Available via license: CC BY 4.0
Content may be subject to copyright.
Proc. IAHS, 386, 95–100, 2024
https://doi.org/10.5194/piahs-386-95-2024
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.
Open Access
ICFM9 – River Basin Disaster Resilience and Sustainability by All
Hydrodynamic Investigation of Laguna Lake, Philippines
for Water Security and Flood Risk Management
of Metro Manila
Eugene C. Herrera1and Kensuke Naito2
1Institute of Civil Engineering, University of the Philippines, Diliman Quezon City, 1101, Philippines
2International Center for Water Hazard and Risk Management – ICHARM, Public Works Research Institute
(PWRI), Tsukuba, Ibaraki, Japan
Correspondence: Eugene C. Herrera (echerrera1@up.edu.ph)
Received: 20 July 2023 – Revised: 7 November 2023 – Accepted: 24 November 2023 – Published: 19 April 2024
Abstract. Laguna Lake, strategically located at the center of urban development, Metro Manila, is the focal
point of national development efforts for economic activities, including flood disaster operation. It is the most
stressed inland water body at the same time however, with competing and conflicting water-users, and continued
environmental degradation from anthropogenic-based stressors. The use of the lake as a source of raw water
for domestic supply have become more significant and critical over the past recent years with the aggravating
condition of water scarcity in Metro Manila. It also serves as an important flood-detention storage for Metro
Manila during the rainy season, with flow diversions from upstream Marikina river basin. This study presents
a three-dimensional hydrodynamic study of Laguna Lake to understand the physical processes that govern and
influence lake hydraulics for various water uses. A hydrodynamic model was set-up incorporating spatial and
temporal variations in wind forcing and watershed river discharges, and dynamic sea interaction. Simulation
results reveal a significant increase in lake salinity concentration for incremental increases in lake water abstrac-
tion, particularly during the dry season. A numerical experiment on bathymetric evolution also showed various
Pasig River hydraulic discharge features and an increase in hydraulic residence time of the lake. Modelling anal-
ysis on the lake’s flood detention function on the other hand revealed different shore-land flood inundation areas
and recession durations for varying lake-flood detention levels that warrants the need for a more comprehensive
and sustainable flood management operation in the metropolis. Results from this study substantiate scientific
information for outlining management approaches and conservation strategies especially for fast developing en-
vironments.
1 Introduction
Laguna Lake with substantial economic value for water re-
source development is the most important natural resource
in the Philippines. Situated adjacent to a thriving mega city,
Metro Manila, it is the focal point of national development
efforts not only in the agriculture and fishery, water supply
and energy sectors, but in the regional development program
as well (Santos-Borja and Nepomuceno, 2003). However, it
is the most stressed inland water body at the same time with
competing and conflicting water-users, and continued envi-
ronmental degradation from anthropogenic-based stressors.
The lakes’ dynamic interaction with Manila Bay through
Pasig River makes it ideal for fishery and aquaculture with
the entry of salt-water, but at the same time discharges
nutrient-rich polluted waters of Metro Manila and surround-
ing coastal provinces to the lake (Tabios III, 2020). The lake
has also been traditionally utilized as a water resource for ir-
rigation, power-plant cooling, hydropower generation, recre-
ation, and transport route for people and products. It also
serves as flood-detention storage for Metro Manila during the
rainy season. More recently, it has been tapped as a source of
raw water for domestic supply. Discussions on maximizing
the use of the lake for this function have become more sig-
Published by Copernicus Publications on behalf of the International Association of Hydrological Sciences.
96 E. C. Herrera and K. Naito: Hydrodynamic Investigation of Laguna Lake
nificant and critical over the past recent years with the aggra-
vating condition of water scarcity in Metro Manila and the
vicinity. With the lake’s invaluable water resource, competi-
tion and conflicts among its stakeholders are common occur-
rences. Approximately twenty million inhabitants depend on
the lake for environmental goods and services.
Flooding occurs when lakes, riverbeds, soil and vegeta-
tion cannot absorb all the water. In the case of Laguna Lake,
it serves as a detention storage of floodwaters that drains
the Pasig-Marikina-Laguna Lake basins during intense rain-
fall events. Mangahan Floodway is opened for flood diver-
sion to Laguna Lake through the Rosario Weir when Sto.
