attach_4_flood risk assessments in canada

8/8/2019 Attach_4_Flood Risk Assessments in Canada

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i n nova t i on Nov emb e r /D e c em b e r 2009 23

Floods: A Global CurseFloods are the most widespread and most signicant

geohazard on Earth in terms o economic cost and loss o

lie. Red Cross data or the period 1971-1995 indicate thatriver and coastal oods, in an average year, kill more than

12,700 humans, aect 60 million people, and render 3.2

million homeless. Te number o extreme ood disasters

requiring international assistance has grown: in the years

1990-1998 it was higher than in the previous 35 years(1950-1985) combined. In Canada, ood events have

claimed the lives o at least 200 people during the 20th

century, with over $2 billion in damage, a statistic that

emphasizes that oods in industrialized nations typically

result in low human losses (a notable exception is the1,200 atalities due to Hurricane Katrina) but very high

economic losses (similar to landslides). Additional major

ood events may be expected in the coming decadespartially due to predicted increase in the requency o

extreme weather events, but most importantly because

o densication o urban development and inrastr uctureon ood-prone terrain.

Hazard versus RiskIn Canada as in many other developed nations, ood

hazard management is predicated largely on an arbitrary

return period ood. Tis design ood orms the basisor the design o bridges, dikes and other ood protection

measures. Economic or lie loss potential is not explicitly

considered, irrespective o increased development in ood-

prone areas. Tus, even in the absence o any long-term

increase in ood hazard, ood risk must increase. Tisparadigm is exemplied in Figure 1.


features

An Appeal for

Flood Risk Assessmentsin Canada

Dr Matthias Jakob PGeo, Dr Mike Church PGeo, Kris Holm PGeo,

Dwayne Meredith, Neil Peters PEng, Hamish Weatherly PGeo


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Figure 1 would need to be adjusted i, or example,

ood hazard is expected to increase as a consequence o

net sediment deposition that decreases the conveyance

capacity o the channel, long-term changes o ood-producing hydroclimatic events, sea-level changes, long-

term and widespread environmental changes caused by

land use, reduction o glacial cover and beetle inestations

that may alter the long-term lood hazard. Flood

mitigation upgrades (dike improvements, oodways,river diversions) may partially neutralize any increased

ood hazard. But protective measures almost never

keep up with the increase o development. For the vast

majority o developed Canadian oodplains, total oodrisk has increased in proportion to development density,

local business activity, and additional economic activity

associated with ra ilways, pipelines, transmission lines,

telecommunication lines and highways.

Major recent river ood events in Europe as well as the2005 New Orleans sea-borne ood disaster have orceully

reminded society and decision makers that engineered

protective works cannot guarantee paramount saety, and

that the residual risks are higher than previously thought.

Tese and earlier ood disasters have increased worldwide

interest in lood warning systems and quantitative

ood risk assessments and have led to a paradigm shiin Europe rom a rule-based approach (ood hazard

assessments) to a risk-based process. On November 26,

2007, the European Directive on the assessment andmanagement o ood risks was enacted. It outlines a set

o actions on preliminary ood risk assessment, ood riskmapping and the preparation o ood management plans

to be completed by the end o 2015. Te directive covers

coastal oods, urban and groundwater oods, mandates

basin-scale planning and requires consideration o the

potential impacts o climate change on ood conditions.Te use o the phrase Management o Flood Risk in

the directives title emphasizes that European ood

philosophy has evolved rom attempts at ood control to

the management o ood risks.

Quantitative Flood Risk AssessmentsA hazard is an ex isting or potential uture event with anadverse eect. In contrast, risk is deined as the product

o the likelihood o a hazard occur ring and its anticipated

consequence. Vulnerable assets may include residential

developments and inrast ructure, business developmentsand activities on the loodplain, business activities

associated with transport o goods and services, as well

as social, ecological and historical values. Estimation

o consequence includes a comprehensive inventory o

values, ollowed by analysis o potential damage or lossor various event scenarios.

Procedures or natural hazard identication and risk

assessment guide decision makers and

the public to minimize risks rom these

hazards; however, it is rarely possible

to completely eliminate them, and

residual risks are a act o lie. Where

the consequences o a particular natural

hazard are largely economic in nature,

the risk management process is suited to

risk cost benet analysis and economic

optimization techniques. A limitation

is that these techniques ail to address

ecological, archaeological and social issues

because they are diicult to quantiy.

Tese are increasingly included in holistic

semi-quantitative approaches.

Quantitative Flood Risk Assessments

(QFRA) evaluate the likelihood and

consequences o looding, and relect

possible combined contributions to ood

risk o various operational, hydrologic,

hydraulic, and geotechnical actors. By

taking into account both ood likelihood,

(including the likelihood o dike breaches)

and consequence, risk-based approaches

oer a systematic way to identiy locations

o high risk that occur not necessarily

24 Nov emb e r /D e c em b e r 2009 i n nova t i on

f ea tu re s

Total Flood Risk

Floodplain

DevelopmentFlood hazard

C

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rom changes in ood hazard, but rather due to increases

in the vulnerabilities and consequences o a ood. Tey

also allow a transparent and repeatable evaluation o

potential ood mitigation alternatives, permit comparison

o ood risk to other risks aced by society, and help dene

thresholds or the tolerance o ood risk. Tis method

is thus well suited to allocate public resources directedtoward ood risk reduction.

