Post on 14-Apr-2018
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SUSAN R. ESPINUEVAHYDRO-METEOROLOGY DIVISION,
PAGASA, DOST
Department of Science and Technolog y Phi l ipp ine Atmosph eric , Geophysica l and A st ronomical Serv ices Adminis t ra t ion
Hazard 102:Hydro-meteorological Hazards (Part 3)
Flood hazard & risk mapping
Training on Trainers on DRR/CCA for Local Partners8 January 2013, Tagaytay City
Project on Enabling Cities in Cagayan de Oro and Iligan to Copewith Climate Change (Project Climate Twin Phoenix)
http://www.google.com/imgres?imgurl=http://www.nidm.net/images/flood6.jpg&imgrefurl=http://www.nidm.net/flood5_ii.asp&h=317&w=498&sz=16&tbnid=xQsMwHR6MnYJ::&tbnh=83&tbnw=130&prev=/images?q=flood+disaster+pics&usg=__OxfdyzuXcEc7in4yM2hADUqjZi8=&sa=X&oi=image_result&resnum=2&ct=image&cd=1http://h/wiki/New_Orleans7/29/2019 Module 2_Hydromet Hazards 3
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Indicative Flood Hazard Maps
TC frequency
occurrence
Flood & storm
prone areas
Flood & landslide prone areas
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Definitions - HAZARD
Hazard is defined as the intrinsic property,characteristics, or condition of a material or system thathas the potential to cause harm.
In essence, hazard is a physical situation with a potentialfor human injury, damage to property, damage to theenvironment, or a combination thereof.
In DRR/CCA, natural hazard pertains to events arising
from geologic and/or hydro-meteorological processesthat have the potential of causing deaths, injuries and/or damage to property.
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Definitions - RISK
Risk , is defined as the likelihood of an adverse effect,direct or indirect, on human health and welfare.
Usually expressed as a combination of frequency, or probability, and the consequence of a specific hazardous
event, risk may be estimated from the records of suchconsequences as had been experienced before, given thesame or similar attendant conditions.
Sometimes, the expression of risk includes the severity of
damage or adverse result that could be in terms of fatality,or injury, or cost of property loss per unit of time. It shouldbe noted that there can be no risk without a hazard.
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Definitions - RISK
Mathematically, risk is expressed as:
Risk = co nsequence f requency /prob abi li ty o f occur rence
Alternately, natural risk can be presented conceptually using therisk triangle developed by Crichton: *
* Geosciences Australia,Natural Hazards in Australia:Identifying Risk AnalysisRequirements
Using this risk triangle, risk ismathematically expressed as the productof hazard, exposure and vulnerability:
Ris k = h azard exp os ur e vu ln erabilit y
Hazard refers to a single event or series of events which ischaracterized by a certain magnitude and likelihood of occurrence. Exposure refers to the elements that aresubject to the impact of a specific hazard (i.e., elements at r i sk ) such as houses on a floodplain. Vulnerabil i ty is thedegree to which the exposed elements will suffer a lossfrom the impact of a hazard.
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Agencies involved in hazard mapping
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Different approaches in flood hazard mapping
1. Past flood approach
2. Hydrologic approach
3. Hydraulic approach
4. Geomorphological approach
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Geomorphological approach
GeomorphologicalLandform analysis
Terrain mapping
Historical research/verification
Field mapping and
interviewsGIS processing
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Agencies involved in hazard mapping
HIGHMODLOW
HIGHMODLOW
HIGH
MOD
LOW
HIGHMODLOW
Mouth of River (Input) Rainfall
(Output) Discharge
Tides
SEA
WATERSHED
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Agencies involved in hazard mapping
PLAN VIEW
Alluvial Deposits (Floodplain)
River Moderate
High
Worst Case Scenario(Low Susceptibility)
CROSS SECTION VIEW
Watershed (river basin)
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Methodology
OBSERVATIONS AND ANALYSIS
A. Type of Flooding - determined based on geomorphic,hydrological analysis and field interviews:
River ine f loods - originating from channel overflow;
Coasta l f lood s - orig inating from the sea
Stagnat ion f lood s - depressions in the absence or insufficient outlets;
Sheet f lood s - originating from concentrated runoff on slopes with or without insufficient rills and gullies;and Flashf loods - high velocity flows confined in steepchannels mostly straight and V- shaped; also fromunderground river networks.