Nino (station along Marikina River) water elevation reaches
4.5 m a.s.l. (Fig. 1). By design, the Mangahan Floodway is
capable of handling 2400 m3s−1of water flow. To comple-
ment the floodway, the Napindan Hydraulic Control Struc-
ture (NHCS) was built in 1983 at the confluence of the
Marikina River and the Napindan channel of the Pasig River
to regulate the storage of flood waters in the lake during
extreme rainfall events, and at the same time the tidal flow
of saline water from Manila Bay to prevent the intrusion of
polluted water into the lake during the dry season. It has a
fully gated diversion dam at its head and was designed with
a width of 260 m. Over 40 000 households are situated along
the floodway’s banks and these shoreline slums have reduced
its effective width to 220m. The flood-control system’s op-
erational rule, that is based on flood depths and channel dis-
charge capacities, has not been updated since its first oper-
ation in 1986. With the competing and conflicting use of
the lake waters, management of this flood-detention func-
tion has not been carried-out effectively. NHCS which was
to close its gates after diverting floodwaters from Marikina
River (through Mangahan Floodway) to detain water tem-
porarily in the lake as part of flood operation were almost
never closed to allow saline water to enter the lake since it
benefits the aquaculture industry and fisheries sector. Thus,
the NHCS was practically never operated for purposes of
tidal flow regulation or pollution control.
By carrying flood waters to Laguna Lake, the Mangahan
Floodway lessens flood conditions in Metro Manila but con-
tributes to flooding of the coastal areas of Taguig, Taytay, and
other towns in Laguna and Rizal along the lake. Incidents
of severe floods became more frequent and lasted longer in
these areas since its construction. An unusual large flood oc-
curred in October/November 1986, lasting for 2 months and
resulting in high mortality and morbidity rates due to gas-
troenteritis and other water-borne diseases (Jorgensen and
Vollenweider, 1988).
Furthermore, pollution and sediments carried by the flood-
way has jeopardized the existing and potential uses of the
lake. The sedimentation rate of the lake is estimated at
1.5 million m3yr−1with the Marikina River as a major con-
tributor of silt to the lake through the Mangahan Floodway
(Santos-Borja and Nepomuceno, 2003). Additional pollution
and siltation come from the shoreline settlers, living in slums
up to 5 rows deep, whose waste goes directly into the flood-
way (JICA, 2018).
The pressures of both growing user-demand and declining
water quality laid ground the value of scientific knowledge
on lake environmental-functioning for the optimal and sus-
tainable use of the lake water resources. This study investi-
gates the hydrodynamic features of Laguna Lake with the use
of high-resolution numerical modelling analyses. The study
aims to clarify the circulation and transport features of the
lake and provide information on the hydraulics of the lake
for different lake-water use and assess critical lake ecosys-
tem conditions.
2 Methodology
This paper presents a three-dimensional hydrodynamic study
of Laguna Lake to properly understand the physical pro-
cesses that govern and influence the circulation and mass
transport characteristics of the lake for various water uses.
The model was set-up to take into account the physical ef-
fects of natural climatic and hydrologic factors such as dis-
charges from rivers, direct lake rainfall and evaporation, lake
groundwater interaction, wind induced circulation, and tidal
fluctuation at Manila Bay. Fish pen and fish cage structures
used for aquaculture, affecting lake circulation were also in-
corporated into the model, in addition to different lake wa-
ter withdrawals. The hydrodynamic component of Delft3D,
FLOW was utilized to simulate the physics of the lake.
Delft3D-FLOW solves the Navier Stokes equations for an in-
compressible fluid, under the shallow water and the Boussi-
nesq assumptions. In the vertical momentum equation, the
vertical accelerations are neglected, which leads to the hydro-
static pressure equation. In 3D models, the vertical velocities
are computed from the continuity equation. The set of par-
tial differential equations in combination with an appropriate
set of initial and boundary conditions is solved on a finite
difference grid. Reference is made to the technical reference
manual (Delft Hydraulics, 2007) for these formulations. The
unsteady shallow-water equations were solved in 3D with a
vertical sigma-coordinate system laid-out on a horizontal or-
thogonal curvilinear grid. Flow is forced by tide at the open
boundary, wind stress at the free surface, and pressure gradi-
ents due to free surface (barotropic) and density (baroclinic)
gradients. Sediment transport and morphologic changes were
not included in the simulations. The hydrodynamic model
was calibrated and validated using hydrographic data from
field surveys and long-term monitoring information (Herrera
et al., 2015; Japan International Cooperation Agency, 2018).
3 Results and discussion
3.1 Flood detention operation
Laguna Lake serves as a flood-detention storage for Metro
Manila (Fig. 1). Excess runoff discharge from Marikina
Proc. IAHS, 386, 95–100, 2024 https://doi.org/10.5194/piahs-386-95-2024
E. C. Herrera and K. Naito: Hydrodynamic Investigation of Laguna Lake 97
Figure 1. Metro Manila flood mitigation infrastructures and sur-
rounding watersheds and water bodies.
