Land–sea interaction and morphogenesis of coastal foredunes — A modeling case study from the southern Baltic Sea coast
Introduction
Dunes are a common morphological feature in many coastal and arid environments. The basic factors involved in the formation of a dune are a certain amount of movable sediment on the surface, a flow (of e.g., water or air) acting on the bed surface which is strong enough to transport the sediment and an obstacle or perturbation which triggers a settling of the moving sediment. However, although the mechanism for the formation of a dune is clear, combinations of different flow strength and directions, sediment properties (e.g., grain size and composition), constraints of local topography and boundary conditions (e.g., source supply) can lead to quite different and complex dune patterns (Werner, 1999, Kocurek and Ewing, 2005). The interplay among aeolian transport, vegetation cover and hydrodynamic forces (e.g., storms) makes the morphological development of coastal dunes even more variable compared to dunes in an arid environment (e.g., desert) and imposes challenges to researchers for a comprehensive study of the dune morphogenesis (Hesp, 2002).
Among various dune patterns developed at the backshore, foredunes are most vulnerable as they stand at the foremost seaward line on the edge of the backshore, persistently reshaped by hydrodynamic and aerodynamic forces. Foredunes are able to develop where winds are effective in moving sediment onshore and a trapping of the moving sediment by a line of shore-parallel obstacles exists. This trapping of sediment is usually caused by vegetation (e.g., pioneer grasses and shrubs). Foredunes can range from relatively flat terraces to markedly convex ridges (Hesp, 2002) due to a variation of the driving wind spectrum, the sediment supply, the vegetation coverage and the growth rate. On a longer time scale their morphology is affected by climate change such like sea level oscillations (Tamura, 2012). Morphological development of a coastal foredune can be generally divided into three phases: incipient (or embryo) period, established period, and relict period (Hesp, 2002). However, as there are many environmental factors (e.g., wind strength and direction, storm frequency, beach width and migration, vegetation growth, sea level change) involved in the evolution of foredunes, some natural coastal foredunes may not go through all these three phases. For example, the foredune plains developed on a barrier coast (Swina Gate) at the southern Baltic Sea (as shown in Fig. 1) are characterized by well-preserved established sequences with a relatively stable accretion rate during the last several millenniums (Reimann et al., 2011).
Foredune dynamics is investigated usually within a framework of beach–dune interaction (e.g., Psuty, 1988, Hesp, 2002, Saye et al., 2005, Ollerhead et al., 2012). Cycles of sediment exchange between the foredune system and the beach, and between the beach and the nearshore submarine zone are recognized in this framework, within which processes involved in the beach–dune interaction and foredune evolution are studied at a range of spatial and temporal scales. On a short-term scale characterized by a temporal scale of seconds to days and a spatial scale of tens of meters, considerable efforts and progress have been made by field experiment (e.g., Hesp, 1983, Arens, 1994, Davidson-Arnott et al., 2005, Bauer et al., 2009) and modeling (e.g., Kriebel and Dean, 1985, Arens et al., 1995, Bauer and Davidson-Arnott, 2003, Jackson et al., 2011) to improve the knowledge about mechanisms that control the morphological development of coastal dunes. For the medium-term (temporal scale of months to decades and spatial scale of hundreds to thousands of meters) and long-term (temporal scale of centuries to millennia and spatial scale of kilometers to tens of kilometers) morphological evolution of coastal dune fields most of the existing studies are conceptual and descriptive (e.g., Hesp, 1988, Hesp, 2002, Sherman and Bauer, 1993, Orford et al., 2000, Aagaard et al., 2007, Anthony et al., 2010, Reimann et al., 2011, Ollerhead et al., 2012, Tamura, 2012, de Vries et al., 2012). Only recently numerical modeling became a tool for investigation of medium-to-long term coastal dune morphogenesis (e.g., Baas, 2002, Nield and Baas, 2008, Luna et al., 2011). Morphogenesis of some coastal dune types such as parabolic, nebkha and transgressive dunes has been studied numerically. However, there seems to be still a lack of a numerical model which is able to simulate a complete morphogenesis and evolution of coastal foredunes and foredune sequences on a medium-to-long term, probably due to the multi-scale characteristics of the physical and biological processes acting on a beach system and technical challenges in accurately describing the morphological response of the system to these processes.
