Analyzing topographic change profiles in coastal foredune systems: Methodological recommendations

Abstract

Estimates of total sand volume in foredunes are commonly made for purposes of predicting coastal erosion and inundation potential during major storms, which is of critical importance for resource management and engineering purposes. However, changes in dune volume through time are potentially of greater relevance to process geomorphologists because volume changes are diagnostic of the long-term evolution of beach-dune systems and can be related to drivers of change (e.g., storm climatology, sediment supply, human action). The methods by which dune volume change estimates are made vary widely in the literature because there are no established protocols that provide guidance on the horizontal distances over which volume integration should be performed. In addition, identifying a diagnostic geomorphic feature such as the dune toe as a limit on integration is fraught with subjective uncertainties. In this paper, an objective methodology for quantifying dune volume change directly (rather than absolute volume) is proposed that is simple, intuitive, and robust. The horizontal limits of integration are identified by zero-crossings in the topographic change profiles between two transect surveys taken at different times, and this avoids challenges associated with identification of the dune toe as a fixed profile feature. Instead, the proposed method focuses on locations of morphodynamic significance where there has been a transition from erosion to accretion in the time interval between surveys.