Basin is diverted to the lake for temporary storage until flood
waters from the watershed recedes. In 26 September 2009,
typhoon Ketsana (local name Ondoy) dumped about 45 cm
of rain in 12 h that resulted to widespread flooding. A 1.2 m
increase in lake level that occurred due to the flood deten-
tion operation took months to recede causing flood waters in
shoreland areas to last until January of the following year
(Figs. 2 and 3). Although, the volume of water generated
by Ketsana would have resulted to flooding nonetheless even
with a fully operational flood management and control sys-
tem, there are measures that can be taken to reduce the im-
pact of such extreme event to a predetermined safety level.
Among these include effective regulation of both Mangahan
Floodway and NHCS operation using updated hydraulic in-
formation, enhancement of the monitoring and early warn-
ing system within the Pasig-Marikina-Laguna Lake basin, in-
creasing the flow capacity of Napindan channel, and others.
Scenario simulations revealed different shore-land flood in-
undation areas and recession durations for varying lake flood
detention levels (Fig. 3 and Table 1). Pasig takes the longest
time to recede back to normal water levels (10.5m based
on Laguna Lake Development Authority datum) at roughly
219 d. It is followed by Cainta at 194–204 d, then Napindan
at 169 d, Taytay at 141 d, Pateros at 119d and Taguig at 40–
84 d. Other flooding hydraulic details from the hydrodynamic
modelling conducted are presented in Table 1.
Although the operation of these existing flood control in-
frastructure (Rosario Weir, Mangahan Floodway, and NHCS)
during typhoon Ketsana lessened the flood conditions in
Metro Manila, it significantly contributed to flooding of the
coastal areas around Laguna Lake. Based on the results of
the numerical simulation (Fig. 3 and Table 1), there is an ap-
Figure 2. Laguna Lake water level simulation and validation of the
Typhoon Ketsana event.
Figure 3. Laguna Lake shoreland flooding at different inundation
levels.
parent need to effectively manage the operation of the lake
for flood detention so as not to cause flooding to shoreland
communities. The results also call for immediate action on
updating the operational rule of the flood control system and
improving the discharge capacities of the critical channels in
the system, particularly the Mangahan Floodway, Napindan
channel, Pasig River and lower Marikina River.
3.2 Bathymetric change and eutrophic vulnerability
The watershed of the lake has undergone significant changes
from population growth, urbanization, industrialization, and
land use conversion, resulting to increased siltation, eutroph-
ication and pollution (Nauta et al., 2003). Rivers emptying
to the lake unload wastes, organic matter, and sediments
that settle and accumulate on the lakebed. A hydrodynamic
model experiment for different lake bathymetric configu-
ration (1963, 1983 and 2008) showed various Pasig River
https://doi.org/10.5194/piahs-386-95-2024 Proc. IAHS, 386, 95–100, 2024
98 E. C. Herrera and K. Naito: Hydrodynamic Investigation of Laguna Lake
Table 1. Hydrodynamic matrix of Laguna Lake during flood detention operation.
Water Lake Lake Change Change Pasig Time to Flooded
Level Area Volume in in Flood River Recede Municipalities
(m a.s.l.) (×106(×106Elevation Area (×106Outflow to
m2) m3) (m) m2) (×106normal
m3d−1) (d)
3.5 1101.7 5573.1 – – 32.3 219 Pasig
3.3 1087.7 5354.4 0.2 14.0 31.5 204 Cainta
3.0 1067.6 5031.0 0.3 20.1 29.4 194 Cainta
2.5 1033.6 4506.3 0.5 34.0 25.3 169 Napindan
2.0 998.0 3998.0 0.5 35.6 22.5 141 Taytay
1.5 960.9 3508.0 0.5 37.0 19.5 119 Pateros
1.0 923.3 3037.1 0.5 37.6 11.9 84 Taguig
0.5 891.3 2582.9 0.5 31.9 5.6 40 Taguig
0.0 849.1 2146.8 0.5 42.2 2.1 – –
hydraulic discharge features and an increase in hydraulic
residence time of the lake in terms of salinity distribution
(Fig. 4). The historical change in lake bathymetry from years
of deposition, erosion and reworking of sediments brought
forth the changes in circulation pattern that led to the longer
residence time of the lake. Erosion and deepening in the
northern west and east lobes of the lake in particular could
have retarded lake outflow-directed circulation. More pol-
luted seawater was also observed to be intruded during the
dry season due to the longer lake residence time. Seawater
entry demonstrated larger extent in intrusion plume as a re-
sult which further established the increase in eutrophic vul-
nerability and higher potential for adverse response to eu-
trophication of Laguna Lake in recent years. Thus, it is re-
vealed from the numerical experiment that eutrophic vulner-
ability in Laguna de Bay is not a simple function of anthro-
pogenic waste loading but watershed sediment input as well
with the accompanying changes in circulation patterns. Re-
sults from this numerical scenario analysis warrants the need
for a better management of the sediment and pollution load-
ing of rivers to the lake.
