Floods: Mitigation and Adaptation

Opening Session

The forum opened with a presentation of the house rules, setting the tone for a respectful and productive discussion. This was followed by an opening prayer led by Medardo Pizarra, President of Norwich Brent Cedric School, Inc., and a rendition of the Philippine National Anthem.

The moderators, Marie Marciano of SALIKA and David D’Angelo, representing Boses ng Kalikasan, Green Party of the Philippines, Bayanihan para sa Kalikasan, and Green Convergence, introduced themselves and provided an overview of the Kamayan para sa Kalikasan Forum.

Victoria Segovia, President of Green Convergence, delivered the opening remarks. She highlighted the devastating impact of recent typhoons, which had affected Visayas, Luzon, and Mindanao. Segovia detailed the cascading effects of these events, including landslides, fatalities, loss of property, displacement, crop destruction, canceled classes and work, and large-scale evacuations. Her address emphasized the urgency of adopting effective flood mitigation and adaptation strategies.

Marciano outlined the flow of the webinar, explaining that it would begin with expert presentations, followed by an open forum for participants to share questions and insights.

Session One: Addressing Floods in the Philippines

Resource Person:
Dr. Guillermo Tabios III
Professor Emeritus
Institute of Civil Engineering
University of the Philippines Diliman

The Philippine Context

Dr. Guillermo Tabios provided a comprehensive overview of the Philippines’ susceptibility to flooding. As a tropical, archipelagic nation, the country is characterized by interconnected rivers, lakes, and aquifers that merge with deltas, estuaries, and coasts. Its location near the equator results in a warm, humid climate with heavy rainfall caused by typhoons, monsoons, inter-tropical convergence zones (ITCZ), and thunderstorms. This climate, combined with steep mountain streams prone to soil erosion, contributes to flooding and sedimentation issues.

Dr. Tabios used historical data to illustrate the gravity of these challenges. He discussed the catastrophic rainfall brought by Typhoon Ondoy (September 26, 2009), noting that maximum 6-hour rainfall reached 381.5 mm and 12-hour rainfall peaked at 448.5 mm—figures associated with 180-year return period storms. He also examined the recent Typhoon Carina (July 19-26, 2024) and its accompanying habagat (southwest monsoon), which resulted in rainfall of 400-500 mm over 24 hours for seven consecutive days.

Vulnerability to Erosion and Coastal Deposition

Dr. Tabios presented findings from a study by Browning and Sawyer (2021) that identified Central Luzon and Metro Manila as high-risk areas for soil erosion. He outlined risk factors such as land cover type, annual precipitation, soil thickness, bedrock lithology, watershed slope, and human activities like agriculture, mining, and urban development. Coastal areas were similarly vulnerable due to erosion and deposition, with risks measured on a scale from Very Low (1) to Very High (5).

Urban Flooding: The Case of the Pasig-Marikina River Basin

The discussion shifted to urban flooding challenges in the Pasig-Marikina River Basin, highlighting the interplay of environmental degradation and human activity:

• Forest Denudation and Quarrying: Increased erosion and sediment load in rivers.
• Local Drainage Issues: Floodwaters trapped without an outlet to rivers or floodways.
• Garbage Disposal Problems: Clogged waterways and water pollution.
• Manggahan Floodway: Originally designed with a 280-meter width and a high-water level capacity of 14 meters, the floodway’s efficiency has diminished due to narrowing and sedimentation.
• Improper Land Use and Zoning: Unauthorized settlements and subdivisions within flood-prone areas like Laguna Lake exacerbate risks.

Dr. Tabios emphasized the urgent need for sustainable land-use planning and improved infrastructure to address these vulnerabilities.

Holistic Flood Risk Management in the Context of Integrated Water and Coastal Management (IWRCM)

Flood risk management is intrinsically linked to broader aspects of land use management, affecting water resources, coastal zones, and hazard mitigation efforts. A holistic approach is essential to address the complexities of these interdependencies.

