Professor, Institute of Civil Engineering and National Hydraulic Research Center,
College of Engineering, University of the Philippines
Diliman, Quezon City, Philippines
Special seminar at the
School of Environmental Science and Management (SESAM)
University of the Philippines - Los Baños, Laguna, Philippines
7 September 2009, 3:00p.m.
The two decades covered by 1990-2009 in the Philippines have been characterized by
extreme geophysical events with significant hydrological characteristics .
These events have been accompanied by large hazards of water excesses and deficiences
relative to the safety and requirements of the population, the economy and the environment.
Many of the events have brought about long-term impacts to the land and water resources
of the affected regions and have raised new awareness, expectations and resolve for action
for more effective water resources research and development, control and management
in the face of the uncertainties.
The physical uncertainties are found in the climatic, geophysical, and hydrological processes
which also bear the strong influence of human activities, in both the rural and urban settings,
from the upland through the lowland to the coastal areas of river basins.
The notable or remarkable events with large environmental (geological and hydrological),
engineering, agricultural and over-all economic and social significance, as well as strong
land and water policy-making and management implications. can be enumerated as follows:
The 1990 Luzon earthquake;
The 1991 Mt. Pinatubo eruption and succeeding lahars until 1996;
The 1992 flash flood and debris flow at Ormoc City;
The slope failures or landslides at Cherry Hill, Antipolo (1999),
Payatas dumpsite (2000), and Guinsaugon, Southern Leyte (2006);
The extreme El Niño episode of 1997-1998;
The second largest historical flood of Central Luzon in August 2004;
The disastrous landslides at the eastern Luzon coastal towns in December 2004;
The flooding and mudllow surrounding Mt. Mayon (2006);
… and other persistent or rising coastal hazards such as sea level rise and salinity intrusion.
Examples of time series of rainfall, streamflows, sediment transport and
water quality parameters are presented, in either observed or modeled datasets.
Selected examples of engineering mitigation measures are also given.
A map of the Philippines which shows the 20 major river basins located in 12 water resources regions. Region 3 or Central Luzon includes the Agno River Basin and the Pampanga River Basin.
Extreme Flood Events in Central Luzon (highest record: 1972 Flood)
Pantabangan Dam & Reservoir in Nueva Ecija– the multi-purpose earth dam was finished in 1974.
Pantabangan Dam Spillway in June 1976.
Map Comparison of the 30-year Normal Rainfall for month of August and the Total Rainfall measured in August 2004. Peak monsoon months in Central Luzon, Philippines: July, August, September – including rain intensification by typhoons.
Top left and right: Typhoon Aere (Marce, Phil. local name) moved along a track northeast of the Philippines and Taiwan during the period August 20-24, 2004. Bottom left: Graph of the central pressure inside Typhoon Aere versus date in August 2004.
Satellite image of Typhoon Aere on August 25, 2004. Comparison of satellite images of Central Luzon between July 31 and August 30, 2004, showing extent of flood inundation.
A map of the extent of inundation in Central Luzon on August 30, 2004 (MODIS inundation limit prepared by the Dartmouth Flood Observatory).
News photos of the Central Luzon flooding in August 2004.
Location map of the Flood Forecasting and Warning System (FFWS) network for major river basin of Luzon, Philippines. Rainfall and River Water Level Telemetry Stations in the Flood Forecasting and Warning System (FFWS).
A drainage map (left) of the Agno River Basin (drainage area = 5952 sq.km.), and adjacent Sinocalan and Bued River Basins (drainage area = 897 sq.km.) and an isohyetal map (right) of total rainfall depth measured during the peak storm period of August 24-30, 2004.
A drainage map (left) of the Pampanga River Basin (drainage area = 9759 sq.km.) and an isohyetal map (right) of total rainfall depth measured during the peak storm period of August 24-30, 2004.
