FINAL REPORT - International Joint Commission

FINAL REPORT
Validation
The Plan Formulation and Evaluation Group identified critical flaws in the calculation of these coastal
performance indicators. At the June 2004 workshop, several plans were presented with high lake levels
causing large increases in hydropower and other benefits, with very little or no increase in Lake Ontario
coastal damages. The analysis later revealed two errors: (1) The 101-year simulation was performed as
one century-long experiment rather than a series of 101 one-year experiments. Using the one-century
approach, a home that might be flooded five times in a century would only be flooded once (after which
mitigation removed it from the pool of vulnerable homes), thus resulting in greatly underestimated
damages. (2) Digital Elevation Model data for a few Lake Ontario and U.S. upper St. Lawrence River
counties need to be updated. Calculations for some properties were at lower than actual elevations,
resulting in the overestimation of damages for those counties. New surveys were taken and the results for
the base plan were deemed credible.
Sensitivity Analysis
The susceptibility of shore protection to overtopping damages is partly influenced by the estimate of the
design water level used in the calculation. In the Flood and Erosion Prediction System (FEPS) Model, the
design water levels are attributed on a county basis and are estimated based on risk determined from a
statistical analysis of the historical wave and surge conditions for a particular county (standard coastal
engineering practice). A sensitivity analysis revealed that the choice of design water levels for a county
can influence susceptibility to overtopping failures under a particular plan. The use of higher design water
level estimates for areas along the south shore of Lake Ontario, where shore protection costs are greatest,
tends to decrease overtopping failure. Applying higher design water levels can significantly reduce the
differences among plans under the shore protection maintenance performance indicator. If, in fact, most
existing shore protection structures exceed the Coastal work group estimates of height requirements for
surge in U.S. counties, then the differences among plans are less than FEPS estimates. However, experience
suggests that U.S. shore protection structures are sometimes under-designed and that many if not most of
the structures have lower top elevations than estimated in the FEPS modeling, so the differences among
plans are at least what FEPS estimates and possibly more. Further details of the validation and sensitivity
analysis for FEPS are discussed in the Coastal TWG summary in Annex 2 of this report.
Environmental
Validation
Where possible, the Environmental Technical Work Group conducted verification of performance indicator
results by developing detailed spreadsheet calculations that were intended to reproduce the Integrated
Ecological Response Model (IERM) output for a given performance indicator. For some of the more
complex sub-models, it was necessary to develop simplified spreadsheet calculations that could adequately
reproduce the relative performance indicator response when two regulation plans were compared.
Verification of the IERM sub-models was also achieved through an iterative process whereby the individual
Environmental Technical Work Group researchers reviewed model results and provided feedback after each
version of the IERM was released. Validation of the research on the individual environmental performance
indicators is described in each of the performance indicator fact sheets.
Sensitivity Analysis
The Plan Formulation and Evaluation Group changed the overall environmental index and used a subset
(the “priority performance indicators”) of the 32 performance indicators that measure the most significant
sector changes rather than the overall basin impact, none of which changed plan rankings. Plan B + clearly
outperforms the other plans based on the distinguishing performance indicators, while Plan D + is about
the same as Plan 1958-DD and Plan A + is worse.
82 Options for Managing Lake Ontario and St. Lawrence River Water Levels and Flows