Key Concepts in Integrated Flood Management

Source-to-Sea (S2S) Continuum
The S2S continuum emphasizes the interconnectedness of water systems from their source (rivers and watersheds) to their ultimate endpoint (oceans). This perspective ensures that water and resource management strategies consider upstream and downstream impacts to promote ecological and social sustainability.

Cloud-to-Coast (C2C) Approach

The C2C approach highlights the need for an integrated understanding of water systems, encompassing atmospheric processes (clouds), terrestrial hydrology (rivers and groundwater), and coastal dynamics. It aims to create a seamless framework for managing water resources and mitigating flood risks across all stages of the hydrological cycle.

Integrated Water Resources Management (IWRM) and Integrated Coastal Management (ICM)

IWRM seeks to balance water use and conservation across sectors and stakeholders, while ICM focuses on the sustainable management of coastal areas. Together, they form a unified framework for addressing water and flood-related challenges holistically.

Hydrologic, Geomorphologic, and Ecologic Interactions

Capturing the interplay of hydrology, geomorphology, and ecology is vital for effective flood management. These interactions influence sediment transport, water flow, and ecosystem health, which collectively shape flood behavior and impacts.

Flood Management: Sustainability Science vs. Traditional Science

Dr. Guillermo Tabios outlined the evolution of flood management, contrasting traditional science (TS) with sustainability science (SS).

1. Aims of Study

• TS: Focuses on understanding individual components to manage them separately.
• SS: Seeks to understand interrelations between components to manage systems holistically.

1. Modes of Change

• TS: Assumes static systems and designs based on historical stationarity.
• SS: Recognizes dynamic, non-stationary systems shaped by climate, land use, and socio-economic shifts.

1. Truth Verification

• TS: Relies on controlled experiments and historical data.
• SS: Emphasizes real-world evolution and integrated management.

1. Research Outcomes

• TS: Generates knowledge for analysis and localized solutions.
• SS: Creates actionable insights for adaptive, integrated management across scales.

1. Expected Outcomes

• TS: Focuses on minimizing loss of life and property.
• SS: Strives for sustainable ecosystems that balance flood benefits and risks to support flora, fauna, and human life.

The Need for a Transdisciplinary Approach

Flood risk management encompasses the following interconnected systems:

• Physical Systems: Climate extremes, sedimentation, and ecological dynamics.
• Socioeconomic Systems: Investment priorities, social norms, and economic objectives.
• Human Systems: Political ambitions, cultural behaviors, and informal settlements.

To address this complexity, a transdisciplinary approach integrates knowledge across natural sciences, social sciences, mathematical modeling, and indigenous wisdom. It involves collaborative problem-solving among academics, professionals, government, and civil society, ensuring solutions are:

1. Physically viable.
2. Ecologically sustainable.
3. Economically sound.
4. Socially justifiable.
5. Politically acceptable.

Adaptive Planning in Flood Risk Management
Unlike static master plans, adaptive planning is iterative and responsive, evolving as new insights and conditions emerge. Plans are refined through continuous learning and feedback.

Sample Roadmap for Adaptive Planning:

1. Initial Appraisal: Assess flooding problems and issues across metro, urban, or basin areas.
2. Comprehensive Evaluation: Examine watersheds, land use, and drainage systems with stakeholder input.
3. Simulation and Solutions: Conduct hydrologic, ecological, and economic simulations to identify optimal solutions.
4. Project Implementation: Prioritize and sequence projects based on time, cost, and evolving water regimes.
5. System Reassessment: Monitor the performance of flood mitigation systems and adapt to changing conditions.
6. Solution Updates: Revalidate and reprioritize projects to align with updated flooding patterns and socio-economic dynamics.

This adaptive and collaborative framework ensures flood management strategies remain effective and sustainable amid changing environments.