In fact, although a coastal system is composed of two parts, i.e., subaqueous and subaerial, little effort has been done to combine these two parts into one integrated numerical model. Existing modeling studies on medium-to-long term coastal morphological evolution may underestimate the contribution of the subaerial coastal part to the whole system, especially the role of fordunes played in the transition between land and sea (Zhang et al., 2012). Thus, the main target of this study is to develop an integral model that is able to resolve the morphogenesis of coastal dune fields (especially the foredunes) on a medium-to-long term scale and on the other hand provide a reasonable estimate of the sediment budget for the subaqueous zone of the beach system.
The rest of the paper is organized as follows. After a brief explanation of the modeling principles on medium-to-long term coastal dune morphogenesis, details of a cellular automata approach for resolving subaerial processes, a process-based model for calculating alongshore and cross-shore subaqueous sediment budget and the coupling of these two models are described in Section 2. Application of this integrated model to a 1 km-long coastal section in the southern Baltic Sea is presented in Section 3. Discussion of the model with respect to its potentials as well as its shortcomings is given in Section 4, followed by conclusions in Section 5.
Section snippets
The model
Numerical models for aeolian sediment transport fall into two categories: (1) conventional models based on the approximation of Navier–Stokes equations to solve the aerodynamics and the resulting sediment transport on the dune surface (e.g., Jackson and Hunt, 1975, Weng et al., 1991, Van Boxel et al., 1999, Van Dijk et al., 1999, Herrmann et al., 2005, Luna et al., 2011); and (2) probabilistic models such as cellular automata (e.g., Werner, 1995, Baas, 2002, Zhang et al., 2010). Although the
Model application and result analysis
The integrated model is applied to a 1 km-long section of a barrier coast (Swina Gate, see Fig. 1) in the southern Baltic Sea for a 61-year (1951–2012) hindcast of its foredune development. The reason for choosing this particular coastal section for a numerical study is that: (1) this section represents a naturally accretionary coast characterized by well-preserved established foredune ridges (Fig. 1). It is more than 5 km away from an artificial pier (constructed in the 18th century) at the
Discussion
Development of a model fulfilling two basic requirements: (1) affordable computational expenses and (2) capture of the external key driving mechanisms and the internal nonlinear responses of the system, is a pre-requisite for reliable numerical studies (Zhang et al., 2013). These requirements serve as a base for the principles we follow in constructing an integrated model for investigation of medium-to-long term coastal foredune morphogenesis. Although the subaerial model is based on a cellular
Conclusions
Three major conclusions are drawn from the study. First, a successful application of the integrated model to the southern Baltic coast demonstrates the robustness and potential of a coupling between cellular automata approach and process-based profile-resolving models for a practical study of medium-to-long term coastal foredune morphology. Simulation results indicate that the morphogenesis of coastal foredunes is a result from a competition among wind-wave impacts, external sediment supply and
Acknowledgments
The historical wind and precipitation data (1951–2012) of the southern Baltic Sea were kindly provided by Dr. R. Weisse from Helmholtz-Zentrum Geesthacht, Germany. The simulations were carried out at MPI-IPP (Max-Plank-Institute for Plasma Physics) in Greifswald and Garching, Germany. We thank the Polish Maritime Office (Szczecin) for providing the valuable source data of high-resolution DEM and annual profile measurement from 2005 to 2012. Constructive comments from two anonymous reviewers and
References (66)
- et al.
Environmental controls on coastal dune formation: Skallingen Spit, Denmark
Geomorphology
(2007) - et al.
Shoreface sand supply and mid- to late-Holocene aeolian dune formation on the storm-dominated macrotidal coast of the southern North Sea
Mar. Geol.