Lower AGNO RIVER BASIN: A comparison between the measured August 2004 rainfall depth, and the three Pearson Type 3 distribution plots fitted to the monthly rainfall records of the synoptic station, Dagupan City, for July, August and September, respectively, in the period of record, 1961-2004. August 2004 rainfall = 1018 mm. Return period = around 10 years
PAMPANGA RIVER BASIN: A comparison between the measured August 2004 rainfall depth, and the three Pearson Type 3 distribution plots fitted to the monthly rainfall records of the synoptic station, Cabanatuan City, for July, August and September, respectively, in the period of record, 1961-2004. August 2004 rainfall = 690 mm. Return period = around 25 years
Upper AGNO RIVER BASIN: Storm hyetographs and f lood hydrographs derived from reservoir operations data of Ambuklao and Binga Dams in the upper Agno River Basin during the period, August 1 -30, 2004.
Storm hyetographs and f lood hydrographs (hourly and daily) derived from reservoir operations data of San Roque Dam in the upper Agno River Basin during the period, August 1 -30, 2004.
Lower AGNO RIVER BASIN: Storm hyetographs & stage hydrographs of lower Agno River at Bañaga (DA = 5564 sq.km.) and Sinocalan River at Sta. Barbara (DA = 180 sq.km.) during the period, August 1 – September 30, 2004.
Reservoir water balance for the Ambuklao, Binga, and San Roque Dams, Upper Agno River Basin, during the peak storm period, August 24-30, 2004 Damsite at Upper Agno River Basin Drainage area, sq.km. Peak hourly inflow discharge, m 3 /s Peak hourly outflow discharge, m 3 /s Inflow volume, MCM Outlflow volume, MCM Change in reservoir volume, MCM Ambuklao Dam 686 1273 1212 (spillway+turbine) 298.4 292.6 5.8 Binga Dam 936 1844 1891 (spillway+turbine) 468.7 469.2 - 0.50 San Roque Dam 1250 3029 SRPC: 2792, or PAGASA: 2811 (spillway) + 202 (turbine) 649.5 376.4 (spillway) + 81.8 (turbine) 191.3 (29% of inflow volume)
SAN ROQUE RESERVOIR Sediment routing modeling nhc northwest hydraulic consultants S Sediment inflow TE = Trap Efficiency Vancouver, November 20 th , 2006
Past sedimentation rates Ambuklao Binga Effect of 1990 Luzon earthquake in the period 1990-97. Effect of 1990 Luzon Earthquake in 1990-97. 5.8 64 153 1997 1.4 8 217 1986 5.3 69 225 1980 3.0 33 294 1967 - - 327 1956 Sedimentation rate (10 6 m 3 /yr) Deposited volume (10 6 m 3 ) Storage Volume (10 6 m 3 ) Year 1.0 6.1 24.0 2003 2.4 26.0 30.1 1997 1.2 8.7 56.1 1986 1.4 17.1 64.8 1979 0.8 5.5 81.9 1967 - - 87.4 1960 Sedimentation rate (10 6 m 3 /yr) Deposited volume (10 6 m 3 ) Storage Volume (10 6 m 3 ) Year
PAMPANGA RIVER BASIN: Storm hyetographs & stage hydrographs of Chico River at Zaragoza (DA = 1177 sq.km.) and Pampanga River at Arayat (DA = 6487 sq.km.) during the period, August 1 – September 30, 2004.
PAMPANGA RIVER BASIN: Storm hyetographs & stage hydrographs of Pampanga River at Candaba (DA = 7468 sq.km.) and Pampanga River at Sulipan (DA = 7489 sq.km.) during the period, August 1 – September 30, 2004.