Flood Mitigation Planning Decision Tree

The flood mitigation planning decision tree offers a structured framework for managing flood risks, consisting of three key strategies:

1. Restore: Reinstating Natural Features and Processes
    This approach emphasizes bringing back natural landscape features, such as floodplains, wetlands, and forests. These restored ecosystems act as natural sponges, slowing down and storing floodwaters while mitigating flood risks.
2. Enhance: Modifying or Enhancing Natural Systems
    Enhancing natural features and processes improves their efficiency in managing floods. For instance, modifying wetlands or strengthening riverbanks can amplify their ability to reduce water flow intensity and store excess water.
3. Engineer: Implementing Engineered Flood Protections
    When natural or enhanced solutions alone are insufficient, engineered interventions like floodwalls, embankments, and storage reservoirs are introduced. These structures are skillfully designed to safeguard urban areas and critical infrastructure from severe flooding.

Flood Control and Coastal Resilience with Nature-Based Solutions

Nature-based solutions are increasingly being integrated with traditional engineering to address flood risks and enhance coastal resilience. These approaches are categorized into:

• Natural Solutions: Restoring ecosystems such as floodplains, wetlands, and forests to manage floodwaters. These features naturally absorb and attenuate water flow, reducing flood intensity.
• Hybrid Solutions: Combining natural and engineered elements to amplify the effectiveness of flood mitigation. For example, levees may be paired with restored wetlands to enhance water storage and flood risk management.
• Engineered Solutions: Traditional infrastructure like floodwalls, embankments, and reservoirs are designed to protect urban areas from floodwaters.

In urban flood control, nature-based solutions play a vital role in reducing stormwater runoff, replenishing groundwater, and providing alternative water sources such as brown water. Along coastlines, these solutions strengthen resilience by creating buffers against storm surges, erosion, and rising sea levels, ensuring a balanced approach that benefits both human settlements and ecosystems.

By blending natural, hybrid, and engineered strategies, this integrated framework fosters sustainable, adaptive, and effective flood risk management.

West Manggahan Flood Mitigation Project

In Metro Manila, floodwaters from the Marikina River are typically diverted to Laguna Lake via the Manggahan Floodway for temporary storage, rather than flowing directly into Manila Bay. However, following the construction of the Manggahan Floodway in 1982, flooding events in the northern lakeshore towns of Taguig and Taytay became more frequent. In response, the government proposed the development of a road-dike system designed to shield these towns from further flooding.

Despite this proposal, the plan faced significant opposition from various stakeholders, including fisherfolk, farmers, business owners, and residents of the lakeshore communities. They raised concerns over the proposed alignment and configuration of the lakeshore dike, especially regarding its environmental impact. To address these concerns, a transdisciplinary approach was adopted, facilitating eight stakeholder consultations. These consultations resulted in six alternative configurations for the lakeshore dike. These alternatives were subjected to an interactive review process involving engineers, economists, and biologists to assess their feasibility.

The alternative configurations included:

1. Full protection of human settlements through polder dikes, which would unfortunately eliminate fish spawning areas.
2. Partial protection for human settlements while preserving fish spawning grounds.
3. A hybrid solution offering full protection for human settlements while also retaining the fish spawning area achieved through a combination of road dikes and bridges.

Flood inundation simulations, socio-economic surveys, and comprehensive analyses of social, environmental, and economic impacts were conducted to evaluate each alternative. Among the various configurations, Alternative 1B—partial protection of human settlements while retaining fish spawning areas—was selected based on its positive environmental impact and its favorable Economic Internal Rate of Return (EIRR) of 8.59%.

Cagayan de Oro River Basin: Flood Simulation Studies

The flood mitigation strategies for the Cagayan de Oro River Basin were explored through a comprehensive flood simulation model, which was presented alongside a map of the river basin. The model relied on governing equations for mass conservation of water-sediment mixtures and momentum conservation along both x- and y-axes of the flow.

Several flood mitigation alternatives were evaluated, including:

1. The existing flood control structures in place.
2. Flood control measures currently under construction.
3. Proposed flood mitigation projects by the DPWH-JICA, with two options—3a (low wall) and 3b (high wall).
4. A proposed realignment of the dike in the Paseo del Rio-Torre de Oo area.
5. Alternative retarding basins to manage floodwaters.
6. A combination of alternative retarding basins 1 and 2.
7. A proposal to use overflow weirs downstream of Pelaz Bridge for river flood storage, with or without the additional retarding basins.

