up-nhrc ondoy study

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A PreliminaryEngineering Analysis of the

Marikina River Basin Flood ofSeptember 26, 2009

Learning Lessons, Carrying Onin the Wake of Storm Ondoy (Ketsana)

UP National Hydraulic Research Center

October 2, 2009


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Contents

A. Description of the Marikina River Basin

B. Hydrologic model of the river basinC. Interpretation of the peak rainfall, peak flood

discharge, and peak water level

D. Hydraulic model of the channels and floodplains

E. Recommendations1. Monitoring, forecasting, and early warning

2. Information dissemination

3. Decision-support system

4. Immediate response and preparation

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Part A:

Description of theMarikina River Basin

The NHRC, with the Institute of Civil Engineering at the College of

Engineering of UP Diliman, had used the SWATCH software and the UNET

software for previous studies of the Marikina River Basin and other Metro Manila

river basins for DENR, DPWH, and LLDA until 2005.

The existing SWATCH hydrologic model of the Marikina River Basinencompassed the river system from the mountains down to the Sto. Nio station.

The existing UNET hydraulic model covered each channel & its two overbanks.

Steep slopes characterize the upper catchment of the Marikina River Basin.

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Marikina River Basin

For one major tributary basin,

the Marikina River Basin(535 sq. km. drainage area)in the northeast, the only outletis through Pasig River,to Manila Bay in the west;

and partly through the MangahanFloodway diversion intoone extensive lake region,the Laguna de Bay Basin (withtotal basin area of 3,229 sq.km.)in the southeast.

MarikinaRiver

Pasig River

Laguna

de Bay

ManilaBay

Source of composite: UP NHRC3


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Metro-Manila Rivers and River-Basin Areas

Name of River Basins (RB) Drainage Area(sq.km.)

Marikina River Basin 535Mangahan Floodway-Taytay RB 63Taguig-Napindan RB 45

Meycauayan RB 169Obando-Malabon-Navotas Estuary 35

Novaliches Reservoir-Tullahan RB 72San Juan RB 94Pasig River Basin (north and south) 91

Paraaque-Las-Pias RBs 73Zapote-Bacoor-Imus RBs 168 Source: UP NHRC

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Top: Marikina River @Wawa Dam at Montalban gorge

(as seen in the early 1990s).

Left:Along Marikina River,

the towns / cities ofRodriguez (Montalban),San Mateo,Marikina &Pasig.

Source of composite:

UP NHRC5


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(Badilla 2008)

Elevations at Upper Marikina River Basin

Highest

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Elevations along Marikina River

Source: UP NHRC

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Part B:

Hydrologic model of theMarikina River Basin

Hourly rainfall data at stations within the river basin would be needed. The reported rainfall of 448 mm in 12 hours, converted into hourly rainfall, was

used in prelim. SWATCH model with an applied area reduction factor of 0.6. The

peak rainfall occurred around 11AM on Sept. 26, 2009.

The prelim. SWATCH computation indicated peak flood discharge at Sto. Niostation of abt. 5,770 cu.m./s around 12 noon on Sept. 26, 2009.

30-45 minute extreme warning, or even longer, could be enabled by proper

monitoring and simulation such as demonstrated in this preliminary modeling.

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Tabak

Bosoboso

Pasig

Science Garden

101

102

103

104

105

106107

108

109110

111

112

113

114

115

116

117

118

119 120

121122

123124

125126

127

128

129

130

131

132133

134135

136

137138

139

140

141

142

143

144

145

146

147

148

149

150

151152

153

154

155

156

157

158

159

160

161

162

163164

165166

167

168169

170

171

172

173

174

175

176177

178

179

180181182

183

184

Rainfall Stations

Rivers/Tributaries

Sub-Basin Divides

Marikina River Basin Boundary

LEGEND

Marikina River Basin

Sto. Nino Gaging Station

Sto. NinoGaging Station

121 00'o

14 50'o

121 00'o

14 35'o121 20'o

14 35'o

121 20'o

14 50'o

Rosario Weir

Rosario Weir

NORTH

Marikina River Basin Delineation

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The detailed river network of Marikina River Basin above Sto. Nio(DA=535 sq.km.): the basis of the UP NHRC SWATCH physics-based

distributed (rainfall-runoff) hydrologic model. Source: UP NHRC10


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Model Components: rainfall interception and retention storage

infiltration excess rainfall soil moisture storage in the root zone evapotranspiration interflow storage and discharge

groundwater recharge flow stream-aquifer return flow overland flow channel flow

Method of Solution: analytic and semi-analytic

methods with the use of discretekernels

Watershed discretization in SWATCH model showing overland flowplanes and river reaches.