aa j Agno River at San Roque Dam: August 2004 Peak inflow discharge = 3029 m 3 /s, return period = around 20 years, based on the Log Pearson Type 3 distribution fitted to pre-construction 1946-1980 annual flood records. Pampanga River at Arayat: August 2004 Peak discharge = 2689 m 3 /s, return period = around 6 years, based on the Extreme Value Type I distribution fitted to 1953-1979 annual flood records. Chico River at Zaragoza: August 2004 Peak discharge = 420 m 3 /s, return period = around 9 years, based on the Log Pearson Type 3 distribution fitted to 1960-1999 annual flood records. FLOOD FREQUENCY ANALYSIS
INUNDATED AREAS: Agno River Basin The MODIS inundation map shows that extensive flooding occurred in the Poponto Swamps area of the Tarlac sub-basin (in the towns of Moncada and Paniqui), near its confluence with Agno River, but far from the immediate downstream vicinity of the San Roque Dam. The flooded area can be reckoned by the difference between the DAs of the Agno River at the Urbiztondo and Bayambang stations, which is equal to 5134 - 4196 = 938 sq.km. This number is remarkably close to the reported 960 sq.km (96,000 has.) of flooded rice lands in Tarlac province. INUNDATED AREAS: Pampanga River Basin As shown by the MODIS inundation map, the extensive flooding occurred in the Candaba Swamps and the Pampanga River Delta (including the Pasac Delta downstream of the Pinatubo sub-basins). The areal extent of the Candaba Swamps is expected to be less than the difference between the DAs at the Sulipan and Arayat stations, which is equal to 7849 – 6487 = 1362 sq.km. The areal extent of the Pampanga and Pasac Delta areas is reckoned by the difference between the total DA of the Pampanga River Basin, and the combined DAs of Pampanga River at Sulipan station, and Angat River at Calumpit, which is equal to 9759 - 7849 - 1014 = 896 sq.km. (consistent with the inundation map).
Disaster Information Summary from the National Disaster Coordinating Council (NDCC): After- Effects of Southwest Monsoon Rains as of 8:00 AM, 01 September 2004 The southwest monsoon rains triggered massive flooding / flashfloods, landslides, and drowning incidents in various parts of Regions I, III, IV, CAR and NCR, the spillage of Ambuklao, Binga and San Roque Dams, the collapse of Amburayan Dike in Bangar, La Union and the breaching of Colibangbang Dike in Paniqui, Tarlac. Affected Areas: 2,113 barangays affected in 156 municipalities and 23 cities of 17 provinces in 5 Regions. Affected Population: 383,205 families or 1,858,082 persons; Casualties - 53 (43 dead, 9 injured and 1 still missing); Thirty five (35) of the 43 death toll was due to drowning, 4 electrocution, 1 cardiac arrest, and 3 covered by mudslide; the 9 injured was due to landslide, electrocution and covered by mudslides while the 1 missing was due to drowning. Damaged Houses - 69 totally and 2,464 partially; Properties Damaged - P1,315.039 M or P1.315 B (Agriculture - P1,167.551 M and Infrastructure - P147.488 M). Based on the search, rescue and evacuation operations conducted by the emergency responders: Cumulative total of families/persons displaced and evacuated to 143 evacuation centers is 9,269 families or 50,101 persons; Cumulative total of families /persons served - 114,022 families or 594,485 persons. Extent of assistance provided by NDCC, DSWD, LGUs and NGOs amounted to P17,202,693.15.
CONCLUSIONS AND MODELING RECOMMENDATION
The extensive swamps and delta areas in the Central Luzon river basins act
as flat detention basins of floodwaters which originate from the direct rainfall and
upper tributary inflows.
The exit of floodwaters towards the sea is slow due to the low hydraulic gradients
in these areas, further aggravated by urban development, roadways, fishponds,
embankments and other obstructions.
The rising water stages in the swamps and deltas can cause additional flooding by
backwater effects on the adjacent tributaries and communities.
There is a strong justification to recommend the development of a new regional
inundation model for the Central Luzon basins in order to assess and verify the
effects of extreme rainfall events, topography, modified river geometry, and
The inundation model can also simulate various design-driven flooding scenarios,
leading to quantified economic and environmental impacts for purposes of flood
mitigation planning and management.
