HAZARD MAPPING FOR FLOODING AND MUDDEBRIS FLOWS

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HAZARD MAPPING FOR FLOODING AND MUD/DEBRIS
FLOWS Reinaldo GARCÍA
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Outline

• Risk and Hazard
• Brief review of flood hazard assessment criteria
• FLO-2D Hazard delineation method
• Case study 1999 floods in Venezuela
• Hazard delineation tool
• Damage assessment tool

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Hazard ? Risk

• Hazard
• a potentially damaging physical event,
  phenomenon or human activity that may cause the
  loss of life or injury, property damage, social
  and economic disruption or environmental
  degradation (UN-USDR, 2004).

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Hazard ? Risk

• Risk
• is defined as the probability of harmful
  consequences, or expected losses (deaths,
  injuries, property, livelihoods, economic
  activity disrupted or environment damaged)
  resulting from interactions between natural or
  human-induced hazards and vulnerable conditions
  (UN-USDR, 2004.

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Hazard ? Risk

• Risk
• Risk Hazards Vulnerability
• Many people say Risk, but they mean Hazard

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Hazard Zones for Flooding

• Hazard Intensity
• FEMA f(h)
• Austria f(h, v2/2g)
• Switzerland f(h, v h)
• Flood hazard depends on
• Depth
• Velocity
• Event frequency

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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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Flood Hazard for Adults U.S. Bureau of
Reclamation (USBR 1988).
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Flood Hazard for Cars 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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FLO-2D Hazard delineation criteria

• Based on 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.
• Hazard maps simpler to understand by planners,
  managers, and end users.

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Event intensities f(h, v)
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Spreadsheet
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Proposed methodology
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Definition of hazard level
.
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Methodology for hazard mapping

• Apply hydrological model Inflow hydrographs
• Estimate total sediment volume
• 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 potential 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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Location
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Video
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Macuto, Edo. Vargas.
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Macuto River in the alluvial fan, Sept. 2001.
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Macuto, aguas arriba de toma.
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• 911 mm /35.9 in from 14th to 16th
• 1207 mm/47.5 in first 17 days of December.
• 250-500 year event

• Annual average of 523 mm /20.6 in
• Annual maximum of 961 mm/37.8 in (1951)

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• Approximately 15 x 106 m3 sediment.

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• Galipán Experimental Watershed (Macuto)
• Area 14 km2
• Highest elevation 2,300 m
• Alluvial fan slope 6
• Main stream length8.7 km
• Main stream slope 52

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Macuto, 1998
Macuto, Dec. 1999
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Picacho Galpán
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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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Ars longa,vita brevis