These alternatives were evaluated for their potential to mitigate flooding, considering factors like efficiency, environmental impact, and cost.

Candaba Swamp: Ecological Value and Flood Control Detention

Candaba Swamp plays a crucial role in the region’s ecosystem, particularly as a natural flood detention basin during the wet season. To maintain the swamp’s ecological function, it is vital to preserve its historical flood inundation patterns, which regulate seasonal wet and dry cycles in the floodplain.

To enhance flood control, a network of detention ponds or impoundments could be developed to store excess floodwaters, which could also be utilized for water supply purposes. Maps illustrating the Candaba Swamp area from October 2012 to October 2022 showed the extent of flood inundation over time, highlighting its role in flood storage and its capacity to act as a natural buffer against flooding.

Pasig-Marikina River Basin Flood Mitigation

The Manggahan Floodway, which aims to alleviate flooding in the Pasig River basin, diverts floodwaters from the Marikina River to Laguna de Bay, a temporary reservoir. This diversion helps reduce the impact of peak floodwaters along the Pasig River. The floodway was initially designed to work in tandem with the proposed Parañaque Spillway, which would direct water from Laguna de Bay into Manila Bay. However, the spillway project was ultimately canceled.

Completed in 1986 at a cost of 1.1 billion pesos, the Manggahan Floodway remains a critical component in the region’s flood mitigation strategy.

Marikina River Flood Tunnel/Channel Proposal

To further enhance flood control in the region, a proposal has been made to construct a flood tunnel or channel to divert 30-40% of the Marikina River’s flow directly into the Pacific Ocean. This diversion would help reduce pressure on both the Pasig River and the Laguna Lake, ensuring that these bodies of water are better able to manage floodwaters. The diversion point is proposed at the Tayabasan-Montalban-Sapa Bute Bute junctions, covering an area of 180 km².

Iloilo Flood Control Project

The Iloilo Flood Control Project, proposed in 1995 and completed in 2010, was designed to address flooding in Iloilo City, particularly after a series of severe floods in the 1990s. The project, which cost 6.06 billion pesos (approximately 12.84 billion yen), was designed to handle a flood event with a return period of 20 years. Flooding in July 1994 and from 1998 to 2001, which affected over 120,000 households, underscored the urgent need for such a project.

SMART (Stormwater Management and Road Tunnel) in Kuala Lumpur

The SMART project in Kuala Lumpur, Malaysia, is a unique infrastructure development that integrates stormwater management and road transport. The 13.2-meter diameter tunnel features a 9.7 km stormwater bypass tunnel and a 4 km dual-deck motorway for light vehicles. The project was designed to address flash flooding caused by the Sungai Klang and Kerayong rivers and to alleviate traffic congestion during peak hours.

Construction began in 2003, and the tunnel was opened in May 2007, costing around $514 million (approximately 25 billion pesos). During its operation, the SMART tunnel has significantly reduced flooding in Kuala Lumpur while also improving traffic flow.

Nonstationary Extreme Value Analysis for Flood Design

In flood control projects, determining the design storm magnitude and its associated return period is a critical parameter. Traditionally, it has been assumed that the probability distribution of extreme weather events is stationary over time. However, with the impacts of climate change, it is necessary to treat these extreme events as nonstationary.

The Department of Public Works and Highways (DPWH) in the Philippines has applied nonstationary extreme value analysis to several major flood control projects, including those in Laoag, Agno, Pampanga Delta, KAMANAVA, Pasig-Marikina, Manggahan Floodway, Iloilo, Agusan, and Ormoc.

An example of this approach was demonstrated with Cagayan de Oro River, where the return period of the peak flow during Typhoon Sendong in December 2011 was calculated using both stationary and nonstationary methods. The stationary analysis indicated a return period of about 90 years, while the nonstationary analysis reduced the return period to 15 years, reflecting changes in rainfall patterns and urbanization. This methodology helps ensure that flood control structures are designed to withstand more frequent and severe extreme events due to climate change.

