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Modelling (mountain) flood risk
and managing its uncertainties
Francesco Ballio14 March 2016
DICA seminar
Francesco Ballio
2Abstract
Modelling (mountain) flood risk and managing its uncertainties
Hydraulic engineers fight against flood risk. However, most of the effort within
this battle has been devoted to the hazard component of the process, that is,
the forcing action (see DICA seminar by prof. Menduni, 2015). Parallel to this,
most of the scientific and technological progress has focussed on the forcing
phenomena. However, no "risk" can be assessed if the expected damages are
not evaluated; the latter are by far the least known part of the risk chain: data
are scarce and low-quality, damage models are, consequently, poor.
By means of a case study (Orvieto flood, 2013) this seminar is aimed at
discussing possible approaches to the assessment of the complete risk chain
and warning about the fragilities of available models.
Francesco Ballio
3Risk assessment: what for?
• land use planning (say, construction permission)
• design mitigation works (river training)
• emergency management (contingency plans)
• insurance costs
• …
… cost - benefit analysis
Francesco Ballio
4Structure of the seminar
Introduction
presentation of case study
the flood phenomenological chain
the structure of risk
flood risk
Flood risk assessment
hazard
exposure + vulnerability �
� damages
Case study
hazard
exposure + vulnerability �
� damages
discussion
flood risk assessment
Francesco Ballio
5Case study: presentation
Umbria 2012, town of Orvieto
Francesco BallioCourtesy of Claudio Margottini,
ISPRA
Case study: presentation
Rivers: Paglia and Chiani (confluence)
Francesco Ballio
7Introduction: the flood chain
hydrologicalprocesses
propagationalong river
flood
damages
atmosfericprocesses
Francesco Ballio
8Introduction: the flood chain
hydrologicalprocesses
propagationalong river
flood
damages
atmosfericprocesses
rain: i(t)
???
Francesco Ballio
9Introduction: the flood chain
propagationalong river
flood
damages
atmosfericprocesses
hydrologicalprocesses
rain: i(t)
discharge: Q(t)
Francesco Ballio
10Introduction: the flood chain
hydrologicalprocesses
flood
damages
atmosfericprocesses
propagationalong river
water depth: h(t)
discharge: Q(t)
Francesco Ballio
11Introduction: the flood chain
hydrologicalprocesses
damages
atmosfericprocesses
propagationalong river
flood
water depth: h(t)
flooded area: A(t)
Francesco Ballio
12Introduction: the flood chain
hydrologicalprocesses
atmosfericprocesses
propagationalong river
flood
damages
flooded area: A(t)
residentialbuildings
Francesco Ballio
13Introduction: the flood chain
hydrologicalprocesses
atmosfericprocesses
propagationalong river
flood
damages
flooded area: A(t)
commercial activities
agriculture
Francesco Ballio
14Introduction: the flood chain
hydrologicalprocesses
atmosfericprocesses
propagationalong river
flood
damages
flooded area: A(t)infrastructures
Francesco Ballio
15Introduction: the structure of risk
RISK = DAMAGE "+" PROBABILITY
Damage = f ( x1 , x2 , x3 , … , xN )
HazardExposure
Vulnerability
variables xi may be considered / treated either as stochastic or deterministic
How should we address this?
Probability
Francesco Ballio
16Introduction: the structure of risk
RISK = DAMAGE "+" PROBABILITY
Damage = f ( x1 , x2 , x3 , … , xN )
x1
xn
x3
x2
DamageD=0
For example:
x1 = rain quantity on a given day
x2 = river geometry
x3 = residential value in a given area
xi = …
xn = cars parked in a given area
Francesco Ballio
17Introduction: the structure of risk
RISK = DAMAGE "+" PROBABILITY
Damage = f ( x1 , x2 , x3 , … , xN )
x1
xn
x3
x2
DamageD=0
Another example (bridge collapse):
x1 = flow depth and velocity
x2 = bridge geometry
x3 = resistance of materials
xi = …
xn = traffic load
Francesco Ballio
18Introduction: the structure of risk
RISK = DAMAGE "+" PROBABILITY
DamageD=0
Damage = f(threshold)
Design: we basically consider only tails (to
be avoided � safety factors)
Risk Assessment: we need the shape of
the whole pdf
Safety factors are not of much help within
risk assessment
DamageD=0
Francesco Ballio
19Introduction: flood risk
hydrologicalprocesses
propagationalong river
flood
damages
atmosfericprocesses
causes
effects
Hazard
Damage = f ( x1 , x2 , x3 , … , xN )
ExposureVulnerability
Many processess, models, parameters.