Post Script: A more destructive storm-induced natural disaster happened in November 19-29, 2004 – the Eastern Luzon Landslides and Flooding caused by the three Typhoons Muifa, Merbok (Violeta) and Winnie. Provinces worst affected: Aurora, Quezon and eastern Nueva Ecija. Daily rainfall at Infanta, Quezon in Eastern Luzon: Nov. 19 - 45.8 mm. (Typhoon Muifa, Nov. 19-25, 2004) Nov. 20 - 192.8 mm. (antecedent 1-day peak, approx. 5-year return period) Nov. 21 - 184.5 Nov. 22 - 43.1 Nov. 23 - 22.4 Nov. 24 - 33.9 Nov. 25 - 7.3 Nov. 26 - 66.6 mm. (Typhoon Merbok (Violeta), Nov. 23-27, 2004) Nov. 27 - 1.7 Nov. 28 - 40.3 Nov. 29 - 493.5 mm. (main 1-day peak rainfall, approx. 45-year return period) (Typhoon Winnie, Nov. 29- Dec. 2, 2004) Below - News photos: Landslides and debris flows in Infanta and Real towns, Quezon. NDCC report (as of Dec. 2, 2004): 199 affected barangays In 38 municipalities, 52872 affected families Or 242,952 persons; 407 dead, 33 injured, 142 missing; Damages: Agriculture – P185.43 M Others – P 2.86 M
MODIS (Moderate Resolution Imaging Spectroradiometer) images: Northern & Central Luzon on December 04, 2004
Effects of Mt. Pinatubo sediment deposition
Multipurpose dams, and flood-control & anti-lahar dikes in Central Luzon.
Above: The church (1899 photo) as it was, until the 1991 Pinatubo eruption. Below: The church in 1996, its first floor completely buried in 1995. A church in Bacolor, Pampanga, Central Luzon, finally buried up to the second floor by the Pinatubo lahar of 1995.
Liongson, L. Q. and G. Q. Tabios III (2000). Computation with a 2-D Lahar-Flood Model in a Mt. Pinatubo Basin, Philippines . Proceedings of the Second International Conference on Debris-Flow Hazards Mitigation, Taipei, Taiwan, August 16-18. 2-d model grid of lower Pasig-Potrero River Basin, Mt. Pinatubo area. dx, dy = 250 m. 50-Year 5-Day Storm Liongson, L. Q., G. Q. Tabios III, and P. P. M. Castro (1997). 2-D Lahar-Flood Model for Pasig-Potrero River in the Mt. Pinatubo Area. First International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction, and Assessment, American Society of Civil Engineers, San Francisco, California, USA, August 7-9.
Debris-flow rheoloy: Shear Stress Balance: g (H - z) sin = a i s d 2 C l 2 sin du/dz |du/dz| Normal Stress Balance : ( s - f ) g (H-z) C cos = a i s d 2 C l 2 cos du/dz |du/dz| where H = depth of flow; z = vertical distance from the bed; du/dz = local velocity gradient; g = gravity acceleration; C = suspended solid concentration by volume; = s C + f (1-C) = mixture density; s = solid-phase density; f = fluid-phase density (water + washload); = friction slope angle; a i = Bagnold’s coefficient; d = median particle diameter; C l = linear concentration = 1 /[(C b / C) 1/3 - 1 ] = dynamic internal angle of friction;
Combined Hyperconcentrated Flow - Flood Flow Equations Shear Stress Balance: g (H - z) sin = (a i s d 2 C l 2 sin + K T 2 z 2 ) du/dz |du/dz| Normal Stress Balance : ( s - f ) g (H-z) C cos = (a i s d 2 C l 2 cos + K N 2 z 2 ) du/dz |du/dz| K T = von Karman coefficient for shear turbulent stress K N = similar coefficient for normal turbulent stress Total Continuity Equation: H/ t + (HU)/ x + (HV)/ y + E / C b = q - I Total Momentum Equations (x and y components): ( HU)/ t + ( HU 2 )/ x + ( HUV)/ y + gH ( H/ x + Z b / x + S fx ) + b E U/ C b = (H T xx )/ x + (H T xy )/ y + L q U L ( HV)/ t + ( HVU)/ x + ( HV 2 )/ y + gH ( H/ y + Z b / y + S fy ) + b E V/ C b = (H T yx )/ x + (H T yy )/ y + L q V L Sediment Continuity Equation: (HC)/ t + (HUC)/ x + (HVC)/ y + Z b / t C b = q C L
where t = time; (x,y) = perpendicular horizontal coordinates; H = H(x,y,t) = depth of flow; Z b = Z b (x,y,t) = bed elevation; (U,V) = (U(x,y,t), V(x,y,t)) = mean velocity vector (depth-averaged); C = C(x,y,t) = suspended solid concentration by volume; C b = bed-deposited concentration by volume; = s C + f (1-C) = mixture density; g = gravity acceleration; s = solid-phase density; f = fluid-phase density (water + washload); E = Z b / t C b = bed deposition (>0) or erosion (<0) rate; (S fx , S fy ) = (U,V) S f / (U 2 +V 2 ) = vector of friction slope components; S f = resultant bed friction slope = f (U 2 +V 2 ) /(8 g H); f = integrated friction factor (defined under rheology); T xx = n f / 8 H 2 U/ x U/ x = lateral normal stress in x-direction; T yy = n f / 8 H 2 V/ y V/ y = lateral normal stress in y-direction; T xy = T yx = t f / 8 H 2 ( V/ x + U/ y) V/ x + U/ y = lateral shear stress in either x or y direction; n , t = lateral normal and shear stress coefficients, resp. 1.0; q = total lateral inflow (such as direct rainfall or tributary flow); q C L = lateral sediment inflow; I =bed infiltration rate = a maximum assumed value or else the available water depth per unit time step, whichever is less at any given time; b E (U,V)/ C b = momentum loss vector due to deposition (for E>0 only), including entrained water; L q (U L ,V L ) = lateral momentum influx vector.