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Methodology
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Methodology
Google Earth SatelliteImage of the target areas.
Drainage analysis andinventory of the target
areas.
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Methodology
Tabletop flood hazardanalysis
Field validation of tabletopflood hazard analysis
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Methodology
B. Historical Flood DataDoes the area experienced flooding:
During the passage of Typhoons During the occurrence of heavy rains During high tides and big waves
OBSERVATIONS AND ANALYSIS
C.Frequency of FloodsHow frequent does flooding occur?
Frequent several times a year or at least once a year Less Frequent - at least once in 5 yrs Seldom- at least once in 10 yrs Very seldom- cannot measure
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Methodology
D.Depth of Floods High flood hazards - ranging from a few inches to a
maximum of 10 feet Moderate flood hazards - ranging from a few inches
to 4 feet Low flood hazard- ranging from a few inches to 2 feet Less likely to be flooded unobserved
OBSERVATIONS AND ANALYSIS
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Methodology
TYPE OF FLOODING HAZARD
A.Highly susceptible1. Morphology - Beach, estuary, marsh, swamp, swales,
mudflats, tidal flats, main channels, channeltributaries, lower terraces, paleo-channels, oxbows,lakes, sinkholes, back swamps, gullies, rills.
2. Frequency- Frequent to less frequent3. Depth - Varying (Maximum of 10 feet and over)
B. Moderately susceptible1. Morphology - Beach ridges, middle terraces, raisedsandbars, levees
2. Frequency - Less frequent to seldom3. Depth - Varying (Maximum of 4 feet )
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Methodology
TYPE OF FLOODING HAZARD
C. Low susceptible1. Morphology Foot slopes, hills, ridges2. Frequency - Seldom3. Depth - Varying (Maximum of foot)
D. Less Likely to be flooded1. Morphology - mountain tops, steep slopes2. Frequency - unobserved3. Depth unobserved
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Methodology
GIS ANALYSIS AND PROCESSING
A. Basemap Preparation The map sheets with1:50 000scale of the study area, acquiredfrom NAMRIA were scanned and
geo- referenced using ArcGIS 9.3- ArcMap-ArcInfo.
To eliminate the annotations andproduce a basemap with only thetopographic details, extraction bymask under the spatial analyst toolswas used.
The maps were then cropped andmosaiced to fit and produce onesingle basemap for study area.
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Methodology
B. Flood Hazard Maps
GIS ANALYSIS AND PROCESSING
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Flood Hazard Maps
Flood Hazard Maps using 1:10Kbase maps (output from theUNDP Ready Project byUNDP/AusAID)
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Provinces/Islands with 1:10K FHM
Project Province Municipality/city
AusAID/ UNDP 1. Antique San Jose, Hamtic,Sibalom & Belison
2. Bohol Guindolman, Anda,Candijay & Duero
3. Rizal Angono, Baras,Binangonan, Cardona,
Morong, Tanay &Taytay
4. Benguet Baguio City and LaTrinidad
5. Pampanga Angeles City
6. Cavite Tanza, Gen. Trias,Imus, Dasmarinas,Rosario, Noveleta,Kawit, & Bacoor
7. Iloilo Iloilo City, Oton, Pavia,Leganes & San Miguel
Project Province Municipality/City
8. Leyte Ormoc City9. Zambales Olongapo City
& Subic
10. IlocosSur
Vigan City
11. Laguna Calamba City
12. Surigaodel Sur
Tandag &Tago
13. Surigaodel Norte
Anaon &Mainit
14. Abra
15. Cagayan
16. Isabela Roxas
GGGI /CCC
17. SiargaoIsland
San Benito,Del Carmen,Pilar, SanIsidro
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Flood Hazard Maps
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Flood Hazard Maps
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Flood Hazard Maps
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Flood Hazard Maps
B. Flood Hazard Map of Siargao Island
Mosaic FloodHazard Map of
themunicipalitiesof San Benito,Del Carmen,San Isidro, and
Pilar of SiargaoIsland