Many steps, many uncertainties
Francesco Ballio
20
hydrologicalprocesses
damages
atmosfericprocesses
propagation(1D)
discharge: Q(t)
flooded area
water depth
water velocity
contaminants
Flood risk assessment: hazard
flood(2D)
Damage = f ( x1 , x2 , x3 , … , xN )
river geometrytown geometryvegetationbank and levee failuressediment transport…
origin / characteristics of uncertainties:
• natural system, complexity
• unsteadyness
Francesco Ballio
21
hydrologicalprocesses
damages
atmosfericprocesses
propagation(1D)
discharge: Q(t)
flooded area
water depth
water velocity
contaminants
Flood risk assessment: hazard
flood(2D)
We consider our models to be relatively robust from the
conceptual and mathematical perspectives. BUT:
• Available maps mostly come from 1D stationary
calculations
• All inputs but discharge are treated as deterministic
variables (often considered as null!)
• Uncertainties more or less subjectively embedded in safety
factors.
Francesco BallioCourtesy of Claudio Margottini,
ISPRA
Case study: hazard
Francesco Ballio
23Case study: hazard
event
discharge as
for an
estimated
return period
T=100 years
Francesco Ballio
Study mandated by the Orvieto Municipality to the professional consultant BETA Studio from Padova. Source: BETA Studio srl, S.
Nicolò, PD, Analisi idraulica e idrologica della piena del fiume Paglia nelle zone di Orvieto Scalo e Ciconia e scenario di
esondabilità: implicazioni per il sistema delle infrastrutture e dei trasporti, Ottobre 2013.
Case study: hazard
Francesco Ballio
Study mandated by the Orvieto Municipality to the professional consultant BETA Studio from Padova. Source: BETA Studio srl, S.
Nicolò, PD, Analisi idraulica e idrologica della piena del fiume Paglia nelle zone di Orvieto Scalo e Ciconia e scenario di
esondabilità: implicazioni per il sistema delle infrastrutture e dei trasporti, Ottobre 2013.
Reasons for discrepancies:
• singularities (1D vs.2D modelling)
• neglected / simplified parameters and
processes (sediment transport)
but: ex-post!
Francesco Ballio
26Flood risk assessment: exposure + vulnerability ���� damages
hydrologicalprocesses
atmosfericprocesses
propagation(1D)
flood(2D)
damageseffects
Damage = f ( x1 , x2 , x3 , … , xN )
ExposureVulnerability
exposure: what is inside the affected area?
vulnerability: how much of it will be damaged?
physical damage
value
Francesco Ballio
27
damage modelsflooded area
water depth
water velocity
contaminants
flood
(2D)
residential buildings
system
parameters
industrial & commercial activities
agriculture sector
infrastructures
public items
emergency costs
people
environmental and cultural herit.
Flood risk assessment: exposure + vulnerability ���� damages
no more chain, cluster
hazard (in)dependent?
Francesco Ballio
28
damage models
Flood risk assessment: exposure + vulnerability
flooded area
water depth
water velocity
contaminants
flood
(2D)
residential buildings
system
parameters
industrial & commercial activities
agriculture sector
infrastructures
public items
emergency costs
people
environmental and cultural H.
Net capital stock
VULNERABILITY MAP
(spatial distribution
of land use classes)
Conversion table
Overlapping/IntersectionLifelines and
strategic /pubblic
facilities map
Hazardous
installations map
Cultural/Env.
heritage map
Census block
map
CORINNE map
Monetary value
estimation-
other lifelines
Monetary value estimation-
pubblic/strategic facilities
Monetary value estimation-
cultural/environmental goods
Monetary value
estimation-
hazardous installation
….
Market value
Building areas
Net capital stock
Monetary value
estimation -
settlements
Monetary value
estimation-
industry
Monetary value
estimation-
wild areas
Exposure map (spatial
distribution of high
vulnerable elements)
Monetary value
estimation-
high vulnerable areas
…
Monetary value
estimation-
roads/railways
EXPOSURE MAP
(spatial distribution of
monetary value)
Calculation of
innundation depth (h)
HAZARDFlood profile
DTM
EXPOSURE/VULNERABILITY
Damage curves-
settlements
Direct tangible damage
Damage curves-industry
Damage curves-
agriculture
…
Damage
model
(v=1)
..
…
…
…
…
…
…
Indirect tangible damage Intangible damage
CombinationSignificance
TOTAL DAMAGE map
FLOOD HAZARD MAP
(spatial distribution of h)
FLOOD HAZARD MAP
(spatial distribution of h)
FLOOD HAZARD MAP
(spatial distribution of h)
FLOOD HAZARD MAP
(spatial distribution of h)
RISK
Estimate of population
at risk
Population
density
People
at risk
Flooded area
Monetary value
estimation-
industry
Production units
Production units
Monetary value
(struct. & cont.)
Monetary value
(struct. & cont.)
Monetary value
(struct. & cont.)
Damage
(struct. & cont.)