(2010) Chaos, fractals and self-organization in coastal geomorphology: simulating dune landscapes in vegetated environments
Geomorphology
(2002)- et al.
A general framework for modelling sediment supply to coastal dunes including wind angle, beach geometry and fetch effects
Geomorphology
(2003) - et al.
Aeolian sediment transport on a beach: surface moisture, wind fetch, and mean transport
Geomorphology
(2009) - et al.
The effect of wind gusts, moisture content and fetch length on sand transport on a beach
Geomorphology
(2005) - et al.
Dune behavior and aeolian transport on decadal timescales
Coast. Eng.
(2012) Meso-scale modelling of aeolian sediment input to coastal dunes
Geomorphology
(2011)- et al.
A numerical approach for approximating the historical morphology of wave-dominated coasts — a case study of the Pomeranian Bight, southern Baltic Sea
Geomorphology
(2014) - et al.
The blown sand flux over a sandy surface: a wind tunnel investigation on the fetch effect
Geomorphology
(2004)
Cellular automata in geomorphology
Calculation of the separation streamlines of barchans and transverse dunes
Phys. A
Morphodynamics of incipient foredunes in N.S.W., Australia
Morphology, dynamics and internal stratification of some established foredunes in southeast Australia
Foredunes and blowouts: initiation, geomorphology and dynamics
Geomorphology
Aeolian dune field self-organization — implications for the formation of simple versus complex dune — field patterns
Geomorphology
Numerical simulation of time-dependent beach and dune erosion
Coast. Eng.
Present-day dune environment dynamics on the coast of the Swina Gate Sandbar (Polish West coast)
Estuar. Coast. Shelf Sci.
Prediction of cross-shore sediment transport at different spatial and temporal scales
Mar. Geol.
Reconstruction of Holocene coastal foredune progradation using luminescence dating — an example from the Świna barrier (southern Baltic Sea, NW Poland)
Geomorphology
Beach–dune morphological relationships and erosion/accretion: an investigation at five sites in England and Wales using LiDAR data
Geomorphology
Evaluation of 10 cross-shore sediment transport/morphological models
Coast. Eng.
Beach ridges and prograded beach deposits as palaeoenvironment records
Earth Sci. Rev.
A multi-scale hybrid long-term morphodynamic model for wave-dominated coasts
Geomorphology
A coupled modeling scheme for longshore sediment transport of wave-dominated coasts — a case study from the southern Baltic Sea
Coast. Eng.
Numerical models and intercomparisons of beach profile evolution
Coast. Eng.
Aeolian Processes in the Dutch Foredunes
Transport rates and volume changes in a coastal foredune on a Dutch Wadden island
J. Coast. Conserv.
Air flow over foredunes and implications for sand transport
Earth Surf. Process. Landf.
The Physics of Blown Sand and Desert Dunes
Surf similarity
Modelling desert dune fields based on discrete dynamics
Discret. Dyn. Nat. Soc.
Validation and application of beach storm erosion models in Australia
Cited by (27)
Simulating surface soil moisture on sandy beaches
2023, Coastal EngineeringNumerical simulations of wave climate in the Baltic Sea: a review
2023, OceanologiaCitation Excerpt :Owing to a relatively mild wave climate in several semi-sheltered regions of the Baltic Sea and especially owing to difference in the periods of some types of vessel waves, long ship waves may serve as a fundamentally new forcing component and a source of substantial danger to some sections of sedimentary coasts (Soomere et al., 2003). Simulation of wave extremes is also often a part of the analysis of land-sea interaction and morphogenesis of coastal foredunes (Zhang et al., 2015). Properties of extreme wave fields determine several core parameters of beaches such as the closure depth and are thus the starting point of, e.g., express techniques for estimates of sand loss or gain in specific types of beaches (Kask et al., 2009; Soomere and Healy, 2011).
Coastal Dunes
2022, Treatise on GeomorphologyAirflow Dynamics Over Unvegetated and Vegetated Dunes
2022, Treatise on Geomorphology