Flood Protection

by Ronel Forbes

December 3, 2021

Flood Protection for Vulnerable Communities

Flood damage is uninsured in 70% of cases

Every one of the country’s approximately 125 million occupied dwellings. Flooding is a possibility in this area.

While over 7 million dwellings in the Philippines are at risk of flooding due to catastrophic storm surges, over 10 million more are at risk of flooding due to river overflows and flash floods. Unfortunately, many flood-prone homeowners are unaware of this.

The cost of flood damage to a typical home might easily reach ₱50,000. Following a flood, damaged homes are frequently unfit for occupation, displacing the homeowner and necessitating additional housing costs.

Furthermore, flood damage is frequently uninsured. This is largely due to the constitution’s requirements, which only apply to properties classified as being at the highest danger.

However, low risk does not imply no risk. As a result, more than 70% of the damage caused by floods is uninsured. Flood insurance coverage must be specifically suited to the complexity of flood risk.

A Complex Risk to Housing

Flooding can be caused by a variety of factors, including surface water flow, overflowing rivers, and coastal storm surge. When rain falls on the ground, the water collects and runs through the ground, eventually reaching rivers and other drainage paths, causing river floods downstream.

During a hurricane, the storm can force water from the ocean up the coast, generating substantial flooding upstream of drainage paths, known as storm surge. One widespread misperception concerning flood risk is that it is solely determined by a property’s elevation, however this is not always the case.

Typhoon Yolanda devastated the Eastern Visayas in 2013, leaving $4.5 billion in damage. It depicts the flooded neighborhoods in Eastern Visayas following Typhoon Yolanda. There were 100,000 people who were horrified to learn that their home was at risk due to flooding.

Homes in a Special Flood Hazard Area are classified by the government as having the highest flood risk (SFHA). This zone, often known as the 100-year flood zone, is defined as an area where the yearly risk of flooding is 1% per year.

Many homes outside of the SFHA, particularly those immediately outside the perimeter, are still at great danger of flooding.

When the SFHA is used as a flood risk indicator, it is assumed that homes outside of the SFHA are not at risk. A more subtle approach would be to build a risk gradient, with locations outside the SFHA having a slightly lower risk and areas inside the SFHA having a slightly higher risk.

As a result, we may incorporate the 50-year flood zone and the 500-year flood zone in our models to make them more realistic.

Flood Master Plan for Metro Manila

After Ondoy and Pepeng in 2009, the government, with the help of the World Bank, developed the Metro Manila Flood Management Master Plan in response to PDNA recommendations. The Master Plan provides a blueprint or roadmap for managing flood problems in Metro Manila and the adjacent areas over a 25-year timeframe.

It provides a complete flood risk assessment, describes a comprehensive flood risk management strategy, and suggests a set of prioritized structural and non-structural interventions to reduce Metro Manila’s vulnerability to damaging floods and increase its resilience.

Flood management dams, river improvements, and floodways are examples of structural or engineering solutions, while non-structural mitigation measures include land use regulations, watershed conservation, reforestation, and preparedness measures such as improving flood warning systems, rainfall and water level gauging stations, and information systems.

The master plan proposed a set of measures, including the following, to successfully handle large flood events:

Lower flooding from the city’s river systems by constructing a dam in the upper Marikina River catchment area to reduce peak river flows into Metro Manila during typhoons and other extreme rainfall events;
To safeguard the population living near the shore from high water levels in the lake, eliminate long-term flooding in the Laguna de Bay flood plain.
Improve urban drainage, including pumping station upgrading in Metro Manila; and
Flood forecasting, early warning systems, and community-based flood risk management are all in need of improvement.

Putting the Master Plan into Action

The Metro Manila flood master plan is now being implemented.

In the cities of Manila, Pasay, Taguig, Makati, Malabon, Mandaluyong, San Juan, Pasig, Valenzuela, Quezon City, and Caloocan, the project seeks to update 36 flood management pumping stations and construct 20 more, as well as supporting infrastructure along vital waterways. Many current pumping stations in Metro Manila were built in the 1970s and have since become inefficient and underperforming.

Solid garbage jams streams and pumping station entrances, causing problems with pump operation and maintenance. The project would improve solid waste management in barangays (villages) near pumping stations that serve drainage systems.

It will also assist the government in the resettlement of informal settlers living beside waterways.

The project costs US$500 million, with the World Bank contributing US$207.6 million, the AIIB contributing US$207.6 million, and the Philippine government contributing the remaining US$84.79 million.

The project is being implemented by the Department of Public Works and Highways (DPWH) and the Metro Manila Development Authority (MMDA) in close collaboration with local governments and important shelter agencies. By the end of 2024, the project should be completed.

