The document discusses flood hazard mapping using FLO-2D software. It defines hazard, vulnerability, and risk, explaining that risk is a function of hazard and vulnerability. It describes how flood hazard depends on depth, velocity, and frequency in different countries. The US considers hazard based on depth and velocity for adults, cars, and houses. FLO-2D can model flood scenarios of different return periods and map hazard levels based on intensity and return period. A case study in Venezuela applied this process after deadly flooding and debris flows.

1. Flood Hazard Mapping
Reinaldo Garcia, PhD

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Outline
• Hazard, Vulnerability and
Risk
• FLO-2D Hazard Mapping
tool

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Hazard ≠ Risk
Hazard
•Related to an event that poses a
danger
Vulnerability
•Susceptibility to specific hazard
Risk
•Probability of suffering harm or loss

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Hazard ≠ Risk
Risk = Hazard ∩ Vulnerability
For specific hazard!!!

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Sacramento

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Hazard Zones for Flooding
•Hazard Intensity
•USA: f(h)
•Austria: f(h, v2/2g)
•Switzerland: f(h, v × h)
•Flood hazard depends on
Depth
Velocity
Frequency of the hazardous event

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Hazard in the U.S.A.
• The U.S. Bureau of Reclamation (1988) also
identifies hazard as a combination of depth and
velocity and differentiates these for adults, cars,
and houses as shown in the following figures.
USBR. 1988. Downstream Hazard Classification
Guidelines. ACER Technical Memorandum No.
11.

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Hazard in the U.S.A.
Flood Hazard for Adults
U.S. Bureau of Reclamation(USBR 1988).

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Flood Hazard for Houses
U.S. Bureau of Reclamation(USBR 1988).

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• Swiss and Austrian standards (see OFEE et al. 1997,
Fiebiger 1997).
• Three zones identify the potential hazard in a location.
• Flood hazard is defined as a discrete combined function
of the event intensity (severity of the event) and return
period (frequency).
• The intensity of the event is a function of the flow depth
and velocity.
• Frequency of the event is based on the simulation of 3
scenarios, e.g. 10, 100 and 500 years return period
FLO-2D Hazard Mapping

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Spreadsheet
H
2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
1.9 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
1.8 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
1.7 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
1.6 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
1.5 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
1.4 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
1.3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
1.2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
1.1 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
0.9 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
0.8 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
0.7 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
0.6 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3
0.5 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3
0.4 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
0.3 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
0.2 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
0.1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
VxH 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.4 1.45 1.5 1.55 1.6 1.65 1.7 1.75 1.8 1.85 1.9 1.95 2 2.05 2.1 2.15

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Hazard Levels

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Hazard map legend
Hazard
level
Map color Legend
High Red
People are in danger both inside and
outside of structures. Buildings
are in danger of being destroyed.
Medium Orange
People are in danger outside or
structures. Buildings may suffer
damage or possible destruction
depending on construction
materials.
Low Yellow
Danger to people is low. Buildings
may suffer limited damage, but
flooding or sedimentation may
affect structures.

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Hazard mapping workflow
• Apply hydrological model: Inflow hydrographs
• Apply FLO-2D model to obtain maximum
velocities and maximum depth maps for mud
floods of three return periods (10, 100 and 500
years or other)
• Determine intensity maps for these three events
based on the established criteria
• Determine hazard levels from intensity maps
and event return period

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Case study
• Debris Flow and Flooding.
• Northern Venezuela.
• December 1999.
• 20 alluvial fans affected.
• ~15.000 people died/disappeared .
• US $5+ billion in losses.

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Macuto River in the alluvial fan, Sept. 2001.

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Rainfall data
• 911 mm /35.9 in from 14th to 16th
• 1207 mm/47.5 in December 1999
• 250 year event
•Annual average 523 mm /20.6 in
•Annual maximum 961 mm/37.8 in

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RESULTS FOR 10 YEAR EVENT

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RESULTS FOR 100 YEAR EVENT

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RESULTS FOR 500 YEAR EVENT

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Next:
Damage
Assessment