Canadian Dam Association Bulletin - Fall 2017 - 19

1. INTRODUCTION
Risk assessment for dams, and
in particular tailings dams, have
attracted significant recent interest
(Caldwell, 2016, Wise, 2014) due to the
occurrence of large failures. Widely
reported by worldwide media were
Mount Polley, B.C., Canada, in 2014,
and Samarco, Minas Gerais, Brazil,
also in 2014 (Caldwell et al., 2015).
Significant failures come together
with a swarm of minor problems which
could be considered near misses. Just
to quote a local Canadian example,
there were 46 dangerous or unusual
occurrences at tailings ponds at mines
across B.C. between 2000 and 2012,
according to the annual reports of
the chief inspector of mines of British
Columbia (Hoekstra, 2014).
Inexperienced personnel and the
public often consider a few years of
stable behaviour as an assurance of
long-term safety, despite stark warning from experts. For example: "For
any engineer to judge a dam stable for
the long-term simply because it has
been apparently stable for a long period of time is, without any other substantiation, a potentially catastrophic
error in judgment" (Szymanski and
Davies, 2004).
Geotechnical risk assessment literature is wide-ranging and can be
considered mature. However, careful
review shows significant gaps, making
it difficult for a professional willing
to tackle a risk assessment to grasp
the road map necessary to go from
gathering basic data to true definition of risks. Back in 1984, Whitman
wrote, "Unfortunately, probability still
remains a mystery to many engineers,
partly because of a language barrier
and partly from lack of examples
showing how the methodology can
be used in decision-making process."
Examples of pertinent literature
range widely, covering:
* theoretical approaches that show
general geotechnical examples (Ang
and Tang, 1975, 1984, Harr, 1984,
Fenton, 1997);
* detailed approaches (Baecher, 1987);
* historical phenomenological
approaches which tackle specific
aspects of past nefarious events
Canadian Dam Association * Fall 2017

(Jeyapalan, 1980, Lucia, 1981, Azam
and Li, 2010, Oboni and Oboni, 2013);
* probabilistic approaches (Fell et al.,
2000, Hamade et al., 2011, Silva
et al., 2008, Oboni and Oboni, 2014,
2016b, Oboni et al., 2014);
* to guidelines (CDA, 2007, 2014,
ANCOLD, 2011) which often talk
about risk without actually going in
any practical evaluation, especially at
mine closure (Szymanski and Davies,
2004).
Readers will note that the terminology in the literature is often poorly
defined, with risk used as a synonym
for probability. With other ill-defined
concepts, this leads to ubiquitous confusion among professionals, adding
to the language barrier that Whitman
was already mentioning back in 1984.

2. TAILINGS DAMS AND
ENTERPRISE RISKS: THE NEED TO
AVOID INFORMATIONAL SILOS
Mine operations often constitute a
complex management conundrum as
various internal and external stakeholders compete for risk mitigation
and other operational decisions. With
high risks to their owner, tailings
dams tend to be treated as informational silos due to the gut feeling they
generate. This is not necessarily a true
evaluation of their condition due to
complexity and difficulty in evaluating their true state of health.
LePoudre et al. (2016) have shown
the benefits brought by the application of enterprise risk management in
dealing with risks on tailings dams.
The need to avoid informational silos
and to combine all risks, including, of
course, those potentially generated by
tailings dams, has been demonstrated.
To eliminate those silos, it is necessary to use an approach to risk evaluation on dams which is lean, quantitative,
and easy to implement. It must allow
early prioritization of actions while
avoiding the common pitfalls of risk
assessments (Oboni et al., 2016).

3. CASE HISTORY
A mining operation is composed of
numerous elements such as tailings
dams and ponds, pumps, pipelines,
ditches, weirs, etc. Elements are all

exposed to numerous natural or manmade hazards leading, but not limited, to
potential problems of stability, erosion,
overtopping, internal erosion, concrete
failure, etc. (Oboni and Oboni, 2016a).
The system in the case history considered in this paper is illustrated in
Figure 1. It includes seven (7) ponds
and a portfolio of fifteen (15) relatively
small dams, less than 30m high, spread
over four (4) distinct operations. To
stay brief in this article, ancillary
elements such as pipes, weirs, water
treatment plants, etc., were not considered in the analysis.
Each dam has its own failure consequences due to:
* various physical parameters of the
storage such as total volume, water
content, and viscosity;
* potential breach characteristics,
dimensions, and outflows;
* land occupation downstream of the
dams, which consists of a combination of agricultural land, residences,
fresh water bodies, and transportation corridors.
Thus, the definition of the probabilities of failure and the specific
risk assessment for each dam is a very
onerous task if performed in detail
at each location. Meanwhile, it is of
paramount importance for the client
to quickly grasp where his major risks
lie. This permits mitigation of potential emergencies and allows to focus
efforts in the right direction. This was
the mission that was given by the portfolio owner.
Detailed in the next sections, external and internal hazards were identified for each of the seven (7) ponds.
Hazard or failure scenarios were constructed, either with single elements
or with compounded ones. Potential
consequences were identified, and the
process was completed by evaluating
the risks.
Hazard scenarios are defined as
any malfunction, or deviation from
the intended level of performance, of
the system or of any of its elements.
Blatant negligence such as the adoption
of insufficient factors of safety, inadequate site investigations, lack of quality
control are not hazards; they fall in the
realm of negligence (Riskope, 2011).
19



