Evaluating the applicability of a terrain-based floodplain delineation tool for a broad-scale assessment of flood exposure of tailings deposits

Abstract. Construction and abandonment of mine tailings deposits in river floodplains have created environmental risks associated with the release of toxic substances during floods. Assessment tools are needed to understand levels of risk and to prioritize sites for management. These tools need to be computationally efficient over wide areas, potentially whole river basins, which generally excludes reliance on 2D hydrodynamic models. This research evaluates the applicability of a terrain-based floodplain delineation tool (GFPLAIN) to assess flood exposure of tailings deposits by comparing its results against a 2D hydrodynamic model, the Shallow Water Integrated Flood Tool (SWIFT). For this compassion, the case study area of Copiapó River Basin (Atacama, Chile) was used to model two flood scenarios, the extreme flood event of March 2015, and a hypothetical flood with a 100-year return period. Overall, the GFPLAIN flood maps showed limitations in reproducing the list of tailings deposits identified as exposed by SWIFT, with some agreement between some of the top 10 deposits prioritized by these tools. We conclude that GFPLAIN, while fast to apply and potentially able to prioritize sites at risk, has limitations in providing an accurate and complete assessment due to its limited consideration of local terrain and flood dynamics.