Coastal dunes present a unique problem to coastal scientists because of the dynamic nature of most coastal dune systems. Coastal dunes can change shape quickly and frequently due to storm-generated winds and waves. Prevailing winds can transport significant amounts of sand throughout the dune system. Topographic and volumetric changes in a 150×40 m site on the Outer Banks of North Carolina were assessed through a series of monthly field surveys conducted over a 1-year period from May 1997 to May 1998. This paper discusses the Geographic Information System (GIS) methodology used for data acquisition and analysis and presents one methodology developed to measure 3-D dune morphodynamics using a 2-D and 3-D GIS. It serves as a guide for other coastal researchers who may have limited surveying or GIS experience. Issues concerning sampling routine, data density and grid cell size are discussed. The methodology followed results in the production of a grid of interpolated elevation values that can be represented in a variety of ways, including as topographic maps, digital elevation models (DEM) or two-dimensional cross-sections of the dune system. The grid from the May 1998 survey is subtracted from the May 1997 grid to obtain elevation change information that in turn can be represented graphically. The results of the analysis show that volumetric change over the 1-year period was dominated by erosion along the seaward face of the dune. The monthly surveys show that this erosion was the result of two northeasters in January and February 1998. The loss of volume is partially compensated for by accumulation to the rear of the foredune ridge, primarily in locations where blowouts facilitate aeolian transport of sediment from the beach. The implication is that the dune system is eroding rapidly due to storm activity. It also suggests that there is a mechanism for offsetting some of the volumetric loss through aeolian transport into the dune system.

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Abstract:The results of field measurements conducted in a small (19Ð37 ha) agricultural watershed on the North Carolina coastal plain during the summer of 1996 are presented. The objective of the study was to develop a more complete understanding of basin response in the region with respect to stormflow generation and, in particular, to identify the processes that determine storm runoff and the conditions under which such processes occur. Twenty-four storm events were monitored, including two tropical storm systems and two hurricanes. The data demonstrate considerable spatial and temporal heterogeneity in runoff generation within the watershed. Surface flowpaths, in the form of Hortonian overland flow and saturation overland flow, were found to be the dominant runoff processes during the storm events measured. The hillslope flowpaths had the same response time as the basin streamflow, but significantly shorter time of rise and lag times. The importance of Hortonian flow in a basin with sandy, permeable soils, as well as the rapid stormflow response in a low-relief area with a humid climate, was contrary to expectations. This, coupled with the contingency of runoff response, suggests that it may be difficult to generalize about runoff generation mechanisms in broad terms, and that a synoptic approach may be more appropriate.

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The spatial variability of air flow through complex topography is an important, but not fully understood, component of dune development and dynamics. This study examines the spatial variability of the wind field in a linear blowout in coastal dunes at Jockey's Ridge State Park, on the Outer Banks of North Carolina. A spatial array of single‐height anemometers and wind vanes were placed within the blowout. Topography exerted a significant steering effect when onshore winds approached from directions within 50° of the blowout axis. Under those conditions wind flow in the blowout aligned to the axis regardless of approach angle, maximizing the potential for erosion and transport in the trough. In other locations aspect variations caused deflection both proportional and disproportional to changes in the approaching wind. When prevailing winds approached from directions more oblique than 50° to the blowout axis, topographic steering through the blowout trough was reduced and secondary flow generated by flow separation over the trough became more prominent. During those approach angles, wind directions and speeds within the upper blowout trough became erratic as vortices and turbulence dominated the flow, minimizing transport potential. The changing characteristics of airflow in the blowout relative to differing approach angles has implications on dune development and variations in transport potential under changing conditions. Copyright © 2013 John Wiley & Sons, Ltd.