January 2004 ISSUE
EXPERT'S CORNER
Climate Change — An Adaptation
Challenge for Northern Engineers
BY DON W. HAYLEY, P.ENG.
(click on images to view)
Canada’s scientific community continues to preach the climate change message, constantly reinforcing the belief that observed climatic warming trends are greatest in the north. Design engineers who provide services on northern projects may find the array of published predictions from global circulation models confusing, but anyone who assesses the historical records from communities in the north, particularly the Mackenzie Valley, will find the evidence for a climatic warming trend rather compelling.
The air temperature in the valley has, in fact, warmed about 1.7 C° over the past century, according to Environment Canada.
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The Canadian Council of Professional Engineers held a workshop last February to examine the role of Canada’s engineers in adapting to climate change. This article is a brief summary of a presentation I made at the workshop. It describes our success at EBA Engineering Consultants Ltd. implementing a procedure into our practice that explicitly recognizes climate change as one more variable to be considered for design of structures on permafrost foundations.
The Intergovernmental Panel on Climate Change concluded in the early 1990s
that arctic regions are particularly vulnerable to climate change, partially
because of a perceived concern about widespread thinning or disappearance of
permafrost.
Environment Canada formed a project group with funding from the Panel on Energy
Research and Development to establish guidelines for permafrost engineering design.
The objective was to provide a strategy for incorporating climate change into
long-term planning in Canada’s North.
The results were presented in an Environment Canada report, Climate Change Impacts
on Permafrost Engineering Design (1998). The study team comprised government
scientists, academics and practitioners prominent in northern climate and permafrost.
Early skepticism about the outcome turned into acceptance and support for a project
screening tool that has been in common use at EBA for the past five years. Implementation
and application of the risk-based principles from that process to many projects
have proven to be both rational, and to pass the test of peer and regulatory
reviews.
Project Screening
For Climate Change Risks
A project is screened to determine its sensitivity to climate change, identified
as a probability that climate change will adversely affect permafrost soils or
rock that must remain frozen to ensure stability of any structure it supports.
Secondly, the consequences of any change, should it actually occur, are examined.
The screening process schematic is shown here. The relationship between sensitivity
and consequence define the risk that climate change imposes on the project. A
criterium is provided in the study report that establishes the level of analysis
that is appropriate for project design, based on the risk of failure.
The analysis complexity can range from no action required or simple qualitative
assessment based on judgment to complete quantitative analyses supported by complex
ground thermal modeling tools.
These quantitative analyses require cautious attention and documentation of the
input parameters that describe the climatic effects over the life of the structure
and their annual variability. Specific guidance is provided in the study report
on how to assess the sensitivity and the consequence level for any project.
Three projects from EBA files were used in the February workshop to demonstrate
how the system has been adopted into our engineering practice. They included
a water dam with a permafrost core at Ekati Diamond Mine, a complex building
foundation in Inuvik, and upgrading of the primary highway leading to Yellowknife.
That highway lies over particularly sensitive, discontinuous permafrost.
The relative positions of these projects on the risk chart are shown in the attached
figure.
For this discussion, I will describe only the building in Inuvik as it embodies
all of the facets of the project screening system.
Inuvik Regional Health Centre
The new regional health centre, constructed in Inuvik in 2001/02, required
an innovative approach to foundation design for permafrost soils prone to substantial
settlement if allowed to thaw.
Most previous foundations for large buildings in Inuvik have been elevated and
supported on timber or steel piles frozen into the underlying permafrost. Over
the years, this type of foundation system has fallen out of favour for architectural,
functional, esthetic and cost reasons.
An alternative and somewhat high-tech foundation solution is to intercept heat
transferred from the structure to the underlying permafrost with two-phase heat
pipes or thermosyphons. These passive cooling devices extract heat from below
the structure and dissipate it to the atmosphere during the cold winter months.
The mechanical components are designed, manufactured and installed by Arctic
Foundations of Canada Inc. The geotechnical design requires two-dimensional heat
flow analyses in order to configure the piping system required to confirm long-term
thermal stability of the underlying permafrost.
The principal variable in such analyses is the anticipated variability of outside
air temperatures and any climatic trends that could affect future long-term performance.
Application of the screening principles to this project identified that the
permafrost sensitivity was high because of the presence of abundant shallow ground
ice within the Town of Inuvik. The failure consequence was rated as major or
medium to high because the structural design has a low tolerance for differential
movements and the economic or social impact of hospital closure could be significant.
This placed the project into a high-risk category, requiring a complete quantitative
analysis of climate change effects. Comprehensive geothermal modeling of the
foundation system was required, adding considerably to the complexity and cost
of the foundation system design.
The foundation design included a probabilistic evaluation of Inuvik air temperature
records in order to anticipate long-term trends for a design service length of
30 years starting in 2000. The results were interesting because they show that
all five years preceding 2000 were well above the mean, and the 43 years of record
and one warm year (1998) had a 1/100 annual exceedance probability For this project
the design was tested for all of the following scenarios:
• Five consecutive 1/5 annual exceedance probablity warm years followed
by a 1/100 AEP year,
•
Ten consecutive 1/5 AEP years,
•
Warming trend of 0.47 C° per decade.
The design was judged appropriate for any one of the above climate variability scenarios.
Climate change can be considered one more variable to be considered within
a probabilistic framework for the design of northern structures. This is particularly
true where stability of underlying permafrost soil or rock is essential to long-term
performance.
Application of climate change principles to design still requires considerable
judgment because regional climatic trends are poorly defined and the literature
contains conflicting information that, if taken at face value, could stifle rational
northern development.
Reference: Etkin, D., 1998, Climate Change Impacts on Permafrost Engineering
Design. Internal report by Environmental Adaptation Research Group, Environment
Canada.
Don Hayley, P.Eng., is principal engineer at EBA Engineering Consultants Ltd.
He has been active in northern engineering worldwide for more than 30 years.
Editor’s Note: This article is the second in a series presented by APEGGA's Environment Committee regarding the role of professional members in sustainability, climate change impact and adaptation. These articles will address industry specific initiatives, international initiatives, and regulatory considerations - meant to raise the level of awareness and generate discussion. The opinions expressed by the author are his own and not necessarily those of APEGGA.