Based on a SIR-C/X-SAR Space Shuttle false-color Image of the Pinatubo-affected Pasac Delta, or Guagua RB, adjacent to the Pampanga River Basin (1994). Much of Pasac Delta has been converted to fishponds through the centuries, and at present, its narrow channels receive the fine lahar sediment brought down from the pyroclastic deposits of the 1991 eruption of the volcano .
Coastal flooding due to groundwater extraction (Siringan et al, UP NIGS, 2000.)
The demolition of illegally built additional fishponds in the estuary of the Pinatubo-affected Pasac Delta, adjacent to the Pampanga River Basin. Coastal flooding due to channel constrictions.
Opposition to major flood-control projects Major flood-control and river engineering projects have encountered opposition from local populations in the floodplain or riverbank areas due to the conflicting land-use management policies and priorities. These oppositions have caused the national government to either revise or realign, defer or abandon the project control plans. An example below:
The hydrologic cycle. (source: www.lexingtonwaterfacts.com)
Water Resources Management = (natural + engineering + social) sciences
Water for Life
(domestic water supply & sanitation)
* Highest priority under the
Water Code of the Philippines
Water for Food
(irrigation, fisheries &
Water for the Economy
(industrial & commercial water
supply, hydropower , navigation,
tourism, recreation, etc.)
Water for the Environment
(upland catchment, floodplain,
& coastal management; and
wastewater management for
sustainability, biodiversity, and
preservation of scenic, cultural
and historical places.
* Legal minimum is 10% of the
80% dependable flow at
a river diversion site.
Competition and conflict among & between: Consumptive and non-consumptive users; In-stream and onsite users.
DENR Water Quality Criteria / Water Usage & Classification for Fresh Water Class A - Public water supply II (require complete treatment to meet national standards for drinking water) Class B - Recreational water class I (for contact recreation as bathing and swimming) Class C - Fishery water for the propagation and growth of fish (also non-contact recreation & industrial use class I) Class D - For agriculture, irrigation, livestock watering and industrial water supply class II
Integrated Water Resources Management or IWRM , having been promoted in the last twelve years (1997-2009), is an international movement which advocates the multi-stakeholder and participatory manner of managing the water resources among the competing users. The Global Water Partnership (GWP) "was founded in 1996 by the World Bank, the United Nations Development Programme (UNDP), and the Swedish International Development Agency (SIDA) to foster integrated water resource management (IWRM), and to ensure the coordinated development and management of water, land, and related resources by maximizing economic and social welfare without compromising the sustainability of vital environmental systems." (http://www.gwpforum.org). Philippine Water Partnership (PWP) - established in 2002; the local network partner of GWP and GWPSEA; recognized (by NEDA InfraCom) as the principal NGO for the promotion of IWRM.
Towards a new paradigm - from sub-sectoral to cross-sectoral water management IWRM is the ‘integrating handle’ leading us from sub-sectoral to cross-sectoral water management. CROSS-SECTORAL DIALOGUE THROUGH IWRM IWRM People Food Industry & others WATER USE SECTORS Eco- system IWRM is a process which promotes the coordinated development and management of water, land and related resources in order to maximize the resultant economic and social welfare in an equitable manner without compromising the sustainability of vital ecosystems (GWP/TAC).
