables for the 1900-2000 period are not actual recorded water levels, but rather simulations. Water levels shown for Plan 1958-DD for the 2001-2011 period are the actual recorded levels.
The unregulated water levels shown in the graphs and tables are based on Plan E, which was developed by the International Lake Ontario-St. Lawrence River Study. Under Plan E, the dam would be operated to replicate the flows that would have occurred without the dam, except for operations during ice formation that would be impossible to model under natural conditions. The new regulation plan attempts to move more toward natural flow patterns while continuing to reduce the frequency and severity of the most extreme water levels that would have happened with no regulation. Unregulated flows and Plan 1958-DD are shown in the graphs and tables to show how Plan Bv7 balances these objectives.
The regulation plan influences still water levels, or the levels that would occur on the lake and river with no effects from wind or waves. All of the water level graphs and tables show the still water levels that the different regulation plans would produce. These results depend routing a defined set of water supplies through the physical system. So while future water supplies are uncertain, the levels that would result from a particular set of water supplies have a high degree of certainty. The analysis based on economic and environmental performance indicators includes additional information, such as the probability that a storms will occur and the economic value of resulting impacts. This provides a more complete picture of the types of risk associated with the different plans, but introduces greater uncertainty.