Sponge City

The floods we endured over the last two weeks elicited a hopeful press release from BBM.

According to the Philippine Information Agency, BBM identified 39 potential sites for rainwater catchment and underground detention structures in Metro Manila.

Apparently, they have already hired the Dutch engineering consultancy firm Royal HaskoningDHV to provide technical assistance and engineering design to build the facilities.

They are supposedly completing the study by this week.

Funding for the construction of these underground cisterns and retention ponds will be through a loan from the Beijing-based Asian Infrastructure Investment Bank (AIIB) alongside a counterpart fund from the Philippine government.

Once the engineering designs are completed and local government approvals (such as permissions to excavate fields at UP, Camp Aguinaldo and Miriam College) are secured, the government will open the actual procurement and bidding process for construction companies.

The estimated construction timeline for the underground rainwater catchment projects ranges from six months to 1.5 years per site, depending heavily on the scale and engineering complexity of each location.

The DPWH will prioritize the 39 sites based on flood vulnerability, physical accessibility and local government clearance.

Why AIIB? The multilateral bank has a corporate mandate requiring over 50 percent of its annual approvals to go toward climate-adapted “Green Infrastructure.”

The rainwater impounding and “Sponge City” concept which relies on nature-based solutions to capture and slow down water, matches the AIIB’s specialized financing criteria.

The AIIB is also already the co-financier (alongside the World Bank) of the ongoing Metro Manila Flood Management Project. Yes, there is such a project.

The Metro Manila Flood Management Project is a massive, $369.88 million (approx. P22.1 billion) co-financed initiative approved in 2017. It is jointly funded by AIIB and the World Bank.

The project is now in its critical final stretch and facing a hard deadline. The international financing agreement will expire on Nov. 30, 2026.

The World Bank and AIIB currently maintain a polite “Moderately Satisfactory” rating for its implementation after years of severe gridlock, typical of Philippine projects.

As of mid-2026, 19 out of the 34 targeted pumping stations have been fully modernized and rehabilitated. Progress on the proposed new pumping facilities has been seriously delayed. None of the planned four new pumping stations were operational when we needed them last week.

As usual, our officials blame the delay on persistent right-of-way disputes and local utility relocation issues. Bureaucratic incompetence is likely the more serious problem.

Due to years of slow fund disbursement and procurement bottlenecks, the Philippine government formally cancelled $2 million of the loan proceeds ($1 million each from the World Bank and AIIB) to slice off unreachable targets before the expiration date. Sumuko na!

Then again, those pumping stations will be rendered inoperable by garbage soon after they start using them. The garbage issue must be addressed first.

How effective is the Sponge City concept?

Cities abroad that tried it found it effective for moderate-to-heavy seasonal rains. The concept aims to shift away from concrete pipes to move water out. Instead, it uses nature-based, water-absorptive green infrastructure to capture, store, and slow down rain where it falls.

When correctly implemented as a comprehensive, city-wide network, a well-designed network of rain gardens, green roofs and permeable pavements can reduce surface runoff by 25 percent to 69 percent and delay peak flood flows.

Facing similar low-lying, flood-prone realities as Metro Manila, Bangkok transformed heavily paved urban land into the Benjakitti Forest Park. This massive green space acts as a natural urban sponge, capable of holding up to millions of liters of monsoon runoff while naturally filtering the water.

In the Philippines, individual components of sponge city infrastructure have been tested and proven effective on a micro-scale. The country has never tested a unified, city-wide public “Sponge City” network.

The most successful and frequently cited test case of subsurface water retention in the country is the Burgos Circle Cistern in Bonifacio Global City, which Metro Pacific, under the leadership of Manny Pangilinan,  built before the Ayala takeover.

Built in the mid-2000s, this 22-million-liter underground tank has kept the surrounding commercial hub virtually flood-free for over two decades. It has inspired BBM’s rollout of similar facilities across the 39 newly targeted sites.

The other development is the Vertis North Rain Garden in Quezon City, which features a two-hectare integrated urban park designed explicitly as a stormwater catchment system.

At Vertis, rainwater is caught by infiltration stripes (vegetated sidewalk bands) that pull water away from paved walkways and filter it down into perforated subsurface pipes. The runoff accumulates in a central detention pond and is slowly discharged into nearby creeks only when water levels are safe. The system has successfully prevented localized waterlogging inside the complex.

The Quezon City local government under Mayor Joy Belmonte has just opened the 651-cubic-meter retention and detention pond inside Quezon Memorial Circle. This functions as a multi-purpose scenic park during dry days but behaves like a micro-sponge during monsoons, like the last one, capturing runoff and routing it to dedicated tanks for city street-greening and plant-watering.

But as always, we can’t keep our hopes high that DPWH can implement and deliver quickly. As it is, DPWH is already pointing out that the civil engineering and construction market in the Philippines does not possess enough highly specialized contractors capable of simultaneous, complex deep-subsurface excavations.

Standard local contractors only own basic earth-moving gear. Executing subterranean concrete vaults (like the BGC model) requires specialized machinery. A fast-track rollout may dilute quality, DPWH claims.

So, while it is good to hear BBM trying to speed up the only flood mitigating deliverables he can offer in the last two years of his term, right now it is still just a press release designed to soften public anger brought about by the floods in recent weeks.

Boo Chanco’s email address is [email protected]. Follow him on X @boochanco