 Session Two: Government Flood Control Plan

Resource Person:
Jerry Fano
Flood Control Cluster
Department of Public Works and Highways (DPWH)

Jerry Fano, representing the DPWH Flood Control Cluster, provided an in-depth overview of the government’s flood management initiatives under the Unified Project Management Office. His presentation delved into both structural and nature-based solutions designed to mitigate flooding across various vulnerable regions in the Philippines.

Structural Measures for Flood Control

Fano detailed the engineering strategies employed in flood control projects. These include the construction of dikes, designed with a height that exceeds the design flood level by incorporating a freeboard. Gravity walls reinforced with concrete bases, toe protection systems, and revetments equipped with cut-off walls and aprons to protect riverbanks from erosion are among the key measures implemented. Additionally, grouted riprap and spur dikes enhance these protective systems, safeguarding communities and infrastructure from rising waters.

Nature-Based Solutions (NBS)

Fano emphasized the importance of harnessing nature’s innate ability to regulate flooding. Using vegetation buffer strips, for example, can reduce water velocity in flood-prone areas, prevent soil erosion, and promote nutrient deposition in agricultural lands. NBS also includes sustainable practices like smart riverbed quarrying to maintain river stability.

Room for the River Approach

Acknowledging the natural behavior of rivers, this approach involves respecting and accommodating floodplains. By preserving the space required for rivers to flow and transport sediment, human interventions are minimized, reducing flood risks while maintaining ecological balance.

Reforestation and Afforestation Efforts

Reforestation has become a cornerstone of flood mitigation, with initiatives focused on stabilizing watersheds, strengthening coastlines with mangroves, and reinforcing floodplains with vegetation buffers. Fano outlined three key submeasures:

1. Watershed Stabilization: Enhancing vegetation cover on hillslopes to minimize landslides.
2. Coastline Strengthening: Planting mangroves to shield coastal areas from storm surges.
3. Floodplain Reinforcement: Slowing floodwater velocity with strategically placed vegetation.

Afforestation processes complement these efforts, aiming to create new forested areas in regions devoid of vegetation to boost ecological resilience and reduce flooding.

Current and Future Initiatives

Major River Basins (MRBs)

Fano provided updates on ongoing projects in the Philippines’ 18 major river basins (MRBs), each representing a critical component of the government’s comprehensive flood control strategy.

Cagayan River Basin

• Regions Covered: II, III, CAR
• River Length: 520 km
• Catchment Area: 27,493 sq. km
• Current Initiative: Updating the master plan and pre-feasibility studies with financing from JICA (May 2024–October 2025).
• Notable Projects: Completed revetment works in the Albago and Cataggaman areas following Typhoon Ramon.
• Future Initiative: Detailed engineering design and feasibility studies for long-term flood management solutions.

Abra River Basin

• Regions Covered: I, CAR
• River Length: 181 km
• Catchment Area: 4,936 sq. km
• Current Initiative: Development of a master plan and feasibility study, financed by ADB.
• Structural Measures Proposed: Reinforced gabion walls, spur dikes, and toe protection totaling over 45 units.
• Non-Structural Measures: Reforestation, early warning systems, and strengthened institutional capacity.

Pampanga River Basin

• Regions Covered: III
• River Length:33 km
• Catchment Area: 9,759 sq. km
• Current Initiatives: Updating the master plan and feasibility studies, with structural designs including an 89.2 km diking system and 21 culverts with control gates.
• Future Initiative: Construction of a Central Luzon-Pampanga River Floodway (estimated cost: Php 115 billion).

Agno River Basin

• Regions Covered: I, II, III, CAR
• River Length: 206 km
• Catchment Area: 5,747 sq. km
• Current Initiative: Feasibility studies financed by ADB (2023–2026).
• Future Initiative: Civil works estimated at Php 12 billion, incorporating dikes and smart quarrying practices.

Pasig-Marikina-Laguna Bay Basin

• Regions Covered: NCR, IV-A
• River Length:2 km
• Catchment Area: 3,280 sq. km (Laguna de Bay), 635 sq. km (Pasig-Marikina River)
• Current Initiative: Phase IV channel improvement works, including revetment construction and drainage enhancements.
• Future Initiative: Proposed construction of three dams in the Upper Marikina, retention ponds, and additional river improvements.

