Multiscale assessment of shoreline evolution in the US Pacific Northwest via a process-based model

Prediction of shoreline evolution in coastal environments is critical to aid adaptation strategy planning for coastal communities. To perform reliable predictions, process-based shoreline change models have recently gained popularity in many applications. The study region here, Tillamook County, Oregon, on the US Pacific Northwest coast, has recently been experiencing elevated shoreline erosion rates. The inherent uncertainties driving coastal change, e.g., sea-level rise and changing patterns of storminess, emphasize the need for robust shoreline evolution predictions in this region. To this end, we applied CoSMoS-COAST, an ensemble data-assimilated shoreline model that simulates short- and long-term shoreline change processes. We calibrated and validated the model using the hindcasted wave time series and observed shoreline positions and found a strong correlation between the number of observed shoreline positions and the model’s hindcasting skill. Moreover, results revealed an alongshore close-to-uniform shoreline change rate in the past several years, mainly driven by short-term, wave-driven processes. So far CoSMoS-COAST has performed satisfactorily with the spatially sparse supply of quality historical shoreline positions in our application. Moreover, this model resolves various components (e.g., short- and long-term processes) in the shoreline change sufficiently. This study represents a starting point in the long-term projection of shoreline evolution throughout the entire PNW (Oregon and Washington) coastline since Tillamook County features the majority of the coastal settings present in other coastal regions in the PNW.