Historical Evaluation of Gravel Mining in Castellbisbal (Catalonia-Spain)

This study provides a historical assessment of gravel extraction in Castellbisbal, Catalonia, focusing on the Serrat de la Verdolaga area, where fluvial gravels were mainly mined for road construction, including the A-2 motorway. Although extraction began in the 1970s and continued intermittently until the mid-1990s, no official records of volumes were kept.

To address this, the research combines geophysical and cartographic techniques to estimate the original gravel volume and the amounts extracted over time. Electrical Resistivity Tomography (ERT), a non-invasive geophysical method, identified two main subsurface units: exploitable Zanclian gravels and underlying Burdigalian shales.

By integrating ERT data with digitized topographic maps from 1970, 1980, 1987, 1995, and 2023, digital terrain models were created to measure volumetric changes. Results show that the peak extraction occurred between 1970 and 1980, accounting for nearly 70% of the total removed material. About 1.1 million cubic meters of gravel remain, though their recovery is limited by existing electrical infrastructure. This multidisciplinary approach highlights the effectiveness of combining historical maps and modern geophysical methods to reconstruct undocumented resource exploitation activities.