As with most dune fields, the White Sands Dune Field in New Mexico forms in a wind regime that is not unimodal. In this study, dune behavior at White Sands was documented from a time series of five lidar-derived digital elevation models (DEM) and compared to a record of wind direction and speed during the same period. For the study period of June 2007 - June 2010, 244 sand-transporting wind events occurred and define a dominant wind mode from the SW and lesser modes from the NNW and SSE. Based upon difference maps and tracing of dune brinklines, overall dune behavior consists of migration to the NE, but with along-crest migration of dune sinuosity to the SE. Permutations of the DEMs allow matching specific dune behavior with wind modes. The SW winds are transverse to dune orientations and cause most forward migration. The NNW winds cause along-crest migration of dune sinuosity and low stoss bedforms, as well as SE migration of NE-trending dune terminations. The SSE winds cause ephemeral dune deformation, especially crestal slipface reversals. Dune deformation occurs because of unequal deposition along the lee face as a function of the incidence angle formed between the wind and the local brinkline orientation. Incidence-angle control on dune deformation and types of lee-face surface processes allows for an idealized model for White Sands dunes. The dunes behave as complex systems in which each wind event deforms the dune shape, this new shape then serves as the configuration for the next wind event. / text

Coastal foredunes are natural aeolian bedforms located landward of the backshore and which interact continuously with the beach. Traditionally, coastal dunes have been associated with onshore winds, however they can be found under more complex wind regimes where offshore winds are common such as the UK East coast, Northern Ireland and New Zealand. This research investigates the ways in which foredune-beach interactions occur under a complex wind regime at a range of overlapping temporal and spatial scales and is innovative in that it explicitly links small-scale processes and morphodynamic behaviour to large scale and long-term dynamics. The study area is the north Lincolnshire coast, East England. Detailed observations of airflow at three locations under varying wind regimes revealed considerable spatial variations in wind velocity and direction, however it was possible to determine a general model of how foredune topography deflected and modified airflow and the resultant geomorphological implications (i.e. erosion and deposition). During direct offshore and onshore winds, airflow remained attached and undeflected; and distinct zones of flow deceleration and acceleration could be identified. During oblique winds airflow was deflected to become more parallel to the dune crest. The field sites used are characterized by a seasonal erosion/accretion cycle and a series of increasingly complex models was developed and tested to determine whether it was possible to predict sand volume changes in the foredune-beach system based on a limited number of variables. The model predictions were tested against detailed digital terrain models at a seasonal timescale. The model prediction that best matched the observed (surveyed) sand volume changes included wind speed, direction, grain size, fetch effect controlled by beach inundation and angle of wind approach was accurate to within ±10% for 18 out of 48 tests at the seasonal scale and 6 out of 12 tests over periods of >5 years. A key variable influencing foredune-beach sand volume is the magnitude and frequency of storm surge events and this was not factored in to the model, but may explain the model-observation mismatch over the medium-term on two occasions. Over the past 120 years historical maps and aerial photographs indicate long-term foredune accretion of approximately 2 m year-1 at the three study sites (1891-2010). At this timescale, rates of coastal foredune accretion reflect the low occurrence of severe storm surges and suggest rapid post-storm recovery. The morphological response of the foredune-beach morphology is considered to be a combination of controlling and forcing factors. Process-responses within the system, associated with nearshore interactions and sediment transfer from the littoral drift, are compiled into a multi-scale morphodynamic model. Important to match appropriate dataset to scale of research question or management plan being explored. In the case of management, long-term records of past activity are necessary to predict the future but also to understand natural responses of system to short-term impact such as storm surge.