Morphodynamic evolution of depth-dependent sand mining pits and implications for sustainable sand mining

The demand for marine aggregates, particularly sand, is rapidly increasing due to population growth and the need for climate change adaptation. While sand extraction supports many essential industries, it also generates substantial environmental impacts, including habitat degradation and coastal erosion, underscoring the need for effective regulatory frameworks. Previous studies suggest that nearshore sand mining can contribute to coastal erosion; however, the impacts of sand mining pits at different water depths remain poorly quantified and are often addressed only qualitatively.

This study investigates the influence of water depth on sand pit morphodynamics and the long-term evolution of mining pits. Bathymetric datasets acquired between 2017 and 2024 from the Korea Hydrographic and Oceanographic Agency (KHOA) were analyzed for multiple sand mining pits located within the 25–65 m isobaths. Results show that pit recovery rates varied following three years of intensive mining. Linear regression between water depth and mean depth change revealed a weak but consistent negative relationship (R² = 0.40), indicating reduced sediment deposition with increasing depth, likely due to decreasing bed shear stress and sediment mobility.

These findings suggest that sand mining at greater depths may reduce morphological impacts on surrounding seabed areas, highlighting water depth as a critical factor in site selection and pit design. Because wave-induced bed shear stress is stronger in shallower waters, this study provides quantitative evidence to support depth-based guidelines for sustainable sand mining and informs future policy development.