Abstract
In this study, we propose a new baseline and transect method, the open-source digital shoreline analysis system (ODSAS), which is specifically designed to deal with very irregular coastlines. We have compared the ODSAS results with those obtained using the digital shoreline analysis system (DSAS). Like DSAS, our proposed method uses a single baseline parallel to the shoreline and offers the user different smoothing and spacing options to generate the transects. Our method differs from DSAS in the way that the transects’ starting points and orientation are delineated by combining raster and vector objects. ODSAS uses SAGA GIS and R, which are both free open-source software programs. In this paper, we delineate the ODSAS workflow, apply it to ten study sites along the very irregular Galician coastline (NW Iberian Peninsula), and compare it with the one obtained using DSAS. We show how ODSAS produces similar values of coastline changes in terms of the most common indicators at the aggregated level (i.e., using all transects), but the values differ when compared at the transect-by-transect level. We argue herein that explicitly requesting the user to define a minimum resolution is important to reduce the subjectivity of the transect and baseline method.
Highlights
Diverse and complex natural processes continually change coasts in ways that are physical, chemical, and biological, at scales that range from microscopic to global
All open-source digital shoreline analysis system (ODSAS) results are within a factor of 1.2 to 0.7 when compared with the digital shoreline analysis system (DSAS) results, with the largest differences corresponding to A05 and A04
We argue here that while there is an unavoidable degree of subjectivity when using the baseline transect method to measure coastline change, this can be reduced by explicitly including the spatial resolution as part of the process (Figure 5), which is especially important when assessing very irregular coastlines [27]
Summary
Diverse and complex natural processes continually change coasts in ways that are physical, chemical, and biological, at scales that range from microscopic (grains of sand) to global (changes in sea level). Strictly defined as the intersection between water and land surfaces for practical purposes, the dynamic nature of this boundary and its dependence on the temporal and spatial scale at which it is being considered results in the use of a range of shoreline indicators [4]. The specific shoreline definition chosen is generally of lesser importance than the ability to quantify how a chosen shoreline indicator relates in a vertical/horizontal sense to the physical land–water boundary [4]. Regardless of the shoreline indicator acting as a proxy for the coastline, it is always represented as a vector polyline, which is a series of connected vertices that do not form an enclosed shape
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