Exploring Nearshore-Beach-Dune Interaction through a Coupled Modeling Framework

The interface between the land and sea is complex. During high energy conditions large waves and elevated water levels can cause severe beach and dune erosion, whereas recovery takes place during extended periods of calm. Recent advances in numerical modeling have improved our ability to accurately model both storm-induced coastal hazards (e.g., XBeach; Roelvink et al., 2009), aeolian sediment transport in supply limited conditions (de Vries et. al. 2014), and dune eco-morphodynamics (e.g., Coastal Dune Model; Duran and Moore, 2013). However, process based numerical models incorporating the co-evolution of the coastal zone due to both subaqueous and subaerial processes to our knowledge, do not exist; hindering accurate forecasts of seasonal- to decadal-scale coastal evolution. Addressing this community need, a recent international collaboration has initiated the development of the open-source coupled numerical model Windsurf. Under the Windsurf framework, the coupled system resolves the most important subtidal and supratidal physical and ecological processes during both calm accretive conditions and high energy erosive periods.

Here we present the coupled model’s ability to simulate short-term beach and dune building processes on daily to seasonal time scales. The welding of intertidal sandbars to the shoreline has long been recognized as an important mechanism for beach and dune building (e.g., Houser, 2009) as beaches are often supply limited. Field experiments on the Oregon coast indicate that discrete sandbar welding events can deliver as much as 20 m³/m of sand from the nearshore to the backshore via the intertidal, resulting in shoreline progradation, backshore aggradation, and dune growth. Here we compare these field observations to model simulations demonstrating Windsurf’s ability to simulate beach-dune exchanges in supply limited scenarios.