San Miguel Corp. (SMC), through its unit San Miguel Aerocity, Inc. (SMAI), laid out the flood-mitigation measures and engineering studies behind the New Manila International Airport (NMIA) after online claims linked the Bulacan project to recent flooding.

SMAI, the airport's developer, said the claims surfaced following weeks of heavy rains. The company did not identify the individuals or groups behind the allegations or detail their basis. The dispute underscores the scrutiny facing one of the Philippines' largest infrastructure undertakings, which the government has positioned as a long-term answer to chronic congestion at Metro Manila's Ninoy Aquino International Airport.

"NMIA did not cause Bulacan's flooding. This is a problem the province has had to contend with for many generations. Our responsibility is to make sure the airport is built for these conditions, and that its development does not make flooding in the province worse," the company said in a statement on Thursday.

SMAI said the project was designed with long-term flood-mitigation measures intended to address risks to both the airport and surrounding communities. It attributed flooding in Bulacan to several factors, including the province's low-lying geography, heavy rainfall, upstream river flows, limited river capacity, land subsidence, rising sea levels, and continued development — conditions that also affect other low-lying coastal areas north of Manila Bay.

Engineering studies

Danish consulting firm DHI began research, engineering studies, and hydrological modeling for the airport project in 2018, according to SMAI. The studies examined surrounding rivers and coastal waters, historical typhoons and storm surges, land subsidence, and the possible effects of raising and developing the airport site on drainage and flood levels in surrounding and upstream communities.

DHI also conducted a river flood assessment and a broader Bulacan flood-mitigation study in 2019, which SMAI said identified the need for an engineered channel to improve water flow and mitigate flood risks associated with the project.

UK-based engineering firm Mott MacDonald later consolidated DHI's models and baseline data as part of efforts to align the project with international lender standards.

SMAI said long-term land-subsidence data and climate-change projections through 2100 were used to determine that the airport platform should be raised to between 3.85 meters and 5.5 meters above mean sea level at its center.

River works and cleanup

As the project moved into construction, Dutch marine engineering firm Boskalis and DHI developed an alternative to extensive river widening, SMAI said. The approach involved deepening riverbeds while narrowing their bottom width to achieve target flows, and was applied to the Maycapiz-Taliptip, or Alipit, River, the Santa Maria River, and the Meycauayan River.

SMC said it removed more than one million metric tons of silt and waste from the three rivers between 2022 and 2024. As of Aug. 18, it had removed more than 4.3 million metric tons of silt and waste from rivers across Bulacan under its river cleanup program.

SMAI also acknowledged that dredging alone might not be sufficient to address flooding during more severe rainfall, saying some areas could require additional structural interventions, including wider river channels, permanent river dikes, floodgates, and pumping stations.

"Protecting the airport and nearby areas and addressing Bulacan's larger flooding problems are two separate challenges," SMAI said.

"We can engineer NMIA for the conditions of the site and mitigate its impact. But protecting communities across Bulacan requires looking at the whole system — from the water coming from upstream, to the rivers carrying it, to the coastal areas where it eventually has to drain," it added.

SMAI said it would continue implementing environmental and flood-mitigation measures for NMIA while coordinating with government agencies and local governments on broader steps to improve river capacity and flood resilience in Bulacan. How the project balances site-specific engineering with province-wide flood management is likely to remain a point of public attention as construction progresses toward the targeted opening.

Project background

SMC, through SMAI, is developing the P740-billion NMIA on about 2,500 hectares in Bulacan. The airport is designed to accommodate up to 100 million passengers annually.

SMC has said the airport's commercial opening was pushed back to 2028 due to construction delays. In June, the company said the project's first runway was also expected to be completed by 2028.

On Thursday, SMC shares rose 50 centavos, or 0.79%, to close at P63.50 apiece. — Ashley Erika O. Jose