In contrast to QFRA, ood management in British

Columbia has traditionally been based on ood hazard

(likelihood), as measured by the expected height o a

design lood augmented by a standard increment o

dike height (reeboard). Consequence is included only

implicitly in that it orms the motivation or a particular

assessment (eg, assessments would occur only in locations

with potential consequence). For example, or the Fraser

River, the design ood is the largest ood on record (1894),

the return period o which has not been dened with great

certainty, though ood requency analysis estimates a

probability o approximately 500 years. Recent consultingreports have shown that existing dikes ail to contain

design ood levels or even a 200-year return period ood

(roughly equivalent to the 1948 ood). Tis act and the

extremely high consequences o an extreme ood suggest

that a purely hazard-based approach may no longer provide

a rational decision tool or eective ood management.

Where to go from here?BGC Engineering in collaboration with the City o

Chilliwack, erasen Gas, Kinder Morgan Pipelines,

Indian and Northern Aairs Canada, the Ministry o

ransportation and Ministry o Environment recently

completed a pilot lood risk assessment

or the City o Chilliwack that addressed

economic risks to the area and pointed

toward vulnerabilities o populations living

on the Fraser River and other oodplains.

Te study demonstrated that a ood due to

dike breaches or overtopping could result

in overall direct damages approaching

$1 billion or the City o Chilliwack

alone. Furthermore, associated losses to

the BC economy have been estimated to

approximately $20 million per day. Tese

numbers demonstrate the extreme ood loss

potential along the lower Fraser River and,

by extrapolation, highlight that an extreme

Fraser River ood would likely turn into

Canadas most expensive natural disaster,

vastly exceeding the losses caused by the

Quebec Ice Storm o January 1998.

Similar, though in no way standardized,

studies are now underway or a handul

o other jurisdictions in BC ollowing the

Chill iwack example. Tese studies, however,

are not mandated by the provincial or

ederal governments but arise rom due

consideration by local government of cials

who recognise the compelling inormation revealed by

QFRAs. While this development is laudable, isolated

ood risk assessments that are not based on established

provincial guidelines ail to provide a province- or nation-

wide rational decision-making ramework. For example,

the BC ood protection und that was inaugurated in 2007

explicitly excludes scientic studies, but aims to provideunds or engineered ood protection. Clearly rom a

public perspective, a systematic quantication o ood

risk ought to orm the basis or where these limited unds

should be expended.

Where the anticipated consequences include the

potential or loss o lie, the decision-making process

requires that risks be compared against risk tolerance

criteria as a way to prioritize ood hazard risk management

activities. Quantitative tolerable risk or risk acceptance

criteria or natural hazards, including oods, have never

been dened by any British Columbia public governmental

agency. Notwithstanding, quantitative thresholds or

tolerable risk have been cited as a useul approach orthe evaluation o British Columbia oshore oil and gas

development and or residential developments.

A risk-based decision-making ramework or assessment

o ood hazards in Canada would be compatible with

Canadian and international guidelines or quantitative risk

assessment in that it would involve a systematic, transparent,

and reproducible method or assessing risk based on

both the likelihood o occurrence and the consequences

o an event. Floodplains o major Canadian rivers are

increasingly being used as principal inrastructure arteriesand undergo replacement o agricultural land by urban

development. Even though there are regulatory barriers


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26 Nov emb e r /D e c em b e r 2009 i n nova t i on

to converting armland into urban land, these barriers

tend to be thwarted in the long run whenever economic

incentives to overcome them become sufciently powerul.Furthermore, agriculture itsel is increasingly highly

capitalised. Tese inescapable political and social realities

emphasize the need or systematic and standardized ood

risk assessments or rational decision making in areasexposed to ooding. Tis need is urther emphasized notonly by the non-linearity o the development process, but

by uvial and hydroclimatic regime shis that may result

in changing ood requencies.

A uture extreme ood on a major Canadian river is

a statistical certainty as will be the consequent economiccosts and perhaps loss o lie. In the post-ood period,

government decision makers will be questioned by the

public as to the reasons or the extreme losses and why those

aected were not sufciently protected. A standardizedand systematically applied ood risk approach based in

legislation cannot avoid losses; however, it can provide the

much-needed rational basis or the optimal a llocation o

unds to those areas that are likely to suer the greatest

losses. his optimization o public resources oughtultimately to be the responsibility o elected government

ofcials. Political realities sometimes discourage science-

based decision making, which is partially because o the

ailure o the proessional community to communicate

their ndings eectively to the wider public. Rather thansuccumbing to this perceived dichotomy, it should motivate

engineering and geoscience proessionals, the general public

and local decision makers to urge their elected ofcials or a

shi towards a risk-based ood-management system.

Under the auspices o APEGBC, senior consultants,provincial government engineers and academics have

proposed the developement o a provincial ood hazard

proessional practice guideline that will explicitly address

risk and climate change actors. Whi le not replacing currentdirectives and regulations, the new guideline would serve

to promote a transition rom hazard to risk-based ood

management, at least in British Columbia. Ultimately, we

hope, this evolution will provide an improved decision-

making ramework in the ace o continuing social andeconomic development and ongoing climate change. v

Dr Matthias Jakob PGeo, Kris Holm PGeo and HamishWeatherly PGeo are with BGC Engineering. Dr Mike

Church PGeo is professor emeritus with the Department of

Geography at the University of British Columbia. Dwayne

Meredith is Manager, Strategic Mitigation Programs with

Emergency Management BC. Neil Peters PEng is Inspectorof Dikes with the BC Ministry of Environment.

f ea tu re s

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attach_4_flood risk assessments in canada

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