2/23/2009

FLOOD/FLASHFLOOD HAZARD
MAPPING ACTIVITIESIN THEPHILIPPINES
Oskar D. Cruz
Flood Forecasting Branch
PAGASA--DOSTPAGASA
East and SoutheastAsia Regional Seminar on Flood Hazard
Mapping
February 1717-19, 2009
Shangrila Hotel, Metro Manila
Philippines

MANDATED AGENCIES• Phil. Atmospheric, Geophysical andAstronomical Services Administration(PAGASA)DOST
Mines and GeoGeo-sciences Bur. (MGB)
DENR1

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Completed Project Areas
1:50,000PAGASA-UNDP
PAGASAOCHAQUEZON PROVINCE.RealPAGASA-CARE PHIL.
PAGASAAurora Province. Dingalan.Infanta.General Nakar
PAGASA--LOCAL GOVERNMENTSPAGASA.QUEZON CITY.TAGUIG CITY.DAVAO CITY.BUTUAN CITY.ILOILO CITY.BATAAN

Target Project Areas
PAGASA-UNDP READY PROJECT• Leyte• Zambales• Ilocos Sur• Laguna• Pampanga• Iloilo• Cavite• Rizal• Benguet• Antique

1:10,000• Bohol• Aurora• Southern Leyte• Northern Samar• Zamboanga City
• Ilocos Norte• Zamboanga
Sibuguey• Nueva Viscaya• Agusan del Sur2

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Target Project Areas
PAGASA-Gov’t. of the Philippines(GOP)
1:10,000••••••••

Pangasinan
BulacanAgusan del Norte
Western Samar
Gen. Santos
Cam. NorteQuezon
Or. Mindoro• Aklan• Batanes• Zamboanga delNorte• Bukidnon• Davao• Mt. Province• Lanao del Sur• CebuInventory Map of FloodFloodprone areas in thePhilippines
Mines and GeoGeo-Sciences
Bur.
DENR

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Mines and GeoGeoSciences Bur. (MGB(MGBDER)
JICA assisted Proj.
Scale 1:50,000
236 quadrangles
165 completed(1:50,0000)
71 quadrangles
processing

Methodology for Geomorphological
Flood Hazard Mapping
Data Gathering•Remote sensing
data•Aerial photograph•Topographic map•Historical data onflood•Previous works

Tabletop Analysis•Stereophotoanalysis•Drainage
inventory/analysis•Geomorphologicalmapping units(TMU)

Preliminary Flood
Hazard Map

Field Verification/Mapping

Final Flood Hazard
Map4

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Methodology• Geomorphological
Landform analysis
Terrain mapping
Historical research/verification
Field mapping and interviews

Terrain mapping units (TMU)
The ordering of degree of susceptibility is subjective
and depends on the scale and expert judgement•

1st order= high susceptibility active
channel, backswamp, oxbow,
paleochannel, swales, mudflats, etc•

2nd order = mod susceptibility naturallevee, point bar, sandbar, lower
terrace, beach ridges,etc.

•3rd order = low susceptibility upperterrace, talus slope, etc.

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Rainfall records of Historical
Floods
YearMonthDay

Total Rainfall

Monthly
NormalvalueMax.
monthly
record24 hrreturnper.

6 hr

returnper.

num. of days ofant.rainfall

num. of rainydays in amonth

2000

January

29

728.2

1212.3

228.0

298.2

2325

1999

March

11446.7

913.5

174.4

2134.421261999

January

10728.2

1644.2

374.0

25

208.0

10

328181997

March

9446.7

669.9

236.4

5111.22131996

February

6516.3

983.2

250.6

5177.0514261993

February

5516.3

889.2

298.6

10182.056211992

December

17539.1

830.2

194.4

2126.022271990

March

7

446.7

678.8

287.6

5146.425231988

November

29389.9

517

173.8

2112.42125

1986

November

28

389.9

663.4

321.6

15307.2

505191986March

5446.7

786.8

190.6

2132.024261986

January

22728.21144.2

252.3

5245.01521301985

December

17539.1

539.2

226.8

2191.652211985

January1728.2

484.6

203.7

2158.5

21010

1982

January

30

728.2

1195.3

250.6

598.7

21528

1981

January

31728.2

1377.2248.95165.1

51029

1981

January

12728.2

1377.2315.910143.0

21929

1979

December

18539.1

564.8

151.7

2127.82

1

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Flood susceptibility vsgeomorphic units
PLAN VIEW
Watershed (river basin)

CROSS SECTION VIEW
Alluvial Deposits (Floodplain)
Worst Case Scenario(Low Susceptibility)
ModerateRiverHigh

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Flooding in Central Luzon, 30 Nov. 2004
(Unding, Violeta and Winnie)

Geomorphological Mapping Systemwith Sub-Units and Details72/23/2009

Stereophoto-Interpretation on aerial
photographDingalan town
airphoto
2005

Preliminary Interpretation
Flood/flashfloodHazard Map
2005 aerial photo
Approx scale:
1:25,000
Source: ICDAI

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Ortho Photomap of Angeles City andVicinity, Pampanga, 10k

Preliminary tabletop analysis

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Field verifications and mapping

Field Interviews10

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Output Maps

Output Maps11

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Infanta,, Quezon
Infanta

REINA Output Maps

Real, Quezon

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REINA Output Maps

Nakar,, Quezon
Nakar

CARE Output Maps

Dingalan,, Aurora
Dingalan13

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READY I Output Maps

Anaon,, Surigao Del Norte
Anaon

READY I Output Maps

Tandag,, Surigao Del Sur
Tandag14

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READY I Output Maps

Tago,, Surigao Del Sur
Tago

READY I Output Maps

Mainit,, Surigao Del Norte
Mainit15

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READY II Output Maps

Ormoc City, Leyte

READY II Output MapsOlongapo and Baretto Zambales

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READY II Output MapsOlongapo and Baretto Zambales

READY II Output Maps

Calamba, Laguna

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READY II Output Maps

Calamba, Laguna

READY II Output Maps

Vigan City, Ilocos Sur18

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READY II Output Maps

CaviteREADY II Output Maps

Cavite19

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READY II Output Maps

Angeles, Pampanga

READY II Output Maps

Angeles, Pampanga

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ACKNOWLEDGEMENTS• UNDP• US OCHA• AUSAID• JICA
JICA--ICHARM• CARE PHIL.

THANK YOUENDPAGASA-DOSTPAGASAFlood Forecasting Branchwww.pagasa.dost.gov.ph

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