Revisiting the Hydraulics of the Aznalcóllar Mine Disaster

Abstract

The Aznalcóllar tailings pond failure (1998) is regarded as one of the severe ecological mine disasters ever reported. The spill of the mine tailings affected more than 60 km of the Agrio and Guadiamar rivers and caused major environmental damage. Despite the event being well-documented with more than 400 scientific publications, including two special issues and two reviews, several hydraulic uncertainties and inconsistencies remain. This paper conducts a state-of-the-art review of the most relevant hydraulic aspects of the mine disaster. It addresses the pond and fluid characteristics, the break type, the breaking time, the flow propagation, the volume potentially stored and subsequently spilled, area dimensions affected by the spill, and the morphological changes generated in the river and riverbanks caused by the spill, and later on by the restoration activities. Several discrepancies and plenty of controversial data have been unearthed that may affect general understanding of the event. In addition, new data is introduced and analysed applying photointerpretation and digital terrain analysis techniques, aiming to derive in essential hydraulic parameters. The most important findings are that the spill could have had a volume about 11.5 hm3, affecting about 86.7 km of river length, twice the most referenced values in the literature, and that applied restoration activities have substantially modified the hydro-sedimentary processes of the affected system. Additionally, a first video observation-based classification reveals that the fluid behaved more like a highly concentrated sediment-laden flow than like a mud flow.

Discrepancies on the spilled volume in the Aznalcóllar mine disaster

“…Until 29 September, according to the CHG data, the area affected by the spill accumulated at least 5.4 hm 3 of additional acid waters (no-data of other inputs in the subbasin are available). This value agrees well with the 5 hm 3 of acid waters retained at Entremuros (Arenas et al, 2001;CHG, 2005;) and with the retained potential capacity of fluid of the Entremuros area (AGE and JA, 1999;OAPN, 1998;Sanz-ramos et al, 2022). Thus, approximately less than a half of the runoff was not treated.…”

“…In the literature there seems to be a general agreement in the amount of the spilled volume, considered to be about 5-6 hm 3 . Despite that, there still persist significant uncertainties regarding the spilled volume, among others hydraulic parameters (Sanz-ramos et al, 2022). A prove of that is not only the wide range of values found, but also the scarcity of studies that have attempted to reproduce the flood by using numerical methods.…”

A Probabilistic Approach for Off-Stream Reservoir Failure Flood Hazard Assessment

“…Despite it not only being applied to irrigation ponds (water, "Newtonian" fluid-like), there is no limitations to use it, for example, in mine tailing ponds (muds, non-Newtonian fluid-like). This approach can help in the development of ad hoc guidelines that allow the complexity of fluid, tailings, and dam failures to be considered in order to properly characterize potential breach and runout scenarios [20,43].…”

“…Off-stream reservoirs are defined as human-made structures designed for the storage of any kind of fluid-usually water and mine tailings-located outside the basin's channel network and totally or partially delimited by a retention dyke. They are essential structures for different purposes, such as: water supply to small populations, irrigation, cattle raising, firefighting, purification, recreation, mine tailings, and electric facilities, among other uses [19][20][21][22][23].…”