Flood management in the Pasig-Marikina River Basin is being improved. Flood management infrastructure is required to temporarily hold floodwaters so that the remainder can be transferred into Laguna de Bay and Manila Bay without flooding metropolitan areas. A project to this aim is in the works, which will include a massive Marikina flood management dam and a retention basin between the Montalban and San Mateo Bridges, both of which were listed as priority structures in the Master Plan.

The flood control structures will not only safeguard lives and property, but they will also prevent riverbank erosion, which could undermine the bridge structure. With different cities as the province’s commercial and industrial hub, the completed project will help preserve agriculture, fisheries, and other agricultural resources, expanding the region’s economic opportunities,” Villar stated.

Causes and consequences of floods

Flooding can be caused by a variety of events, including heavy rain, strong winds over water, unusually high tides, tsunamis, dam failure, or elevation of retention pond levels or other water-containment facilities. Many rivers flood on a regular basis, generating an alluvial plain in the surrounding area.

During rain or snowfall, some of the water is kept in ponds or soil, while others are absorbed by grass and vegetation, while others evaporate, and the remainder moves over the ground as surface runoff.

When lakes, riverbeds, soil, and vegetation are unable to absorb all of the water, flooding occurs. Water then escapes from the land in volumes that are too large to be transferred into stream channels or held in natural ponds, lakes, and man-made reservoirs.

Small runoff accounts for about 30% of all rainfall, and the amount can be boosted by the water from melted snow where it exists. Heavy rains are the most common cause of river flooding, which can be exacerbated by snowmelt.

A sudden flood is defined as flooding that occurs suddenly and without notice. Heavy rains in a narrow region, or if the area was previously saturated with prior precipitation, frequently cause sudden floods.

Flooding can also be caused by strong winds blowing over water. Strong gusts, such as those experienced during hurricanes, can cause the shores of lakes and bays to be inundated, even when the rain is relatively mild.

Another factor is the occurrence of exceptionally high tides, which can occur in coastal areas when they are flooded by unusually high tides, particularly when they are accompanied by strong winds and storms.

Flooding has a wide range of consequences. They cause property damage and put humans and other living things in peril. Rapid water runoff produces soil erosion and silt deposition in a variety of locales, including fish breeding grounds and other wildlife habitats, which can become polluted or destroyed.

Floods that are very severe and last for a long time can wreak havoc on automobile traffic in regions without elevated roads. Flooding can cause problems with drainage, economic land usage, and agriculture.

Bridge pillars, sewage systems, and other structures in flood-prone areas might sustain structural damage. The use of water for navigation and hydroelectric power is frequently impeded.

Flooding causes annual financial losses in the millions of dollars.

The global economic impact was estimated at US$ 1.5 trillion, which included other industries besides agriculture and other types of natural disasters. Since 1980, the annual average of disasters has more than doubled. Floods, droughts, and storms have cost Latin America and the Caribbean an estimated US$ 11 billion in agricultural productivity, with floods accounting for 55 percent of the losses, with droughts and storms accounting for the rest.

Around 60% of the total estimated losses in developing countries over that decade – US$ 48 billion – were attributed to floods in countries such as India, the Philippines, and Pakistan.

Natural disasters resulted in the loss of 333 million tons of cereals, vegetables, meat, milk, and other commodities, according to the FAO. To address these trends, the FAO recommended that information systems on the impact of disasters on agriculture be improved, as well as advances in adaptive capacity and effect mitigation, as well as increased investment in the industry.

According to reports, water-related disasters account for 90% of all disasters in terms of the number of persons affected. According to speakers at the 8th World Water Forum’s High Level Panel on Water and Natural Disasters, social and economic costs have escalated in recent decades and would continue to climb if no action is taken.

Water-related natural disasters cost the global economy $ 306 billion in 2017. 90 percent of disasters between 1980 and 2016 were caused by climate change. Storms were responsible for 31% of global losses in 2016, followed by flooding (32%), and severe temperatures (10%).

Bottom line

After a flood, a country’s society and economy suffer in a variety of ways, including the loss of lives, vegetation, property, and infrastructure, implying that there will be fewer people on the labor force, less agriculture available for locals and exporting, and fewer businesses to contribute to the country’s economic development. People will be displaced in large numbers, with many of them becoming homeless and jobless.

To close this imbalance, the government will have to increase its spending. Food and materials to clean and reconstruct the country’s infrastructure may have to come from outside the country.

While some countries will volunteer to help, others will charge for their services, placing the supported country in debt and at a disadvantage economically.