PATTERNS OF MORPHOMETRIC PARAMETERS IN A LARGE BEDFORM FIELD: DEVELOPMENT AND APPLICATION OF A TOOL FOR AUTOMATED BEDFORM MORPHOMETRY

Abstract

Code that runs in the GRASS geographic information system (GIS) environment (available at www.grass.fbk.eu) has been developed to extract bedform morphometric parameters automatically from bathymetric digital elevation models. The code, r.dunes, uses a raster scanning approach, analogous to taking a series of closely spaced cross-sections. The processing pipeline may be summarised as follows: (1) rotation of bathymetric grid; (2) extraction of summit points; (3) extraction of a pair of trough points for each summit point; (4) calculation of dune parameters. The method of steepest descent is central to the extraction of the locations of the trough points where the latter are located with sub-pixel resolution. The code was applied to a digital terrain model of a large bedform field in the upper Bay of Fundy with distinctive two-dimensional bedforms and subject to maximum depth-averaged tidal currents of 2m·s -1 . Inspection of a length/height plot revealed three distinct clusters of continuous bedforms with measurements that corroborate a hierarchical dune growth model involving coalescence of two smaller dunes to form a single large dune. Inspection of the spatial distribution of observed bedform height relative to predicted height according to a globally observed height/length relationship indicates that peripherally located bedforms tend to be sediment starved while longer, or more centrally located, bedforms reach or exceed their predicted dimension, possibly because of the limited width of sediment pathways. The code is available for download at www.ria.ie/publications/journals/irish-journal-of-earth-sciences.aspx.