3.3 Increasing lake abstractions and lake
hydrodynamics
Scenario simulations were also conducted to study the im-
pact of increased lake water abstractions on the lake hydro-
dynamics, particularly the entry of polluted salt water from
Manila Bay through the Pasig River. Simulation results re-
veal a significant increase in lake salinity concentration for
incremental increases in lake water abstraction, particularly
during the dry season. Different abstraction scenarios cor-
responded to different current movement patterns and con-
centration distributions of the lake saltwater plume (Figs. 5
and 6). With the drop in lake water level by about 1.5–2.0 cm
for every 400 million L d−1lake water abstraction during
the dry season, Pasig River backflow (Manila Bay to Laguna
Lake) is induced by the intensified hydrodynamic imbalance
between the lake and the bay resulting to higher incidence
of lake salinity intrusion. With the drop in annual average
Pasig River outflow (Laguna Lake to Manila Bay), the even-
tual exit of saline water from the lake (the lake hydraulic
residence time), will take a longer period compared to the
hydrodynamic condition without abstraction, increasing La-
guna Lake’s eutrophic vulnerability. In spite of the sheer vol-
ume of the lake waters, and its high potential for raw water
abstraction and use, a scientific-based permitting guideline
needs to be in place to sustainably manage requests for water
abstraction and prevent any deleterious effects on the lake’s
environmental functioning.
4 Conclusions
A 3-dimensional hydrodynamic model was set-up for La-
guna Lake, Philippines using Delft-3D to properly under-
stand the physical and environmental processes that govern
and influence the lake dynamics. The water balance of the
lake was analyzed by taking into account the physical ef-
fects of all natural climatic and hydrologic factors, as well
as man-made interventions. Field measurement data on var-
ious water quality and hydrodynamic parameters were used
for the calibration and validation of the model. Observed lake
parameters were reproduced by the model within acceptable
limits of accuracy.
In general, in spite of the data limitations, the hydrody-
namic set-up and simulation results showed that the hydro-
dynamic model can describe the water balance and trans-
port processes in Laguna Lake within sound degree of accu-
racy. The validated model was able to provide useful infor-
mation for understanding the dynamic condition of the lake
and for predicting the impacts of future man-made interven-
tions, such as temporary flood detention and water abstrac-
tion for domestic use. Baseline information has been gener-
ated to form the scientific foundation of probable protective
Proc. IAHS, 386, 95–100, 2024 https://doi.org/10.5194/piahs-386-95-2024
E. C. Herrera and K. Naito: Hydrodynamic Investigation of Laguna Lake 99
Figure 4. Hydrodynamic simulation for seawater intrusion plume
of the 2008, 1983 and 1963 lake bathymetric scenarios.
regulations and policies for Laguna Lake. Considering La-
guna Lake is a multi-purpose reservoir, water allocation and
flood-detention function require greater analysis and under-
standing of the dynamics of its environment for it to be man-
aged sustainably. Thus, deeper and better understanding of
the lake dynamics generated can serve as a sound basis for
lake management options and for further research undertak-
ings, essential for the lake’s optimal and sustainable use as
a multi-purpose resource, while preserving its environmental
integrity at the same time.
Figure 5. Laguna Lake circulation patterns for various abstraction
rates.
Figure 6. Laguna Lake dry season salinity plume in parts salinity
units for various abstraction rates.
Data availability. Only processed data directly used for the final
version of the model are available upon request. Raw data are to be
gathered from the agencies from which the authors collected such
datasets.
Author contributions. ECH conceptualized, set up and simulated
the models, conducted the extraction, analysis, and documentation
of model results. KN reviewed the abstract and supported the overall
study for its submission to the ICFM9 conference.
https://doi.org/10.5194/piahs-386-95-2024 Proc. IAHS, 386, 95–100, 2024
100 E. C. Herrera and K. Naito: Hydrodynamic Investigation of Laguna Lake
Competing interests. At least one of the (co-)authors is a guest
member of the editorial board of Proceedings of IAHS for the spe-
cial issue ”ICFM9 – River Basin Disaster Resilience and Sustain-
ability by All”. The peer-review process was guided by an indepen-
dent editor, and the authors also have no other competing interests
to declare.