Damage
(struct. & cont.)
Damage
(struct. & cont.)
Affected
people
PoliMi procedure
Flood-IMPAT
Integrated Meso-scale
Procedure to Assess Territorial
flood risk
Francesco Ballio
29Case study: damages
agriculture
cars (parking)
houses
industries
highway
railway (station)
Francesco Ballio
30Flood risk assessment: damages - buildings
Location and dimension of buildings from
Cadastre
Value of building structure from Real Estate
and Property Price Database (OMI)
Value of contents: 7.5% � 25.5% of the
reference market value of building structures
(low-cost buildings � luxury buildings)
Francesco Ballio
31
Indicator Description
a) Location Hazard level depends on building location
b) Type of useContents value (and, consequently, damage) depends on buildings’ use (e.g. residential,
commercial, public service, etc.)
c) Level of maintenance Well maintained buildings better face the impacts of floods than crumbling
d) Age Age is usually linked to the level of maintenance
e) MaterialsSome materials (like concrete and masonry) are more resistant to the flood impacts than
others (e.g. timber, plasterboard, etc.)
f) Number of storeys The presence of more than one storey allows people to move contents to upper floors
g) Presence of
basementBasements can be flooded also in case of minor events (small water depth)
h) Number of openings
at street levelOpenings at street level make water to easily enter the building
i) Height from street
levelIf ground floor is higher than street level water is hindered to enter the building
l) Presence of vulnerable
equipmentsIf vulnerable equipments are present in more flood prone floors than damage can be higher
Flood risk assessment: damages - buildings
Francesco Ballio
32Case study: damages - buildings
0,0
0,2
0,4
0,6
0,8
1,0
1,2
0 2 4 6 8 10 12 14
DA
MA
GE
[-]
WATER DEPTH [m]
0,00
0,15
0,30
0,45
0,60
0,75
0,90
0 0,5 1 1,5 2 2,5 3
DA
MA
GE
[-]
WATER DEPTH [m]
M€
Observed damage 0.56
Estimated_SM 0.84
Estimated_FLEMO_ps 0.42
one family
detached
multifamily
umbria data
low rise
intermediate
high rise
Standard Method(Ministerie van Verkeer en Waterstaat, Holland)
FLEMO_ps(Thieken et al., 2008)
Francesco Ballio
33Case study: damages - buildings
0,0
0,2
0,4
0,6
0,8
1,0
1,2
0 2 4 6 8 10 12 14
DA
MA
GE
[-]
WATER DEPTH [m]
0,00
0,15
0,30
0,45
0,60
0,75
0,90
0 0,5 1 1,5 2 2,5 3
DA
MA
GE
[-]
WATER DEPTH [m]
M€
Observed damage 0.56
Estimated_SM 0.84
Estimated_FLEMO_ps 0.42
one family
detached
multifamily
umbria data
low rise
intermediate
high rise
Standard Method(Ministerie van Verkeer en Waterstaat, Holland)
FLEMO_ps(Thieken et al., 2008)
h
da
ma
ge
%
Unresolved features are embedded in the pdf. Calibration needed!
to be discussed:
• "richness" of the model: how many parameters
it considers
• scale: object, areal (averaged)
• uncertainties (referred to scale)
Francesco Ballio
34Flood risk assessment: damages – industrial activities
Rhein atlas(International commission for the protection of the Rhine)
stru
cture
content
Francesco Ballio
35Case study: damages – industrial activities
Damage to
Businesses
[M€]
Estimated
damages26,5
Observed
damages28,6
The monetary value of industry
land use class is calculated
from the knowledge of (i) the
net capital stock per
production unit and (ii) the
number of production units per
census block, both supplied by
ISTAT (subdivided by
structures and contents). The
net capital stock is differently
calculated (at national level)
for the several classes of
industrial activities as defined
by ATECO.
Francesco Ballio
36Case study: damages, overall results
19%
2%
23%42%
11%
2%
First aid
Cultural Heritage
Infrastructure
Industry
Agricolture
Residential
Umbria 2012, whole region
Francesco Ballio
37Flood risk assessment: what for? (discussion)
There is no universal / general structure for (flood) risk assessment.
Models, i.e.:
• their structure
• their scale
• their comprehesiveness
• their statistic vs. deterministic balance
• their accuracy (calibration / validation on data!)
• their …
can differ significantly from each other depending on the purpouse of
the assessment. (what for?)
back to the first slide
Francesco Ballio
Risk assessment: what for?
• land use planning (say, construction permission)
• design mitigation works (river training)
• emergency management (contingency plans)
• insurance costs
• …
… cost - benefit analysis
Conclusions
• complexity of the problem
• lack of knowledge on the damage side
• role of uncertainty / stochastic variables
• the risk of (over)simplification
� no ONE solution (what for?)
