Hithaishi Hewageegana

Hithaishi Hewageegana

PhD in Coastal Engineering

Numerical modeling of the influence of tides on beach morphodynamics

1 minute read

Published:

Presented AGU Fall Meeting. 2018, Washington D.C

Four Beach transect at Duck, North Carolina (two transects in the Northern end and two transects in the Southern end) are analyzed from 1995 till 2018. Observed cross-shore sandbar migration rates are fitted as a function of the sediment transport capacity at the peak of the sandbar. The sediment transport capacity parameter is calculated using a Bailard type energetics approach, where the suspended sediment transport is calculated by considering the 4th power of the velocity at the peak of the sandbar. The velocity over the sandbar is composed of the wave orbital velocities and mean currents. The found parameter can be used as a reasonable proxy to identify the sandbar migration rate and direction.

Three different numerical models will be used during my PhD to assess the predictive capability of sand bar migration for a given wave climate. The models vary from 1D phase- and depth-averaged (XBeach), quasi 2DV phase-averaged (XBeach quasi 2DV) and 3D phase resolving (Mike 3 WAVE-MORPH). The physical processes included in each model are different. The comparison will allow us to understand which processes should be retained in order to accurately model sand bar migration.

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Predicting sandbar migration using a phase resolving 3D numerical model

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Presented at AGU Fall Meeting 2020, San Francisco, CA

Sediment transport and morphology was sucessfully implemented into the 3D wave resolving model SWASH. Sediment transport fluxes are calculated, taking acceleration and velocity skewness into account. The sediment transport of the model was validated using flume data, and it was able to reproduce the bedload correctly. Using this new implementation, we can assess the ability to reproduce onshore sandbar migration observed in measurements. This work primarily focuses on data collected at the Field Research Facility in Duck, NC. The newly implemented sediment transport and morphology feature in SWASH provides a valuable tool that will be used to improve the parameterization of the velocity profile and wave-shape-related sediment transport in wave averaged models such as XBeach and COAWST.

A simplified method to predict onshore sandbar migration. The Duck, NC case

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Published:

Presented at Ocean Sciences meeting 2020, San Diego, CA

Successful modeling of sandbar behavior is challenging due to the complex hydrodynamics processes which drive sediment transport and morphological changes. Finely tuned wave-averaged models have been shown to have some predictive capabilities for single sandbar migration cases, but they have poor predictive skills when applied for other sandbar migration cases. Here we propose a simplified model for evaluating sandbar migration. Our model takes wave-averaged parameters as input, but computes non-wave-averaged sediment transport processes using a reconstructed wave signal. This method explicitly solves for the sediment transport due to wave acceleration skewness and velocity skewness, avoiding parameterizations usually implemented in phase-averaged models. This work focuses on data collected at the Field Research Facility in Duck, NC. The proposed method is capable of successfully modeling the bar evolution over multiple cases. The model is a useful tool for coastal managers and researchers to forecast sandbar migration under different hydrodynamic conditions.