abstract
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The objective of this thesis was to undertake an uncertainty analysis on the outputs from a two-dimensional hydrodynamic model. The analysis utilized an application of the Resource Management Associates' RMA2 model for the Upper St. Lawrence River in Ontario, Canada. Two uncertainty analysis methods, First-Order Second Moment (FOSM) and Monte Carlo analysis, are applied to calculate the uncertainty in water levels and velocities computed by the model.
Both uncertainty analysis methods can be applied together with two-dimensional hydrodynamic modelling, but based on the findings of this work, the FOSM method is preferred. First, FOSM estimates of uncertainty are slightly larger than those obtained using Monte Carlo analysis. Thus, FOSM provides a conservative estimate of the uncertainty, a positive characteristic. Second, the FOSM method is simpler to apply than Monte Carlo analysis, requiring less information to describe the model inputs, fewer model executions and computations to calculate the uncertainty. Third, FOSM provides an immediate indication of the primary contributors to the uncertainty in the output, where Monte Carlo analysis requires additional effort to do the same.
The model input that contributed the most to the uncertainty in the model outputs is the bottom resistance represented in RMA2 using Manning's n. The uncertainty in Manning's n is large and the model is sensitive to the parameter. As a result, a significant amount of uncertainty in the model outputs is contributed by this parameter.
Uncertainty analysis is a practical addition to the two-dimensional hydrodynamic modelling process. The effort required to complete an uncertainty analysis using the FOSM method is minimal and the resulting insight is meaningful. It provides information to the model developer, quantifying how good the model actually is. It also provides a measure of the accuracy of the model for future model users or clients using hydrodynamic modelling outputs.