Table of Contents for the Digital Edition of Canadian Dam Association Bulletin - Fall 2017

Board of Directors
President’s Message
2018 Board of Directors Update
2017 CDA Awards
Screening Level Risk Assessment for a Portfolio of Tailings Dams
Dam Safety Review, Public Safety Workshops Hit the Road
CDA Events Photospread
Gardiner Dam 50th Anniversary
Jim’s Journey – Memoirs by Jim Gordon
CDA Launches Digital Editions of Guidelines
Invitation From Icold 2018 in Vienna
Icold Corner
Notice of the Annual General Meeting
Ouranos Press Release – 2017 Spring Floods in Quebec
CDA Young Professionals
CDA 2018 Conference
Time to Renew Your Membership
CDA News Brief
Buyers’ Guide and Trade List
Canadian Dam Association Bulletin - Fall 2017 - Intro
Canadian Dam Association Bulletin - Fall 2017 - cover1
Canadian Dam Association Bulletin - Fall 2017 - cover2
Canadian Dam Association Bulletin - Fall 2017 - 3
Canadian Dam Association Bulletin - Fall 2017 - 4
Canadian Dam Association Bulletin - Fall 2017 - 5
Canadian Dam Association Bulletin - Fall 2017 - 6
Canadian Dam Association Bulletin - Fall 2017 - Board of Directors
Canadian Dam Association Bulletin - Fall 2017 - 8
Canadian Dam Association Bulletin - Fall 2017 - President’s Message
Canadian Dam Association Bulletin - Fall 2017 - 10
Canadian Dam Association Bulletin - Fall 2017 - 11
Canadian Dam Association Bulletin - Fall 2017 - 12
Canadian Dam Association Bulletin - Fall 2017 - 13
Canadian Dam Association Bulletin - Fall 2017 - 2018 Board of Directors Update
Canadian Dam Association Bulletin - Fall 2017 - 2017 CDA Awards
Canadian Dam Association Bulletin - Fall 2017 - Screening Level Risk Assessment for a Portfolio of Tailings Dams
Canadian Dam Association Bulletin - Fall 2017 - 17
Canadian Dam Association Bulletin - Fall 2017 - 18
Canadian Dam Association Bulletin - Fall 2017 - 19
Canadian Dam Association Bulletin - Fall 2017 - 20
Canadian Dam Association Bulletin - Fall 2017 - 21
Canadian Dam Association Bulletin - Fall 2017 - 22
Canadian Dam Association Bulletin - Fall 2017 - 23
Canadian Dam Association Bulletin - Fall 2017 - 24
Canadian Dam Association Bulletin - Fall 2017 - 25
Canadian Dam Association Bulletin - Fall 2017 - 26
Canadian Dam Association Bulletin - Fall 2017 - 27
Canadian Dam Association Bulletin - Fall 2017 - 28
Canadian Dam Association Bulletin - Fall 2017 - 29
Canadian Dam Association Bulletin - Fall 2017 - Dam Safety Review, Public Safety Workshops Hit the Road
Canadian Dam Association Bulletin - Fall 2017 - 31
Canadian Dam Association Bulletin - Fall 2017 - 32
Canadian Dam Association Bulletin - Fall 2017 - 33
Canadian Dam Association Bulletin - Fall 2017 - CDA Events Photospread
Canadian Dam Association Bulletin - Fall 2017 - Gardiner Dam 50th Anniversary
Canadian Dam Association Bulletin - Fall 2017 - 36
Canadian Dam Association Bulletin - Fall 2017 - 37
Canadian Dam Association Bulletin - Fall 2017 - Jim’s Journey – Memoirs by Jim Gordon
Canadian Dam Association Bulletin - Fall 2017 - CDA Launches Digital Editions of Guidelines
Canadian Dam Association Bulletin - Fall 2017 - Invitation From Icold 2018 in Vienna
Canadian Dam Association Bulletin - Fall 2017 - Icold Corner
Canadian Dam Association Bulletin - Fall 2017 - 42
Canadian Dam Association Bulletin - Fall 2017 - Notice of the Annual General Meeting
Canadian Dam Association Bulletin - Fall 2017 - Ouranos Press Release – 2017 Spring Floods in Quebec
Canadian Dam Association Bulletin - Fall 2017 - 45
Canadian Dam Association Bulletin - Fall 2017 - CDA Young Professionals
Canadian Dam Association Bulletin - Fall 2017 - 47
Canadian Dam Association Bulletin - Fall 2017 - CDA 2018 Conference
Canadian Dam Association Bulletin - Fall 2017 - 49
Canadian Dam Association Bulletin - Fall 2017 - Time to Renew Your Membership
Canadian Dam Association Bulletin - Fall 2017 - CDA News Brief
Canadian Dam Association Bulletin - Fall 2017 - 52
Canadian Dam Association Bulletin - Fall 2017 - 53
Canadian Dam Association Bulletin - Fall 2017 - Buyers’ Guide and Trade List
Canadian Dam Association Bulletin - Fall 2017 - cover3
Canadian Dam Association Bulletin - Fall 2017 - cover4
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