Testing the Red Relief Image Maps methodology to enhance the beachrock cartography in Torredembarra coast (Catalan coast, West Mediterranean Sea)

Beachrocks are cemented coastal deposits formed within the intertidal zone by the precipitation of magnesium-rich calcium carbonate. They constitute important paleogeographic and paleoclimatic markers, as they allow the reconstruction of past shoreline evolution. In addition, beachrocks influence current coastal dynamics and represent valuable geological heritage and ecological reservoirs that require preservation.

This study focuses on a sequence of multiple beachrock levels located along the Catalan Coast (NE Iberian Peninsula). The system consists of a complex sequence of submerged beachrocks with a wide formation range, situated at water depths between −0.25 m and −48 m below the current sea level. These deposits exhibit lateral continuity of up to 4.5 km and are characterized by reduced thicknesses and low geomorphic expression. The underlying substrate is composed of unconsolidated marine sediments. In certain sectors, a spatial overlap with Posidonia oceanica meadows occurs.

The aforementioned characteristics hinder their cartographic representation using traditional methods, such as aerial image interpretation and hillshade maps derived from bathymetric data, particularly for thin structures located at greater depths and in areas where Posidonia oceanica meadows are present.

The aim of this study is to evaluate the usefulness of the Red Relief Image Map (RRIM) method as an alternative quantitative terrain visualization tool for the cartography of submerged beachrocks. This method is based on the quantitative attribute openness, which expresses the degree of dominance or enclosure of a location on an irregular surface and enhances concave (negative openness) and convex (positive openness) features. Using this attribute, the RRIM method combines three main elements: topographic slope, positive openness and negative openness, allowing the visualization of subtle, low-relief topographic structures on apparently flat surfaces.

Using this approach, this study aims to improve the identification and cartographic delineation of submerged beachrock levels and to define optimal visualization parameters that contribute to a better understanding of the beachrock sequence.