A typhoon in Northern Luzon along with monsoon rains resulted in flooding in many parts of the country yesterday. The National Capital Region was at a standstill, yet again. People had to stay home. By now, flooding is a common occurrence during heavy rains. Along with all the problems that go with it.
In the last 50 years, numerous flood control projects have been initiated. To date, however, nothing seems to work in the long term. Flooding is seasonal, but the same goes for the success of these projects. And with climate change seemingly bringing on more rain than usual nowadays, there is great urgency for cities to initiate more effective projects for flood control.
Success is not impossible. I believe there are many lessons to be learned from the Netherlands, China, the United States, Japan, the United Kingdom, Italy, and our very own Bonifacio Global City (BGC). And presenting great potential are the ongoing rehabilitation of the Philippine National Railways as well as the construction of the Metro Manila subway.
The Netherlands is tops, in my opinion, when it comes to flood mitigation. But success required decades as well as massive investments in public infrastructure that included a system of dams, sluices, locks, dikes, and storm surge barriers. Metro Manila can adopt a similar integrated approach by constructing a series of flood barriers like dikes along coastlines and key waterways such as the Pasig River.
The US Mississippi River and Tributaries Project made use of levees, floodways, reservoirs, and channel improvements. Something can also be considered for the Pasig and Marikina rivers. Channel improvements, if still feasible, can be considered, and the construction of reservoirs or water impounding systems in strategic locations.
And similar to China’s Three Gorges project on the Yangtze River, smaller-scale dams and retention basins can be constructed upstream in the river systems feeding into the metropolis. These structures can help control water flow and reduce downstream flooding during heavy rainfall.
As for water impounding, the Tokyo Metropolitan Area Outer Underground Discharge Channel (G-Cans) is said to be the world’s largest underground floodwater diversion facility. And this is where the Metro Manila subway project comes in. The 33-kilometer, 17-station subway, which will stretch from Valenzuela City to Parañaque City, is receiving Japan development assistance.
The subway project presents an opportunity to also transform the city’s drainage infrastructure and mitigate flooding. Subway construction can be integrated with flood control measures to create a dual-purpose system like Tokyo’s G-Cans. As subway tunnels are built, perhaps there is a way to add underground tunnels and storage tanks that can temporarily hold excess rainwater to prevent surface flooding. Flood waters can be released into rivers once the flood risk subsides.
Anyway, subway stations and tunnels will surely be equipped with flood control gates and pumping systems. These can be activated during heavy rain to prevent water from entering the subway and surrounding areas. Perhaps the same system can also help divert surface rainwater into underground impounding tunnels, and to pump them out when floods subside.
In Italy, mobile gates were built to protect Venice from flooding during high tides. We have something similar in place along the coast facing Manila Bay as well as parts of the Pasig River. But perhaps we need more of these so-called flood gates, against storm surges and high tide, as well as more drainage exit points into the river that can be closed and opened as necessary.
The United Kingdom has something similar called the Thames Barrier, which protects London from flooding. Of course, other than construction, regular maintenance and operational readiness will be crucial for these systems’ success. Maintenance and control may be centralized or localized but coordinated.
It goes without saying that any of these initiatives will be practically useless unless there is comprehensive work done to rehabilitate and improve drainage systems, considering present and future needs. Longer-term strategies are needed for sustainable drainage management, and this will necessarily require increasing the capacity of upgraded drainage systems.
On the part of local governments and the private sector, new construction should require green infrastructure solutions such as permeable pavements, green roofs, and rain gardens. These can help absorb rainwater, reduce runoff, and mitigate flooding. Homes and businesses should be encouraged to properly harvest rainwater and use it for non-potable purposes.
In a way, Bonifacio Global City (BGC) helped show the way by putting in place a drainage system designed to handle heavy rainfall. The system includes large underground drainage pipes and retention basins that can store excess rainwater temporarily. BGC’s Burgos Circle, I believe, has a big retention basin underneath. BGC also provided for green spaces that absorb rainwater and reduce surface runoff.
And, while the government is rehabilitating the national railroad, perhaps it can also consider using railroad rights of way as water impounding areas for flood management. This strategy leverages existing infrastructure to create additional flood control measures without requiring extensive land acquisition. Areas alongside tracks can be dug and converted into covered canals as water impounding areas.
Anyway, railroad rights of way often include buffer zones. For areas already lost to urban migration, they need to be reclaimed and cleared of illegal settlers. These areas are typically linear and can be engineered to hold significant volumes of water during heavy rain. The challenge, however, is ensuring the stability of the railroad tracks and building drainage systems that can overflow without disrupting train operations.
Bottomline, by repurposing existing railroad rights of way, Metro Manila can create additional water storage capacity without the need for extensive land acquisition, which is often challenging in densely populated urban areas. Water impoundments along railroad tracks can capture and store excess rainwater during heavy downpours, reducing the risk of flooding in adjacent areas. Building drainage canals alongside railroad tracks may also be easier to do than digging up existing roads.
Marvin Tort is a former managing editor of BusinessWorld, and a former chairman of the Philippine Press Council
