Key Steps for Conducting Tailings Dam Breach Studies

Key Steps for Conducting Tailings Dam Breach Studies

Author: AJ Strauss, V Martin, D Fontaine, J Cathcart
Conference: 84th Annual Meeting of International Commission on Large Dams
Date: May 15-20, 2016

ABSTRACT
Engineering practitioners currently use a combination of guidance documents, published papers, and professional experience to support tailings dam breach and inundation studies. There is considerable knowledge and information available in this relatively new field of practice, but standardised and comprehensive guidelines specific to tailings dams are not available. Practitioners face several key challenges: (a) the more established and mature guidance is typically focused on water storage dams; (b) the available literature may only address specific aspects of dam breach assessment and inundation modelling; (c) the available literature sometimes relies on historical data that may not be consistent with the proposed application; and (d) the results are highly sensitive to the selected modelling inputs. This paper reflects on the currently available literature on tailings dam breach and inundation studies, compares how the major components for these studies are approached, and discusses how the resulting conclusions may vary. The key aspects of tailings dam breach and inundation assessment that are considered include: initial conditions and  hydrology; boundary conditions; breach parameters; tailings mobility and discharged volume; and flood routing and inundation mapping.

INTRODUCTION
Martin, Fontaine and Cathcart (2015) prepared the paper, “Practical Tools for Conducting Tailings Dam Breach Studies” for the Canadian Dam Association Conference. This paper builds onto that and
will provide the South African context.

Tailings dam breach studies are becoming generally expected and often required for operating and planned Tailings Storage Facilities (TSFs). The guidelines that are typically followed by practitioners around the world for tailings dam breach analyses were originally developed for water retaining dams, and as such, are not fully applicable to tailings dams. Generally, international guidelines don’t prescribe procedures for conducting tailings dam breach analyses.

Tailings dam breach studies are being requested for various purposes listed below. The suitability of these studies for such purposes is not reflected on, or discussed in this paper.

  • To determine the dam hazard classification based on potential incremental consequences of failure to socio-economic and environmental values;
  • To prepare inundation maps in support of emergency preparedness and response planning;
  • As part of the environmental studies for a proposed new project or expansion of an existing project;
  • As part of alternatives assessments to evaluate various TSF locations or alternative tailings storage technologies.

Dam breach studies include characterisation of a hypothetical dam breach, flood wave routing, inundation mapping, and evaluation of impacts to socio-economic and environmental values. Standardised procedures and guidelines for conducting tailings dam breach studies do not exist at this time in South Africa. Mining and dam safety practitioners across the world are making efforts to standardise the procedure and are struggling with the practicalities of conducting meaningful assessments when every step of the process is inherently uncertain.

A range of methods may be applied in each step of the analysis depending on the extent of information available and the level of accuracy needed. A wide range of options is left open to practitioners in terms of how to conduct the assessment. The most appropriate approach and the accuracy of the results that can be achieved will be driven by the availability, resolution and accuracy of the input data. Increased complexity does not always result in increased accuracy, and as such, complexity should not be an objective, but rather a tool to be used carefully. Considering all this, a preliminary high level assessment may very well provide a sufficient level of detail to meet the stated purposes of a dam breach study.

A frequently cited reference specific to tailings dam breaches is by Rico et al. (2007) that presents empirical relationships for outflow volume, runout distance and peak discharge based on past tailings dam failures. Even though there are over 200 known cases of tailings dam failures worldwide, the documentation of these cases is often incomplete. Relationships developed by Rico et al. (2007) are based on 28 historic tailings dam failures for which complete data on runout distances and outflow volumes were available.

This paper is intended as a starting point for ongoing discussion about what approaches and methods are best suited to specific aspects of tailings dam breach and inundation studies. Key steps in conducting these analyses are identified and some practical tools are proposed with the objective of providing practitioners with information that will allow them to use the available literature and avoid potential difficulties that have been identified through our experience.

 

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