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Dr Liongson discusses the effects of TS Ondoy
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UPCOE-ICE-NHRC Public Presentation
Typhoon Ondoy (Ketsana) and the Marikina River Flood
of September 26, 2009
Venue: Beta Epsilon Multi Media Hall, Melchor Hall, UPD
Time: 9:00-10:30 AM, Friday, October 2, 2009
PROGRAM
Opening Remarks (9:00-9:10 AM)
Dean Rowena Cristina Guevara
Presentations* (9:10 – 10:20 AM)
Typhoon Ondoy Rainfall Intensity-Duration-Frequency Statistics
Marikina River Basin Flood, Hydraulics and Issues
Proposed Multi-Hazard Risk Assessment & Capacity Building for Metro Manila
Flood Issues, Management and Climate Change
Open Forum (10:20 – 11:00 AM)
Closing
*Speakers include Dr. Leonardo Q. Liongson and Dr. Guillermo Q. Tabios III
of the UPCOE Institute of Civil Engineering
METRO-MANILA:
Meycauayan (until early 1980s)
Kamanava: Kalookan,
Malabon, Navotas, Valenzuela
Manila Quezon City, Marikina,
San Juan,
Mandaluyong, Pasig,
Makati, Pateros-
Pasay, Taguig,
Parañaque,
Las Piñas,
Muntinlupa.
Brief Background: the River Basins of Metro Manila.
Metro Manila -
is composed of 7 small highly
urbanized river sub-basins
(702 sq. km.) which drain
directly to Manila Bay,
and through Pasig River,
serves as the only outlet of
one major tributary basin,
the Marikina River Basin
(535 sq. km.) in the northeast,
and one extensive lake region,
the Laguna de Bay Basin with
21 tributary SBs : 2300 sq. km.
Lake area : 929 sq. km.
Total basin area: 3229 sq.km.
in the southeast.
Marikina
River
Pasig River
Laguna
de Bay
Manila
Bay
Top: Marikina River
@Wawa Dam at Montalban
gorge as seen in the
early 1990’s.
Left: The towns of
Rodriguez (Montalban),
San Mateo, Marikina & Pasig
along Marikina River.
Metro-Manila Rivers:
Name of River Basins Drainage Area (sq.km.)
Marikina RB 535
Mangahan Floodway-Taytay RB 63
Taguig-Napindan RB 45
Meycauayan RB 169
Obando-Malabon-Navotas Estuary 35
Novaliches Reservoir-Tullahan RB 72
San Juan RB 94
Pasig RB (north and south) 91
Parañaque-Las-Piñas RBs 73
Zapote-Bacoor-Imus RBs 168
Source: NHRC
The detailed river network of Marikina River Basin above Sto. Niño (DA=535 sq.km.):
the basis of the NHRC SWATCH physics-based distributed hydrological (rainfall-runoff) model .
(NHRC)
Marikina
River Basin
(535 sq.km.)
and the 21
sub-basins
& lake of the
Laguna de
Bay Basin
(3229 sq.km.)
(NHRC)
Marikina
River Basin
(535 sq.km.)
and the 21
sub-basins
& lake of the
Laguna de
Bay Basin
(3229 sq.km.)
(Wikipedia)
Marikina RB
Pasig RB
Mangahan
Floodway
(Badilla 2008)
(JICA)
(NHRC)
(NHRC)
Mean daily streamflow in Marikina River at Sto Niño in year 1990.
EFCOS: Effective Flood Control Operations System
(located in Metro-Manila & Rizal province)
• Aims to achieve an effective flood
control operation for Pasig-Marikina-
Laguna Lake Complex through
• real time rainfall and water level data
collection at the Rosario Master Control
Station via telemetry system;
• the effective use of the warning system
along Mangahan Floodway; and
• the multiplex communication system
among Rosario MCS, Napindan HCS,
DPWH Central Office and PAGASA Data
Information Center.
Effective Flood Control
Operating System (EFCOS)
of Metro Manila – was discontinued by MMDA.
The Mangahan Floodway
diverts floodwaters of
Marikina River to Laguna
de Bay.
The Napindan Hydraulic
Control Structure (NHCS)
regulates flow between
Pasig River and the lake
via the Napindan Channel
The navigation lock of the
NHCS allows water traffic
between Pasig River and
Laguna de Bay through the
Napindan Channel.
Track of TS Ketsana (Ondoy) –
from Joint Typhoon Warning Center (JTWC), US Navy
(PAGASA)
Flooding started fast at the SM North EDSA, Quezon City (Flickr).
Large runoff on pavements
and
underground floods in
the Ayala underpass, Makati (Flickr).
Inundation of the
Provident Village
in Marikina City
(Googlemap; Flickr).
Coping aboard fiberglass boats in Bay, Laguna (Flickr – IRRI).
Collapse of a wall
of the Mangahan Floodway
near Rosario Bridge, Pasig City.
(Googlemap; Flickr).
Property damage
(Flickr).
Suffering
and death
(Flickr).
And a safe passage.
(www.op.gov.ph
and Flickr)
8 meters high
5 meters high
Marikina Riverbank
9/28/2009.Downstream view of Rosario Weir
along Marikina River.
Preliminary Computations
SWATCH-computed
Peak Flood
Discharge = 5770 cu.m./s
of Marikina River
at Sto Niño
on 26 September 2009,
based on the
Point Hourly Rainfall
at Science Garden, QC
Synoptic Station with
applied area reduction
factor = 0.6
(NHRC)
• Rainfall Depth starting at 8:00 am, 26 September 2009:
6 hours: 347.5 mm
9 hours: 413.0
12 hours: 448.5
• Sliding Maximum Rainfall Depth:
6 hours: 381.5 mm
9 hours: 418.0
12 hours: 448.5
For Rainfall depth, P = 347.5 mm in D= 6 hours duration, its Return Period, T = 100 to 150 years.
