Coastal landscape change represents aggregated sediment transport gradients from spatially and temporally variable marine and aeolian forces. Numerous tools exist that independently simulate subaqueous and subaerial coastal profile change in response to these physical forces on a range of time scales. In this capacity, coastal foredunes have been treated primarily as wind-driven features. However, there are several marine controls on coastal foredune growth, such as sediment supply and moisture effects on aeolian processes. To improve understanding of interactions across the land-sea interface, here the development of the new Windsurf-coupled numerical modeling framework is presented. Windsurf couples standalone subaqueous and subaerial coastal change models to simulate the co-evolution of the coastal zone in response to both marine and aeolian processes. Windsurf is applied to a progradational, dissipative coastal system inWashington, USA, demonstrating the ability of the model framework to simulate sediment exchanges between the nearshore, beach, and dune for a one-year period. Windsurf simulations generally reproduce observed cycles of seasonal beach progradation and retreat, as well as dune growth, with reasonable skill. Exploratory model simulations are used to further explore the implications of environmental forcing variability on annual-scale coastal profile evolution. The findings of this work support the hypothesis that there are both direct and indirect oceanographic and meteorological controls on coastal foredune progradation, with this new modeling tool providing a new means of exploring complex morphodynamic feedback mechanisms.@en

Due to the wide range of complex processes in the active coastal zone, individual studies have tended to focus on specific time scales (e.g., event-scale erosion) and/or specific morphological units, (e.g., the nearshore bar zone). As a result, the wet and dry portions of the beach have typically been studied independently. In nature, however, the nearshore and the backshore are highly interdependent and understanding the linkages between these units is critical to characterizing coastal evolution. For example, during periods of intense storm conditions (e.g., major El Niños on the U.S. West Coast), elevated water levels and large waves commonly lead to the scarping, or even destruction, of wind formed dunes. Given that dunes act as a form of green infrastructure and are a major asset to the coastal zone, it is critical to be able to forecast backshore evolution. Existing models for backshore recovery, however, are typically based on local historical trends rather than a mechanistic understanding including onshore sediment transport, dune growth, and the role of ecomorphodynamic feedbacks. Therefore, most likely as a result of the historical academic separation of wave and wind driven processes, geomorphology and ecology, and short- and long-term processes, our understanding of beach and dune building is still in its infancy. Here we describe SEDEX2, the Sandbar-aEolian-Dune EXchange Experiment, a comprehensive summer 2016 field campaign in which measurements of waves, currents, wind, dune ecology, subaqueous and aeolian sediment transport, and subsequent morphological changes were collected along the Long Beach Peninsula, WA. The data collected during the six-week experiment are contextualized by nearly two decades of focused research on the seasonal-centennial scale evolution of this rapidly prograding system. The findings of this study, actively bridging across disciplines, morphometric units, and temporal scales are informing conceptual and numerical models of beach-dune interaction and helping to improve management of vital backshore resources.@en

The Sand Motor is an artificial sandy peninsula extruding from the Dutch coast about 1 kilometer into the North Sea (Stive et al., 2013). It is virtually permanently exposed to tides, waves and wind and is consequently highly dynamic. In order to understand the complex morphological behavior of the Sand Motor, it is vital to take both subtidal and subaerial processes into account. About 70% of the Sand Motor area is located above 2m+MSL and is therefore uniquely shaped by subaerial processes. These dry areas are hardly eroded due to the presence of a coarse sand armor layer that was naturally established over time. However, significant aeolian transport is observed originating from the intertidal beaches surrounding the Sand Motor. Due to periodic flooding no armor layer can be established in the intertidal zone. Consequently, subtidal processes significantly influence the subaerial morphology. An international collaboration initiated the development of the open-source Windsurf modeling framework that enables us to simulate multi-fraction sediment transport due to subtidal and subaerial processes simultaneously. The Windsurf framework couples separate model cores for subtidal (XBeach; Roelvink, 2006) and subaerial morphodynamics (Coastal Dune Model; Duran and Moore, 2013) and multi-fraction aeolian sediment supply (AeoLiS; based on work by de Vries, 2015). Preliminary model results from a one-year one-dimensional simulation show a concentration of aeolian sediment supply from the intertidal beach area during calm conditions and an elevated aeolian activity shortly after a strong wind or surge event. The period of elevated transport may last for over a week resulting in the immediate initiation of recovery after a surge. Here we will present an application of the Windsurf modeling framework on the Sand Motor and a detailed description on how the interaction between subtidal and subaerial processes explain its complex morphological development. @en

Duran and Moore (2013) recently extended the model of Hermann et al. (2008) to create an aeolian eco-morphodynamic model (the Coastal Dune Model, CDM) to simulate the formation of coastal foredunes. De Vries et al. (2014) initiated development of a model to simulate the influence of supply-limiting factors on aeolian transport (now the AeoLiS model). Roelvink et al. (2009) developed a modelling approach to dune erosion, overwashing and breaching (XBeach), which connects the upper shoreface with dune systems during storms. Despite the importance of interactions that occur across the spatial domains and range of conditions represented by these process-based models, CDM and AeoLiS treat storm erosion in a schematized way and XBeach does not address inter-storm development of topography. Thus, we are collaborating to develop WindSurf, consisting of: (1) XBeach (2) CDM and (3) AeoLiS. In addressing both subaqueous and subaerial sediment transport and erosion during storms as well as inter-storm evolution of subaerial topography, the resulting coupled model will allow, for the first time, process-based simulation of event- and decadal-scale co-evolution of nearshore, beach and dune systems. @en

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. @en