Date of Award:

2017

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Watershed Sciences

Advisor/Chair:

Patrick Belmont

Abstract

Predicting the frequency and aerial extent of flooding in river valleys is essential for infrastructure design, environmental management, and risk assessment. Such flooding occurs when the discharge of water within a river channel exceeds its maximum capacity and the extra water submerges the adjoining floodplain surface. The maximum capacity of a channel is controlled by its geometry, gradient, and frictional resistance. Conventional flood prediction methods rely on assumptions of unchanging flood probabilities and channel capacities. However, changes in climate, land cover, and water management have been shown to systematically shift the magnitude and variability of flood flows in many systems. Additionally, alluvial river channels continually adjust their geometries according to characteristics of flow and sediment regimes. For example, channels can expand their geometry during high-energy flows through erosion, then contract their geometry through sediment deposition during low-energy flows. This means that changes in flow magnitudes, frequencies, or durations can cause changes in a channel’s maximum capacity due to adjustments in river channel geometry. Therefore, future changes in river flow regimes and channel geometry may amplify or attenuate the frequency and magnitude of flood inundation in unexpected ways.

The focus of this thesis is the development of a novel simulation model to investigate potential changes in the frequency and aerial extent of floodplain inundation due to systematic changes in peak flows and subsequent adjustments in channel geometry and capacity. The model was run using six hypothetical flow scenarios to explore how changes in the mean and variance of an annual peak flow series influences the frequency and magnitude of floodplain inundation. In order to qualitatively simulate the various mechanisms controlling channel adjustment across a continuum of different river environments, each scenario was run multiple times while gradually varying model parameters controlling the amount of permissible adjustment in channel geometry. Results suggest that systematic shifts in peak flows cannot be translated directly to changes in the frequency or magnitude of floodplain inundation due to the non-linear factors controlling the rate and trajectory of channel adjustment. Insights gained from these results demonstrate the need to account for potential changes in both peak flows and channel capacities in the prediction and mitigation of flood hazards.

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