MONITORING PLANIMETRIC AND VOLUMETRIC CHANGES ON ACTIVE SAND DUNES

Sand dunes represent a natural physical ‘recording’ of how surface winds have moved sand deposits. However, complex dune shape can often complicate the interpretation of this sand movement record. Here we describe a technique for monitoring such dune position and shape changes without the necessity of obtaining expensive repeat coverage by airborne LiDAR data. We used differentially corrected global positioning system (DGPS) data to document the precise location of the crest and base of an active reversing sand dune at Great Sand Dunes National Park and Preserve in central Colorado, but the procedure we employed should be applicable to the study of any active sand dune. A Trimble GeoXH with postprocess differential correction provided three-dimensional positional data to better than 20 cm, sufficient to record the shape of the dune in detail. When imported into ArcGIS, the surveyed points were combined using a triangulated irregular network that captured the overall shape and location of the dune. These data could then be compared to an earlier LiDAR digital elevation model of the park, from which we could assess how the sand dune shape and location changed during the time between the two surveys. We intend to continue to monitor this same dune, along with other nearby dune forms, to evaluate the timescale over which such changes can be effectively obtained under the wind conditions prevalent at the park. We are optimistic that the procedure we successfully employed can be applied to studies of sand dunes wherever precise DGPS surveys can be conducted.