• Based on the PAGASA web-published chart (below) of Science Garden station: P = function(T, D);
• also on the DPWH-JICA (March 2003) regression equation: P = D* A(T)/[C(T) + D]^b(T) based on PAGASA data.
Computation of MAXIMUM RIVER WATER LEVEL
• Using the published DPWH-JICA
Discharge Rating Curves (March 2002)
in the case of Marikina River at Sto Niño (DA = 535 sq.km.):
Q = 17.01 (H – 0.00)^1.85 for H < 5.33 meters
Q = 0.20 (H – 0.00)^4.49 for H > 5.33 meters
which relates river gage height, H (meters),
to flow discharge, Q (cu.m./sec), by regression of historical data -
• then the Peak Flood Flow = 5770 cu.m./sec
computed by the SWATCH hydrologic model
corresponds 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 (8 to 9) meters,
• these computations being consistent or matching with
the observed maximum flood water levels on 26 September 2009
relative to the low banks.
Computation of FLOOD FREQUENCY
• Compared to the
30-year Flood = 2740 cu.m./sec (design flood capacity of PMRCIP)
50- year Flood = 2980 cu.m./sec
100-year Flood = 3310 cu.m./sec
• taken from the flood frequency distribution for Marikina River at Sto Niño as
derived and adopted in the DPWH Pasig-Marikina River Channel
Improvement Project (PMRCIP) and also reviewed by NHRC in 2005,
• it is clear that the computed 2009 Peak Flood Flow = 5770 cu.m./s
has exceeded the previous 100-year flood and therefore necessitates a
review and possible revision of the flood frequency distribution.
• Nonetheless, it can be concluded that the Ketsana-Ondoy tropical storm of
100-150 year return-period has produced a record maxum flood discharge of
5770 cu.m./sec that has greatly exceeded the previously projected 100-year
flood discharge, whereas the PMRCIP design flood capacity of 30 year return
period was never exceeded before September 26, 2009.
It is expected that when more rainfall and river flow data become available for
the storm period, more refined values will be obtained without resulting
in the revision of the main conclusion already made with respect to storm and
flood frequencies or return period exceeding 100 years.
NHRC Re-evaluation of the Hydrologic Design Parameters of DPWH-PMRCIP (2005)
1. Rainfall analysis – methodology is accepted after review
- utilized the annual maximum rainfall intensities at Port Area station (1907-2000)
which has longest data in Metro Manila
- applied the Gumbel-Chow probability distribution for annual maximum rainfall
- applied the accepted rainfall intensity formulas to express intensity as
function of return period and duration of annual maximum rainfall
- derived center-concentrated type of hyetographs from rainfall intensity formulas
- obtained design storms by multiplying hyetographs with areal adjustment factors
2. Flood Run-off Analysis – methodology is accepted after review
- fitted the Log Normal probability distribution to the annual peak discharge data
at Marikina River, Sto Niño station to statistically derive design flood discharge.
- used the Storage Function Model to generate flood hydrographs from the
mountainous Upper Marikina River Basin (DA = 505.9 sq. km.) under both
existing land use (1997) and future land use (2020).
- used the Quasi-Linear Model to generate flood hydrographs from the urbanized
lower part of the Pasig-Marikina River Basin (DA = 115.1 sq.km.) under both
existing land use (1997) and future land use (2020).
- applied the areal adjustment factor to hyetographs in order for the simulated flood
peak discharge by flood runoff model to be equal to the probable discharge from
statistical analysis of annual maximum flood at Sto Niño station.
Highlights of the Hydrologic Design
Parameters of PMRCIP
1. Rainfall Data
- Historically highest 1-day rainfalls
at Port Area were as follows:
Year Max Rainfall, mm/day
(post-war with asterisks)
1970 403.1 *
1976 371.6 *
1919 310.6
1923 309.1
1924 285.0
1918 271.5
1931 265.7
1972 265.1 *
1921 263.6
1985 252.8 *
1997 241.5 *
1958 239.8 *
1961 236.2 *
1914 234.7
1977 234.4 *
2. Probable Rainfall at Port Area by
Gumbel-Chow Disribution:
Return 60-min 1-day
period Rainfall Rainfall
(years) (mm) (mm)
2 53.3 147.2
5 68.4 210.6
10 78.4 252.5
20 88.1 292.7
30 93.6 315.9
50 100.5 344.8
100 109.8 383.8
150 115.3 406.6
Comments:
The nearly 150-year rainfall was
experienced in 1970, while the
nearly 100-year rainfall was
experienced in 1976.
4. 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 Future
(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
Comments:
The 30-year flood of 2740 m3/s
has not yet been experienced in the
42-year period of record, 1958-2000.
However, the 20-year flood of 2550 m3/s
was exceeded in 1986.
3. 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.
5. Sea and Lake Boundary Conditions
Manila Bay (Pier 15)
Tide Levels
Mean Sea Level (MSL) = 10 + 0.599 m
Mean Higher High Water (MHHW) = 10 + 1.128 m
Mean Spring Higher High Water (MSHHW) = 10 + 1.391 m
Datum Level (DL) = 10 m
Laguna de Bay (north shore)
(1949-1999 data)
Historical Maxima
Year Annual Max. Water Level (m above DL)
1972 14.03
1978 13.58
1988 13.55
1986 13.34
1960 13.17
1952 13.08
etc.
Annual mean = 11.50 m.
Mean annual max = 12.34 m.
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