Graduate Thesis Or Dissertation
 

A novel framework for uncertainty propagation in river systems based on performance graphs using two-dimensional hydrodynamic modeling

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/xd07gw80f

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  • This thesis presents a novel approach for propagation of uncertainty in river systems. Errors in data observations and predictions (e.g., stream inflows), in model parameters, and resulting from the discretization of continuous systems, all point to the need to accurately quantify the amount of uncertainty carried through the modeling process. In the proposed framework, stochastic processes are incorporated directly into the physical description of the system (e.g., river flow dynamics) with the goal of better modeling uncertainties (both aleatoric and epistemic) and hence, reducing the ranges of the confidence intervals on quantities of interest. We represent uncertainty in stream inflows via an error term modeled as a stochastic process. Stochastic collocation is then used to discretize random space. This non-intrusive approach is both more efficient than Monte-Carlo methods and is as flexible in its application. The flow dynamics are simulated efficiently using the performance graphs approach implemented in the OSU Rivers model. For one-dimensional unsteady flow routing, the performance graph (PG) approach has been shown to be accurate, numerically efficient, and robust. The Hydraulic Performance Graph (HPG) of a channel reach graphically summarizes the dynamic relation between the flow through and the stages at the ends of the reach under gradually varied flow (GVF) conditions, while the Volumetric Performance Graph (VPG) summarizes the corresponding storage. The hydraulic routing for the entire system consists of dividing the river system into reaches and pre-computing the hydraulics for each of these reaches independently using a steady flow model. Then, a non-linear system of equations is solved that is assembled based on information summarized in the systems' performance graphs, the reach-wise equation of conservation of mass, continuity and water stage compatibility conditions at the union of reaches (nodes), and the system boundary conditions. For complex flows in river systems such as when there is flow over floodplains, the dynamic relation between water stages and flow in a river reach is best represented by depth averaged two-dimensional hydrodynamic models. The applicability of two-dimensional flow modeling for the construction of PGs for unsteady flow routing in complex river networks is explored. To illustrate application of the uncertainty propagation framework and PGs derived from two-dimensional flow models, a test case is presented that examines uncertainty quantification and flood routing through a complex section of the Fraser River in British Columbia.
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