How do the Dublin principles translate into action? The ENABLING ENVIRONMENT sets the rules, the INSTITUTIONAL ROLES and functions define the players who make use of the MANAGEMENT INSTRUMENTS . ECOSYSTEM SUSTAINABILITY Enabling Environment Policies Legislation Management Institutional Instruments Roles Assessment Central-local Information Public-private Allocation tools River basin ECONOMIC EFFICIENCY SOCIAL EQUITY All this depends on the existence of popular awareness and political will to act!
Left: Angat Reservoir monthly inflows, releases for irrigation and water supply, and water surface elevation, relative to the lower rule curve; right: policy summary for the years 1997-2003: in scatter plots and regression curves [ Liongson (2003)] . WATER SUPPLY versus IRRIGATION : 1997-1998 El Ni ñ o period (NWRB data).
http://llda.gov.ph/SD_Mondriaan/WM_Main.htm The Water Mondriaan is a schematic map of the Laguna de Bay water system, showing the monitoring results in the lake and its tributaries compared with the DENR water quality criteria / water usage & classification for freshwater systems or when absent the LLDA expert opinion. The parameters included, focus on factors of significant ecological, human health and resource use importance or on the processes that are crucial to them: oxygen and oxygen demand (%DO, BOD5 and COD), bacterial pollution (Total Coliforms, Fecal Coliforms, eutrophic level (phosphate, dissolved nitrogen, chlorophyll-a and phytoplankton abundance), and hazardous substances (oil & grease and on a quarterly basis lead, hexavalent chromium & cadmium).
Fish pens (top) & Fish cages (bottom) used for aquaculture in Laguna de Bay. Small fisherman engaged in open lake fishing. Impact of El Niño on aquaculture and fisheries [ Liongson (2003)]
Rainfall (in drought conditions), lake stage (severe drawdown), & salinity (maximized conditions) during the El Niño months of 1997-1998. Impact of El Niño on aquaculture and fisheries This situation was most advantageous for the brackish-water aquaculture and fisheries , but disadvantageous for potential water-supply and irrigation uses. [ Liongson (2003)]
Monthly measurements of salinity, transparency and turbidity at Laguna de Bay West-Bay-I station during the years 1997-1999. (a). Time series plots and (b). Scatter plots and fitted regression lines of salinity versus transparency and turbidity. Impact of El Niño on aquaculture and fisheries [ Liongson (2003)]
The Study of the Effects of Payatas Dumpsite to the La Mesa Reservoir (NHRC, UP Diliman, 2001) The principal objective of the study is to identify the effects of the Payatas open dumpsite on the Novaliches (La Mesa) Reservoir with emphasis on the potential risk of leachate contamination. The secondary objectives are: to characterize the hydrogeology and hydraulics of the aquifer below the Payatas dumpsite, to identify the toxic and hazardous contaminants which have leached to the subsurface beneath the Payatas dumpsite area, to establish the potential risk of contamination to the La Mesa Reservoir, and to recommend possible remedial or mitigating measures to reduce the risk of contamination of the La Mesa Reservoir.
Hydraulic Model test for the
Laoag River Basin Flood Control
and Sabo Project (2002)
The main objective of this study of UPERDFI-NHRC
is to conduct hydraulic model test in order to confirm
the flow conditions of the alluvial fan rivers and effects
on spur dike system in the Cura/Liabugaon, Solsona,
Madongan and Papa Rivers in the Laoag River Basin in
Ilocos Norte. This physical movable-bed modeling study
provides technical inputs to the JICA-assisted DPWH
lood control and sabo project for the
Laoag River Basin.
Sabo Dam at Ormoc, Leyte.
Hydraulics – engineering mechanics of water flows. Systems of flow equations - Navier-Stokes Equations, (general incompressible Newtonian fuid); St. Venant’s Equations and Kinematic Wave Equation. (open channel flows).
A simple physically-based model - admits effects of urbanization & climate change on flash floods.