Apr 20th, 2018
The horizontal axis shows the dams of a real life sample dam portfolio.
The four left green bars correspond to benchmarking values, namely:
Mount Polley and Samarco annual probability of failure evaluated with the
ORE2-Tailings methodology, the min-max values of the worl-wide portfolio
based on historic records and the values obtained by a Ph.D. Thesis at
UBC which attempted a theoretical estimate of the annual probability of
failure of standard and dewatered tailings. The vertical axis bears the
annual probability of failure. For each structure a yellow bar depicts the
Uncertainty related to the probability estimate.
The portfolio bench-marking shows that in the considered case there are
dams below the historic benchmark. Some overlap the benchmarks limits
and some are above the upper limit, however still significantly lower than
the Mount Polley or Samarco estimates. Additional studies and information
allow to narrow the uncertainties (length of the yellow bars). Mitigation will
push the bar down. Long term lack of maintenance, climate change effects
will tend to push the bars up. The combination of this graph with the cost
functions for each dam gives the risks (see next figure). Interdependent
dams can be analyzed and their effect included in the portfolio analysis.