Coastal Erosion Modeling and Forecasting

Tom Ravens

Tom has an ME, BE, and BA in Engineering Sciences and a Ph.D. in Civil and Environmental Engineering. He has been researching coastal processes in Arctic Alaska since 2007. He is currently a Professor of Civil Engineering and Associate Dean of Research in the UAA College of Engineering. For this project, he and his team will be developing coastal erosion and nearshore sediment transport models for the Stefansson Sound. Coastal erosion models will include machine learning (Gaussian Processes) models, semi-empirical models, and process-based models.

 

 

 

Michael Ulmgren

Michael has a BE and a MS in Civil Engineering from UAA. Michael is the prime developer of Arctic Xbeach, which is the process-based coastal erosion model that we are employing in this project. Michael is also supporting the semi-empirical modeling effort through the development of a one-line shoreline change model using GENESIS software.

 

Dana Brunswick

Dana has a BE and an MS in Civil Engineering from UAA. Dana is the lead on the semi-empirical modeling effort using the GENESIS shoreline change software.

 

What are we doing and why?

The U.S. Bureau of Ocean Energy Management (BOEM) requires information on sediment transport within Foggy Island Bay and how sediment transport within the Bay may change over the lifetime of Hilcorp Alaska’s Liberty Project. We are (a) gathering information on historic shoreline position and environmental conditions, (b) developing and calibrating coastal erosion and sediment transport models with historic and contemporary data, and (c) projecting future conditions with the calibrated models. The nearshore sediment transport calculated will serve as the boundary condition of the regional sediment transport model used to determine how sediment transport conditions may change over the lifetime of the Liberty project.

How are we doing our work?

Building on the validated, process-based coastal erosion model for Drew Point Alaska (Ravens et al. 2012), we have developed a general-purpose, process-based, Arctic coastal erosion model (Ravens et al. 2017) based on the open-source coastal geomorphic change model, Xbeach (https://oss.deltares.nl/web/xbeach/). Xbeach is a state-of-the-art geomorphic change model which simulates the nearshore hydrodynamic (wave, current, water surface elevation) environment and the resulting sediment transport. It allows for a range of wave modeling approaches and a range of sediment transport formulations.  On the basis of the sediment transport calculations, it computes geomorphic change (i.e., erosion or accretion). The team has added a heat transfer module determining the temperature and phase of the water and sediments (frozen or thawed), creating Arctic Xbeach. The conventional Xbeach model provides the potential geomorphic change. Arctic Xbeach only allows the potential change to be actualized if the sediment/soil is thawed. Example output from Arctic Xbeach is provided in Figure 1. The figure depicts the change in the beach and bluff profile at Barter Island (Alaska) due to a 1-yr storm based on the conventional Xbeach model and based on Arctic Xbeach, labeled “No Permafrost” and “Permafrost”, respectively. The simulation demonstrates the importance of properly accounting for coastal permafrost thaw in Arctic coastal erosion modeling.

Figure 1. Arctic Xbeach-based plot of pre-storm and post-storm beach and bluff profile, showing the importance of explicit accounting of permafrost thaw.

The Arctic Xbeach model described above focuses mainly on cross-shore sediment transport. In some cases, shoreline change results from both alongshore sediment transport and cross-shore sediment transport. In these cases, the two forms of transport are integrated using the “one-line” model (Ravens and Sitanggang 2007):

where y is the cross-shore position, t is time, D is the depth of the active beach, Q is the alongshore sediment transport (readily calculated based on the nearshore wave environment), x is the alongshore position, and q_c is the contribution to shoreline change due to cross-shore sediment transport (from Arctic Xbeach).

For the BOEM project, beach profile and grain size data will be collected in the field portion of the project, and the Arctic coastal erosion model (including Arctic Xbeach and the Arctic one-line model) will be calibrated and validated using historic shoreline position data and available hydrodynamic and sediment transport data. In addition to providing hind-casts and forecasts of coastal erosion rates, the Arctic Xbeach model will provide data on the nearshore sediment transport processes associated with coastal erosion and sediment resuspension. These data will be incorporated into the larger domain sediment transport model.

References

Ravens, T. M., and K. I. Sitanggang. 2007. Numerical modeling and analysis of shoreline change on Galveston Island. J. of Coastal Research, 23(3): 699-710.

Ravens, T. M., Jones B. M., Zhang, J., Arp, C. D., and J. A. Schmutz. 2012. Process-Based Coastal Erosion Modeling for Drew Point, North Slope, Alaska . J. of Waterway, Port, Coastal, and Ocean Engineering. 138(2): 122-130.

Ravens, T. M., Ulmgren, M., Wilber, M. Peng, J. and G. Hailu. 2017. Arctic-capable coastal geomorphic change modeling with application to Barter Island, Alaska. Published and presented at IEEE/MTS OCEAN 2017, Anchorage, Alaska Sept. 18-22.