Techniques for GIS modeling of coastal dunes

Abstract

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.

A review of field methods to survey coastal dunes—experience based on research from South Baltic coast

“…The newest digital devices are suitable for obtaining accurate surface data. The GPS RTK is also suitable for point data collection (Andrews et al 2002). Those devices need to operate in real coordinate systems.…”

“…The surface measurements are usable for 3D digital terrain model (DTM) construction of coastal areas. The accuracy of such a model varies due to the digital computation techniques used in special software such as Surfer or ArcView (Andrews et al 2002;Montreuil et al 2013b). This subject will be analysed in another article.…”

“…Among them are levellers and theodolites. Surface measurements performed by means of conventional methods still provide information about topographic and volumetric changes of dune areas that can then be used for 2D and 3D mapping (Andrews et al 2002). Fig.…”

“…Measurement during dusk or night needs to be done with artificial light, which can illuminate the scale on the pole. This traditional method of beach and dune monitoring through profiles perpendicular to the shoreline has low accuracy because there are areas between profiles that are impossible to record (Andrews et al 2002). However, optical leveling of foredunes and other sandy coastal forms is a fast and easy method.…”

“…The field investigation methods may be divided as conventional survey using optical or laser equipment (Delgado and Lloyd 2004;Krause 2004;Andrade and Ferreira 2006;Khalil 2007) and digital GPS receivers reporting proper position in connection with a network of satellites (Andrews et al 2002;Baptista et al 2008;Harley et al 2011;Jeong-Min et al 2013;Montreuil et al 2013a). …”