Disclaimer. Publisher’s note: Copernicus Publications remains
neutral with regard to jurisdictional claims made in the text, pub-
lished maps, institutional affiliations, or any other geographical rep-
resentation in this paper. While Copernicus Publications makes ev-
ery effort to include appropriate place names, the final responsibility
lies with the authors.
Special issue statement. This article is part of the special issue
”ICFM9 – River Basin Disaster Resilience and Sustainability by
All”. It is a result of The 9th International Conference on Flood
Management, Tsukuba, Japan, 18–22 February 2023.
Acknowledgements. The authors would like to express gratitude
to Laguna Lake Development Authority, to their former Integrated
Water Resources Management Division for all the assistance and
logistical support during the field surveys, as well as the mainte-
nance of the IMSWES monitoring platform. Appreciation is also
given to the Department of Science and Technology (DOST) for
facilitating the entry of instruments. This research was supported
by The Japan Society for the Promotion of Science (JSPS) Grant-
in-Aid for Scientific Research [No. 18254003, No. 20121007 and
No. 21254002]; JSPS Core University Exchange Program; Asia-
Pacific Network (APN) Grant [ARCP2006-08NMYNadaoka]; Sci-
ence and Technology Research Partnership for Sustainable De-
velopment (SATREPS) in collaboration between Japan Science
and Technology Agency (JST, JPMJSA1909) and Japan Interna-
tional Cooperation Agency (JICA); and the Department of Science
and Technology (DOST) and DOST Philippine Council for Indus-
try, Energy and Emerging Technology Research and Development
(DOST-PCIEERD) through the project Eco-System Modelling and
Material Transport Analysis for the Rehabilitation of Manila Bay
(e-SMART) under the IM4ManilaBay Program.
Financial support. This research has been supported by the Sci-
ence and Technology Research Partnership for Sustainable Devel-
opment (grant no. JPMJSA1909) and the Department of Science
and Technology, Philippines (grant no. Eco-System Modelling and
Material Transport Analysis for the Rehabilitation of Manila Bay
(e-SMART) Project).
Review statement. This paper was edited by Shinji Egashira and
reviewed by two anonymous referees.
References
Delft Hydraulics: Simulation of multi-dimensional hydrodynamic
flows and transport phenomena, Delft3D-FLOW User Manual
Version 3.14, WL/ Delft Hydraulics, the Netherlands, 642 pp.,
https://content.oss.deltares.nl/delft3d4/Delft3D-FLOW_User_
Manual.pdf (last access: 4 March 2024), 2007.
Herrera, E. C., Nadaoka, K., Blanco, A. C., and Hernandez, E. C.:
Hydrodynamic Investigation of a Shallow Tropical Lake Envi-
ronment (Laguna Lake, Philippines) and Associated Implications
for Eutrophic Vulnerability, ASEAN Engineering Journal, 4-1,
48–62, https://doi.org/10.11113/aej.v4.15432, 2015.
Japan International Cooperation Agency: Resettlement Action Plan
for Mangahan Floodway, Pasig-Marikina River Channel Im-
provement Project Phase IV Report, 1-1–1-3, September 2018.
Jorgensen, S. E. and Vollenweider, R. A. (Eds.): Principles of Lake
Management, in: Guidelines of Lake Management, International
Lake Environment Committee Foundation, United Nations Envi-
ronment Programme, 191 pp., ISBN: 4-906356-27-3, 1988.
Nauta T. A., Bongco, A. E., and Santos-Borja, A. C.: Set-up of a
decision support system to support sustainable development of
the Laguna de Bay, Philippines, Mar. Pollut. Bull., 47, 211–218,
https://doi.org/10.1016/S0025-326X(02)00407-1, 2003.
Santos-Borja, A. and Nepomuceno, D.: Experience and Lessons
Learned Brief for Laguna de Bay, Philippines, Presented in
the Lake Basin Management Initiative ILEC/LakeNet Regional
Workshop for Asia: Sharing Experience and Lessons Learned in
Lake Basin Management, Manila, Philippines, 1–4 September
2003, 225–258, https://iwlearn.net/documents/6001 (last access:
4 March 2024), 2003.
Tabios III, G. Q.: Water Resources Systems of the Philip-
pines: Modeling Studies, 4, 403 pp., ISBN 978-3-030-25400-
1, Springer Nature, Switzerland, https://doi.org/10.1007/978-3-
030-25401-8, 2020.
Proc. IAHS, 386, 95–100, 2024 https://doi.org/10.5194/piahs-386-95-2024
