Module 2_Hydromet Hazards 3

7/29/2019 Module 2_Hydromet Hazards 3

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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_Orleans


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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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HIGHMODLOW

HIGHMODLOW

HIGH

MOD

LOW

HIGHMODLOW

Mouth of River (Input) Rainfall

(Output) Discharge

Tides

SEA

WATERSHED


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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


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



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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

Module 2_Hydromet Hazards 3

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