Comprehensive Overview of Key Flood Management and Risk Mitigation Projects in the Philippines

1. Prañaque Spillway/Tunnel Project (JICA ODA)

This ambitious project, designed to mitigate flooding across Metro Manila and Cavite, spans key urban centers, including Muntinlupa, Parañaque, Las Piñas, and Bacoor City. The project involves the construction of an open channel and tunnel (Route X), stretching 10.5 km from Buli (intake location) to Manila Bay (outlet location).

Key Specifications:

• Total Project Cost: Php 105.701 billion
• Timeline: 2026–2036
• Current Status: Feasibility study and preparatory survey completed.
• Details:
  • Open channel and jetty: 0.8 km
  • Tunnel length: 9.7 km, with a depth of over 50 meters
  • Tunnel inner diameter: 13 meters
  • Vertical shafts at intake and outlet: 75 meters high
  • Maximum outflow discharge: 240 m³/s

2. Flood Risk Management Project (Cagayan, Tagoloan, and Imus Basins)

JICA Loan Agreement No. PH-P253
 This project includes the Imus and Bacoor Retarding Basins to mitigate flooding in Cavite.

Sub-Project Components:

• Imus Retarding Basin:
  • Area: 35 hectares
  • Overflow dike: 118 meters long
  • Volume: 2,101,700 m³
• Bacoor Retarding Basin:
  • Area: 9.01 hectares
  • Overflow dike: 42 meters long
  • Volume: 313,700 m³
• Drainage Sluices: Two locations.

Milestones:

• Imus Retarding Basin was completed between April 2022 and 2023, along with a water treatment facility and sections of the Bacoor Retarding Basin.

3. Metro Manila Flood Management Project, Phase I

This initiative addresses flooding in the National Capital Region through structural and non-structural measures.

Project Details:

• Total Cost: Php 23.50 billion
• Timeline: 2018–2026
• Financing: IBRD 8784-PH and AIIB 000023-1 PH

Structural Measures:

1. Rehabilitation of pumping stations (PS):

• Batch 1: Balut, Vitas, Paco, Labasan, and Tripa de Galina.
• Batch 2: Libertad, Makati, Sta. Clara, and San Andres, among others.
• Batch 3: Acacia, Niugan, Muzon, and more.

4. Flood Risk Management in Major River Basins (MRBs)

1. Panay River Basin (Region VI)

Scope: Updates to the master plan and feasibility study for flood control.

• Current Initiatives:
  • Updating plans (2022–2024) funded by KEXIM at Php 308.068 million.
  • Detailed engineering design (2025–2026) at Php 299 million.
• Future Civil Works:
  • Diversion channels, dikes, drainage facilities, and resettlement plans are estimated at Php 9.34 billion.

1. Cagayan de Oro River Basin (Region X)

• Completed Measures:
  • Construction of dikes, drainage outlets, and resettlement sites.
  • Total cost: Php 12.538 billion.
• Design Standards: Structures are built to withstand a 50-year flood return period.

1. Davao River Basin (Regions X and XI)

• Current Plans:
  • Riverbed dredging, construction of cut-off channels, and retarding ponds.
  • Feasibility studies (2025–2026) led by JICA.
• Future Initiatives: Php 41.72 billion proposal for civil works (2029–2036).

1. Buayan-Malungun River Basin (Regions XI and XII)

• Ongoing Initiatives:
  • Master plan and feasibility study completed in 2024, funded by ADB for USD 31.36 million.
  • Detailed engineering design (2024–2026) under Phase 2 of the Integrated Flood Resilience and Adaptation Project (InFRA2).
• Future Projects: Civil works estimated at Php 7.80 billion (2028–2032).

1. Agusan River Basin (Regions XI and XIII)

• Plans: Diking and slope protection work spanning 43.4 km, complemented by flood forecasting systems and resettlement efforts.
• Cost: Php 7.80 billion for future initiatives, targeting completion by 2034.

