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Two-Layer and Two-Phase Modeling of Shallow Flows with Dam-Break and Swash Zone Applications


Coastal areas are important habitats and contain large human populations. It is estimated that 20 million people reside along coasts below normal high tide levels and over 200 million people are vulnerable to coastal flooding during storms. Many communities are currently protected from flooding by beaches that are sometimes modified with anthropogenic (artificial) berms, so understanding and characterizing beach and berm response to storm waves is critical to adapting and mitigating climate change effects. Beach dynamics are challenging to model because of the complexity of wave dynamics, sediment transport and bed profile adjustments.

This dissertation aims to advance the state of the art in coastal flood prediction by improving modeling of beach dynamics over times scales of hours, when a combination of high tides, storm surge and waves from a storm event can threaten flooding. It is envisioned that with advances in laser scanning technology, beach profiles can be rapidly assessed to provide initial conditions to swash zone models, but improvements in mechanistic modeling are needed to predict whether a beach will be eroded and overtopped, and the extent of flooding, especially when anthropogenic beach berms are used to strengthen coastal flood defenses.

This dissertation proposes a beach model based on vertically averaged, multi-phase flow equations solved by a shock-capturing finite volume scheme. The model domain corresponds to the the so-called swash zone, the region between the shoreline and the inner surf zone where a layer-averaged model based on the assumption of hydrostatic pressure has been found to be a good approximation of system dynamics. Further offshore at intermediate to deep water depths, spectral wave models are routinely applied to describe wave transformations and output can be used as a boundary condition for the beach model.

The main contributions of this dissertation include new shock-capturing numerical methods for solving layer-averaged multi-phase flow equations, original experiments characterizing anthropogenic berm erosion and overtopping at field scale, and numerical modeling of beach and berm erosion aimed at measuring the predictive skill of the proposed model, developing an improved process understanding, and assessing strengths and weaknesses of the model.

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