watershed discretization showingoverland flow planes and riverreaches

each overland flow plane hasunique hydrologic and hydraulicproperties

!"# $

11 Source: UP NHRC


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(PAGASA)

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Wind Directionand Wind Speed

Hourly Rainfal, Average Pressure and Winds

in Manila Observatory (26 Sep 2009)

0

10

20

3040

50

60

70

12 AM 3 AM 6 AM 9 AM 12 PM 3 PM 6 PM 9 PM

Time (pht)

Ra

in(m

m)

985

990

995

1000

1005

Pressure

(hPa

)

Rain

Barometric Pressure

Highest rainfall about 60 mm/hr at Manila Obs. was measured bet. 10 AM and 11 AM. Higher rainfall might have been measured at other stations. Hourly rainfall data at stations within the river basin would be needed.

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Sept. 26, 2009 peak flood discharge of Marikina River @ Sto. Nio.

Hourly rainfall (mm/hr) @ Science Garden, QCStation, converted based on 448 mm in 12 hours(used in prelim. SWATCH hydrologic model withapplied area reduction factor = 0.6.)

Max hourly rainfall abt 90 mm/hr at 11AM.Peak flood discharge computed 5,770 cu.m./s at 12NN

Source of prelim. computation:UP NHRC

Level of 30-yr design-basis flood

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Part C:

Interpretation of the peak rainfall,flood discharge, and water level

The reported rainfall of 448 mm in 12 hours corresponded with extreme

rainfall with a return period of 180 years.

The preliminary computed peak flood discharge of 5,770 cu.m./s had an

estimated return period of more than 100 years.

For 4 hrs, the computed flood exceeded the 30-yr flood that is currently the

design basis for the Pasig-Marikina River Channel Improvement Project.

The computed rise of water level by as much as 8 meters matched with some

observed markers of flood level at Marikina.

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Highlights of the Hydrologic Design Parameters of Pasig-Marikina River Channel Impr. Proj.

Historical Annual Maximum

Discharge of Marikina River

at Sto Nino, Marikina

Year Max. Discharge, m3/s

1986 2650 *

1970 2464

1959 2072

1977 2051

1966 2036

2000 1895

1998 1680

1995 1676

1999 1642

1967 1609

etc.

Probable Annual Max. Discharge of Marikina

River at Sto Nino station (by Log Normal Prob.

Dist. and Flood Runoff Model)

Return Max. Discharge, m3/s

period Existing (1997) Future (2020)

(years) Land Use Land Use

Sto Nino Sto Nino Rosario

2 1350 1470 1480

5 1870 2020 2000

10 2210 2350 2320

20 2550 2740 2720

30 2740 2900 2890

(design flood)

50 2980 3120 3070

100 3310 3430 3440

The 20-year flood of 2,550 m3/s was exceeded in 1986; however the 30-year design-basis flood of 2,740 m3/s was not yet experienced in the42-year period of record, 1958-2000.

The 2009 flood was greater than a 100-year flood.

Source: UP NHRC16


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The 2009 rainfall correspondedto 180-year return period.

17 Source: UP NHRC


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The 2009 flood corresponded toabout 180-year return period.

18 Source: UP NHRC


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Computation of MAXIMUM RIVER WATER LEVEL

Using the published DPWH-JICADischarge Rating Curves (March 2002)

in the case of Marikina River at Sto Nio (DA = 535 sq.km.):Q = 17.01 (H 0.00)^1.85 for H < 5.33 metersQ = 0.20 (H 0.00)^4.49 for H > 5.33 meterswhich relates river gage height, H (meters),

to flow discharge, Q (cu.m./sec), by regression of historical data -

then the Peak Flood Flow = 5,770 cu.m./seccomputed by the SWATCH hydrologic modelcorresponds to a gage height of H = 9.8 meters,

which means that starting from an initially low H = 1 to 2 meters,the gage height (river water level) can rise by about 8 meters.

these computations matched with the observed markers ofmaximum flood water levels on 26 Sept. 2009 relative to the low banks.

Flood discharge Water level

19

Source: UP NHRC


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8 meters high5 meters high

Marikina Riverbank

9/28/2009.

Downstream view of Rosario Weir

along Marikina River.

Water level markers

20

Source of composite:UP NHRC


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Part D:

Hydraulic model of the riverchannels and floodplains

The UNET model considered the network of channels and adjoining floodplains,

from Sto Nino, to Napindan at Taguig, to Marikina River, to Pasig River down to

Del Pan Bridge at mouth of Manila Bay, including the vicinity of Provident Village.