Session Three: Flooding and Urban/Rural Planning

Resource Person:
Asst. Prof. Carmelita Rosario Liwag
Assistant Professor, UP School of Urban and Regional Planning

Asst. Prof. Carmelita Rosario Liwag, a highly respected academic and licensed environmental planner from the University of the Philippines, led the session on flooding and urban/rural planning. With extensive experience in urban and regional planning, Prof. Liwag has played a pivotal role in addressing complex land use challenges across the Philippines. Her academic tenure includes key administrative roles, such as serving as college secretary, and she has been actively involved in developing practical solutions to the pressing issues of urbanization, zoning, and environmental sustainability.

Persistent Land Use and Zoning Issues in Metro Manila and Neighboring Provinces

Prof. Liwag began by examining the underlying causes of persistent land use and zoning challenges in Metro Manila and surrounding areas. She highlighted how these problems are deeply rooted in:

1. Rapid Urbanization: Unchecked population growth and urban sprawl have led to significant encroachments on natural waterways and floodplains.
2. Inadequate Infrastructure: Outdated drainage systems and insufficient flood control measures are ill-equipped to handle the growing demands of densely populated urban centers.
3. Geographic Vulnerability: Metro Manila’s location within a natural flood basin amplifies its susceptibility to flooding during heavy rainfall or typhoons.
4. Climate Change: Rising global temperatures exacerbate flooding by intensifying weather patterns, leading to more frequent and severe rainfall events.

Challenges in Flood Management and the Role of Local Governments

Prof. Liwag underscored the pivotal role of local government units (LGUs) in mitigating flood risks and ensuring sustainable urban and rural development. She called attention to the responsibilities assigned to LGUs under the Local Government Code, particularly in updating disaster risk reduction and management (DRRM) plans and comprehensive land use plans (CLUPs).

She identified several challenges faced by LGUs:

• Limited financial resources to implement large-scale flood mitigation projects.
• Insufficient technical expertise in DRRM planning and execution.
• Gaps in interagency collaboration, leading to fragmented approaches to flood management.

To address these issues, Prof. Liwag proposed several strategies:

1. Flood Management Master Planning

She presented Metro Manila’s flood management master plan, which includes both structural and non-structural measures. While large-scale projects such as the construction of dikes, floodways, and pumping stations are essential, she acknowledged the immense financial and logistical hurdles in realizing these plans.

2. Technological Integration

Prof. Liwag highlighted the transformative potential of Geographic Information Systems (GIS) and real-time flood forecasting systems in flood management. These technologies allow for:

• Mapping of flood-prone areas.
• Monitoring weather patterns and water levels.
• Providing real-time alerts to communities, enabling quicker and more effective responses.

3. Interagency Collaboration

She stressed the importance of seamless coordination among national agencies, LGUs, and non-governmental organizations to ensure cohesive and efficient flood mitigation efforts. Collaborative initiatives, she argued, are vital for sharing resources, knowledge, and expertise.

The Multifunctional Potential of Detention Ponds

A significant portion of Prof. Liwag’s discussion centered on the concept of detention ponds as a sustainable solution for managing stormwater runoff in urban areas.

1. Purpose and Functionality

Detention ponds are engineered to temporarily store excess stormwater during heavy rains, reducing the risk of flooding in surrounding areas. These structures are particularly effective in low-lying regions like Metro Manila, where traditional drainage systems are often overwhelmed.

2. Dual-Use Urban Infrastructure

Drawing on successful examples from industrialized nations like Japan and South Korea, Prof. Liwag showcased how detention ponds can serve multiple functions. In addition to their primary role in flood control, they can be designed as:

• Recreational parks during dry seasons.
• Green open spaces that enhance urban aesthetics and provide residents with areas for leisure and exercise.

She cited potential applications in Metro Manila, emphasizing how these facilities could improve the city’s livability while addressing flood risks.

3. Case Studies and Lessons Learned

• Japan: The Metropolitan Area Outer Underground Discharge Channel, a large underground flood control system in Tokyo, incorporates detention basins to manage stormwater effectively.
• South Korea: The Cheonggyecheon Restoration Project in Seoul transformed a neglected urban stream into a vibrant public space that also functions as a flood control measure.

