module 2_hydromet hazards 1

7/29/2019 Module 2_Hydromet Hazards 1

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SUSAN R. ESPINUEVA

HYDRO-METEOROLOGY DIVISION,

PAGASA, DOST

Department of Science and Technolog y

Phi l ippine Atmosph er ic, Geophysical and A stronomical Services Administ rat ion

Hazard 102:Hydro-meteorological Hazards (Part 1) - Intro

Training on Trainers on DRR/CCA for Local Partners8 January 2013, Tagaytay City

Project on Enabling Cities in Cagayan de Oro and Iligan to Cope

with 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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Outline of Presentation

1. Background

2. The Hydrologic Cycle, Runoff Process, River

System

3. Types and causes of flooding, flood mitigation

measures, some examples of extreme flood4. Flood hazard and risk mapping

5. Flood forecasting and warning system

6. Challenges, opportunities and WAY FORWARD
http://h/wiki/New_Orleans


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Nature of hazards in the PH

According to any criteria, the Philippines is an extremely

dangerous place to inhabit.

One of the most comprehensive records on the

occurrence of recent natural hazards even advised that

the archipelago has experienced more disasters thanany other country in the world since 1900.- Centre for Research on the Epidemiology of Disasters, Universit Catholique de

Louvain, Brussels (hereafter CRED) EM-DAT: The OFDA/CRED International

Disaster Database.

Residents of southern Luzon were likely to face a majortyphoon once every 5 to 6 years in the 18th century and

once every four to five years in the 19th century.- Rantucci, Geological Disasters in the Philippines, 27; Archive of the Manila

Observatory, Manila (hereafter AMO):


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Background

Geographical Location of the PH

The PH cl imate is inf lu encedby the complex interact ions

of var ious factors such as:

Philippine Geographyand Topography

Linear systems Principal Air Streams

Semi-permanentcyclones and anti-cyclones

Tropical Cyclones

Ocean currents


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Background

Physiographic features of the PH

Associated hazard: Flashfloods

EFFECT OF TOPOGRAPHY

Topographic Map of PH


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Hydromet hazards in the PH

1. Floods/flash floods

2. Storm surges

3. Rainfall induced landslides4. Drought


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Background

The Water (Hydrologic) Cycle


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The Runoff process

That portion of rainfall percolating to lower layers becomes part ofthe groundwater. Groundwater flow to a stream or river is termed

baseflow - supports streamflow during non-storm periods.

A critical issue is how to determine exactly what comprises runoff.

One component isthe water visiblyflowing across theground surface. As

water infiltrates,some water willflow just below thesurface (interflow,or subsurface

stormflow).


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The Runoff process

Runoff Process is defined as the portion of rainfall and/or

irrigation water that runs over the soil surface toward the

stream rather than infiltrating into the soil. It is sometimes

called surface runoff.


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The Runoff process

Runoff is that portion of rainfall that does not infiltrate intothe soil. In the case of a paved area, the expected runoff

would equal the amount of rainfall minus evaporation andany small amount of surface storage.


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The Runoff process

The accounting budget approach for hydrology is expressed

as:

Inflow (I) Outflow (O) = +/- Change in Storage (S)

Or

I O = +/- S

(Continuity Equation/Conservation of mass)

Surface water storage and distribution occurs in lakes,

ponds, rivers, and streams and accounts for less than 0.01%

of the earth's water.

Groundwater - occurs in the aquifer, a region beneath the

earth's surface composed of unconsolidated rock and soil

particles. Less than 1% of the earth's total water supply is

stored as groundwater or soil moisture.


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The Runoff process

Springs are almost

completely fed bygroundwater sources.If enoughgroundwater is taken

out of storage and thelocal water table islowered, baseflow,the water in a streamoccurring during non-

storm or dry periods,will decrease andsprings may disappear.


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The Runoff process

The amount of water that infiltrated during an earlier stormincreases the current soil moisture. This means that the soilcannot absorb as much water as before resulting in a decreased

infiltration rate and more surface runoff from the later storm.