Simulation could include such interior conditions as: bridges, culverts, gate

spillways, weirs, rating curves, levees, pumping stations, and channel constrictions.

Using the prelim. SWATCH flood discharge at Sto. Nio station as input, theUNET model computed water level rises of 5 meters or 8 meters which matched

with observed flood levels at several locations in Marikina.

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Sept. 26, 2009 peak flood discharge of Marikina River @ Sto. Nio.

Hourly rainfall (mm/hr) @ Science Garden, QCStation, converted based on 448 mm in 12 hours(used in prelim. SWATCH hydrologic model withapplied area reduction factor = 0.6.)Max hourly rainfall abt 90 mm/hr at 11AM.

Peak flood discharge computed 5,770 cu.m./s at 12NN

Source of prelim. computation:UP NHRC

Level of 30-yr design-basis flood

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River constrictionRiver constrictionexampleexample

22

Source ofcomposite:UP NHRC


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MANILA

BAY

PASIG RIVER CHANNEL IMPROVEMENT

PASIG RIVER

SANJ

UANR

IVER

MCGS

ROSARIO WEIR

MANGAHAN

FLOODWAY

LAG

UNA

LAKE

NAPINDANRIVER

LAKESHORE DIKE

SPILLWAY

PARA

AQUE

MARIKIN

AR

IVER

NHCS

500 cumecs

2400cumecs

2900

cumecs

UPPER

MARIKINARIVE

R

CHANNE

LIM

PROVE

MEN

T

LOWE

RMARIKIN

ARIVER

CHANNE

LIMPROVEMENT

MARCOS BRIDGE

MARIKINA BRIDGE

MANALO BRIDGE

LAMBINGAN BRIDGE

1200 cumecs

MAINT. BRIDGE

RODRIGUEZ BRIDGE

Schematic of Modeled Area

23Source of composite: UP NHRC


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282000 284000 286000 288000 290000 292000 294000 296000

1608000

1610000

1612000

1614000

1616000

1618000

Pasig-Marikina River System including Floodplains

Provident Village

SM Mall

Rosario Weir

Napindan

Manila

Bay

Santo Nino

24

Source:UP NHRC


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UNET is an unsteady flow, quasi, two-dimensional modelin that the network of channels is represented by

interconnected one-dimensional channel reaches andeach reach is composed of several cross sections withdistinct main channel flow and floodplain area.

Simulate interior boundary conditions such as:

bridges culverts gate spillways weirs

rating curves levees pumping stations

UNET : River and Floodplain HydraulicsUNET : River and Floodplain Hydraulics

(U.S. Army Corps of Engineers)(U.S. Army Corps of Engineers)

25Source: UP NHRC


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0.0 4.0 8.0 12.0 16.0 20.0 24.0 28.0 32.0 36.0

Distance, (km)

10.012.014.016.018.020.0

22.024.0

Eleva

tion(m

)

Typhoon Ondoy 12:00 Hrs: Water Surface, Discharge and Velocity ProfilesPasig-Marikina River (Manila Bay at km0.0 - Sto Nino at km33.7)

0.0 4.0 8.0 12.0 16.0 20.0 24.0 28.0 32.0 36.0Distance (km)

1000

2000

3000

4000

5000

6000

Disch

arge

(CMS)

0.0 4.0 8.0 12.0 16.0 20.0 24.0 28.0 32.0 36.0Distance (km)

0.0

1.0

2.0

3.0

4.0

5.0

6.0

Ve

loc

ity

(m/s)

Flood water elevation

26

Source: UP NHRC


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!

"

#$% $ & '& ( )* ! !

+*

!

), ,!!

(-%

RightRight overbankoverbank

LeftLeft overbankoverbank

Flood water elevation

Ground elevation

27

Source: UP NHRC


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28

Source of composite: UP NHRC


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29

Flood inundated areasaccording to computersimulations by UP NHRC


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Part E:

Recommendations Monitoring, forecasting, and early warning. With advances in field

instrumentations, geomatics, information & communication technologies, and

engineering simulations, prior warnings may be enabled.

Information dissemination. Geographic-information-system (GIS)-based datamay be catalogued, updated, processed, and relayed effectively to ground units

and/or to mass media outlets.

Decision-support system. The same technologies may be used for medium-term

and long-term studies and models for governance, planning, and engineering toreduce exposure and vulnerability to a multitude of natural hazards.

Immediate response and preparation. Infrastructures may have to be

reengineered to withstand greater hazards; communities may have to be

reorganized to operate under extreme catastrophic conditions.

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