Author(s): Marcos Sanz-Ramos; Ernest Blade; Josep Dolz

Linked Author(s): Marcos Sanz Ramos

Keywords: Nalcollar; Mine disaster; Spilled volume; Hydraulics; Hydrology

Abstract: On the early hour of April 25th 1998, the tailings pond of the mine complex of Aznalcóllar (Spain) failed. The stored fluid was released travelling tens of kilometres along the Agrio and Guadiamar rivers, almost reaching the Doñana National Park. The fluid was retained within riverbeds and floodplains (mud-like fluid) and in the Entremuros area (water-like fluid). Current research reveals more than 400 scientific publications since the accident, but the main research are not focussed on “Hydrology” and “Hydraulics” topics. However, nowadays some discrepancies regarding these topics can be found, especially on the spilled volume from the pond. Aiming to show some light in this regard, this document presents a recompilation of the spilled volume found in the literature, which generally ranges from 0.45 to 10.32 hm³. Data inferred from some authors (rating curves plus registered hydrograph) increase this volume up to 14.4 hm³. However, this volume might overtop the pond capacity just before the accident, and it would be near to the limit of the maximum pond capacity extracted from a post-failure topographical data (15.4 hm³). New hydrometeorological data is presented and analysed, in particular the five nearest rainfall station to the basin and two water-level gauge station, one of them located 7.1 km downstream of the pond. An analysis of these data shown that the spilled volume would have been around 11.5 hm³, more than twice of the value generally reported in the literature (5 hm³) but far from the potential storage capacity of the pond. On the other hand, natural runoff during the weeks after the accident generated an extra volume that probably increased the retained volume, mainly in the Entremuros area. A simple rainfall analysis, contrasted with the two gauge stations, shown that around of 5 hm³ entered into the affected area and potentially reached Entremuros, which had enough capacity to store this extra volume. Finally, the volume recovered during the restoration activities also presents discrepancies. Values found in the literature ranges from 4.7 to 10 hm³, but around 7 hm³ are generally presented in the literature. Differences between the spilled and the recovered volume can be due to the natural hydrological processes, mainly infiltration and/or the evaporation of the water-like part of the spill.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022446

Year: 2022