Comprehensive and Collaborative Approaches to Flood Mitigation

Prof. Liwag concluded by advocating for an integrated approach to flood mitigation, combining technical, social, and environmental strategies. She reiterated the need for:

• Community Engagement: Educating residents about flood risks and involving them in decision-making processes.
• Policy Reform: Strengthening policies on land use, zoning, and disaster risk reduction to address current and future challenges.
• Sustainability: Ensuring that all flood mitigation efforts align with the principles of environmental sustainability and resilience.

Her presentation underscored the urgency of addressing flooding as a multidimensional issue that requires coordinated action across all sectors of society. As the session drew to a close, participants were left with a deeper understanding of the complexities of urban and rural planning and the critical steps needed to safeguard communities from the impacts of flooding.

Question and Answer Portion: Highlights and Insights

The Q&A session provided a platform for participants to delve deeper into pressing issues surrounding flooding, environmental sustainability, and community engagement. Moderators emphasized brevity to accommodate the range of questions, yet the discussion remained rich and multifaceted, addressing several critical themes.

The Role of Detention Ponds in Urban Areas

One of the key highlights was the discussion on the importance of detention ponds in flood-prone urban areas. A participant raised a question about their necessity, prompting an explanation of their role as vital infrastructures for managing stormwater runoff, particularly in low-lying areas during heavy rainfall.

Drawing from examples in industrialized countries like Japan and South Korea, the speaker illustrated how these ponds are effectively integrated into urban landscapes. Beyond flood management, detention ponds were highlighted for their potential to serve dual purposes, such as acting as parks or open spaces. In Metro Manila, their multifunctionality could enhance urban livability while addressing critical flood risks.

Sustainable Practices for Resilience

The conversation also touched on adopting sustainable materials and planting native trees to strengthen environmental resilience and mitigate flooding. Native tree species, noted for their durability during typhoons, were recommended for reforestation efforts, emphasizing their role in creating thriving riverine ecosystems and supporting local wildlife.

Additionally, the session discussed innovative infrastructure solutions, including replacing traditional road materials with porous alternatives to improve water drainage. Emerging technologies were highlighted as promising tools to enhance the environmental sustainability of urban development.

Plastic Waste Management and Urban Flooding

Plastic waste was identified as a significant contributor to flooding, particularly in urban areas like Taft Avenue in Manila. Participants praised ongoing initiatives to regulate plastic packaging and waste management but stressed the importance of public education on proper disposal practices.

A question about Taft Avenue’s long-term flooding solutions led to discussions on the area’s infrastructure, including concerns about the Dolomite Beach project. The need for effective stormwater management systems was underscored to address the persistent waste-induced flooding issues.

Water Management Strategies and Rain Harvesting

Participants explored water management strategies, with a focus on rain harvesting. The speaker emphasized its potential for flood control and groundwater recharge, highlighting the importance of providing region-specific guidelines to account for varying rainfall patterns across the Philippines.

Challenges such as acquiring land rights for river system management were noted, along with the critical need for proper land use planning to facilitate water infiltration and sustainable urban development.

Human Behavior and Cultural Practices

The conversation shifted to the significant role of human behavior in effective flood management. Despite advancements in infrastructure and technology, the persistence of waste disposal issues at pumping stations underscored the need for cultural shifts.

The session called for a change in individual waste management habits, emphasizing the importance of community involvement and education. Participants agreed that flooding solutions require not only technical interventions but also behavioral and cultural transformation.

Community Engagement and Collective Action

Finally, the session emphasized the importance of participatory planning processes and collective action. One participant raised the idea of utilizing school football fields as water cisterns, showcasing innovative resource management concepts.

The speaker encouraged varying levels of stakeholder engagement among local government units to ensure inclusive planning. The session concluded with a call to action for reducing carbon footprints and supporting environmental initiatives like the Green Convergence campaign.

Through this interactive session, participants gained a deeper understanding of the multifaceted approaches needed to address flooding and environmental challenges, underscoring the collective effort required for sustainable solutions.