Assessing the long-term integrity of the tailings dam in the dynamic tropical landscape of the Philippines

Tailings dams, designed to store mining by-products, can significantly alter the landscape and, if not properly maintained, can pose long-term environmental risks. There is a wealth of research on the rapid/sudden failure of tailings dams, but comparatively little on how they may gradually fail over time, due to natural erosional processes. This issue is paramount if tailings storage is left unmanaged, especially within an environment with high background rates of erosion and sediment transport. This study investigates the Antamok Valley Fill Tailings Dam in Benguet (the Philippines), unused for tailings storage from large-scale mining since 1998, which has become susceptible to continued infilling, overtopping, and potential erosion of its dam wall. Using state-of-the-art numerical modelling, this research assesses the long-term integrity and geomorphological impacts of the dam, including changes in dam storage capacity due to infilling and the downstream impact of potential release of tailings through overtopping and erosion of the dam wall. We used an IfSAR digital elevation model (DEM), observed hourly rainfall, and field-derived grain size distribution as inputs to a CAESAR-Lisflood to numerically simulate centennial changes in the dam and their impact on local topography. Our preliminary results indicate that dam infilling leads to a progressive reduction in water storage, causing increased episodes of overtopping that accelerate erosion along the dam wall and the deposition of tailings in the surrounding area downstream. This study highlights the importance of regular monitoring and maintenance of legacy tailings dams to mitigate their potential environmental impacts. Given the risks of continued infilling, overtopping, and erosion, long-term management strategies are necessary to prevent further structural degradation and associated hazards.

Keywords: Tailings Dam; Sediment transport; Geomorphology; Philippines