As the soilbecomes

saturated, lessinfiltration willtake place. Foridentical storms,

the amount ofstorm runoff willvary depending onthe soil moistureconditions.


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The Runoff process

A graph of streamflow is called

a hydrograph.

The shape of the hydrograph isinfluenced by the storm andwatershed characteristics.

Storm factors include amount,duration, intensity, and arealextent of precipitation.

Watershed factors include basin size, shape, overall basinslope, topography, soil & vegetation, channel network anddrainage pattern, land use, and soil moisture conditions at

the time of the storm.

D fi iti Ri b i


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Definition River basin

The soil water that travels through various processes reaches the riverat various time scales. Baseflow takes months to reach the streamand sustains the river during its low or normal flow. An accounting ofthe soil water and surface runoff in order to forecast flood is usuallydone on a river basin or watershed. A basin is defined as a drainage

area of a stream, river or lake.

A river basin isthe area within

the basin divide(blue outline),and drains thesurface runoffand riverdischarge (greenlines) of acontiguous area .

Ri t


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River system

Source: JICA TCP: Strengthening Floof Forecasting and Warning System for Dam Operation, Nov 2012


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Longitudinal profile of Agno River (Upstream)

Agno Riverup to the Agno-Tarlac confluence



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Longitudinal profile of Agno River (Upstream)

Agno Riverup to the Agno-Tarlac confluence



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River flow capacity

CabatuanTaotao River

Aur or a Br idge

Gamu

Aurora

San Mateo

CamarungayanKalabasa

Bagong-Tanza

San Andres

Bagong Sikat

Pulay

Lalog

Kalinga

Santor

Cataban

Banguero

Reina Mercedes

FuraoLenzon

San Roque

Bannor

Namipucan

Bolinao

Victoria

Villa Fugo

Apiat

Mapurok

San Roque

Sinamar Norte

Oscariz

50000 2500

Scale (km)

N

S

EW

Relocation Luna Br idge

San Roque Over f l ow Br idge

MAGAT DamMARISDAM

Magat River

Cagayan River

Legend

City/Town

Barangay

Presumed Inundation Map in the Magat

River during Typhoon Emong in 2009



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River flow capacity

1,3

90m

Left Bank

El. 55.6 m

Right Bank

El. 56.4 m

El. 56.6 m

El. 58.4 m

River Flow



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River boundary

Water Code: Article 51

Preparatory Survey for Flood Risk Management Project

for Cagayan de Oro River (FRIMP-CDOR)


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River boundary: No building zone

Tropical Storm SendongDanger Zone (Prohibited

Area for buildingconstruction)




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River boundary: Alternatives



Option 1: Water Code (up to Highest Flood Level) & Topography

Reference: Previous M/P (along bank of low water channel)Option 2: Protection for residential area

Residential Area

Inundation at HWL


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River boundary



Present main issues

- DPWH had never invoked the Flood

Control Area based on the Water Code

- In spite of Article 56 of Water Code,river beds, sand bars are being developed.

- Local peoples are settled or come back

at danger zones within the River Area

1. Main Laws/Regulations/Orders

(1) RA10121: comprehensive and Integrated DRRM approach(2) Water Code: determination of easement, establish flood control area, etc.

(4) Local Government Code : All the LGUs have responsibility to deliver basicservices, including flood control facilities.

(5) Executive Orders by each related LGU : establishment of LDRRMCs in each LGU

A Challenge of enactment of No-build

Zone in Cagayan de Oro City

- Enactment of City Ordinance for No-

build Zone- Approval of Comprehensive Land Use

Plan, Including No-build Zone of CDO

City

After that, declaration of Flood Control

Area by DPWH will be needed.

2. Legal aspects related to River Boundary

River basins in the Philippines


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River basins in the Philippines

There are 421 principal river basins and twenty (20) of these areconsidered major river basins with catchment areas that are

1,400 km2

or more. The flood plains of major river basins arehighly susceptible to severe flooding.

Low-lyingagriculturally

developed andeconomicallyproductive landsalso frequentlydevastated byextreme floodingevents.

Major river basins Topographic map

module 2_hydromet hazards 1

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