Licensed environmental planner Niceforo N. Iroy stated that the Cebu City Council's ongoing investigation into the Monterrazas de Cebu development has resulted in an inconclusive debate over opposing runoff and pond capacity numbers.
Iroy calculated that a storm matching typhoon Ruping's rainfall would generate between 228,832 and 294,212 cubic meters of actual surface runoff from the 118-hectare hillside estate.
Iroy urged for a complete rainfall-to-drainage simulation rather than relying on storage comparisons, noting that meeting government storage requirements does not automatically ensure downstream communities are safe from flooding
AS THE Cebu City Council’s investigation into the Monterrazas de Cebu development stretches into its second year, a licensed environmental planner says the whole debate has boiled down to a numbers fight that doesn’t actually prove anything — and it’s time to look at the real science instead.
In a technical opinion posted on Facebook, Niceforo N. Iroy, a licensed environmental planner and formerly with the Cebu City Planning and Development Office, broke down the math behind the arguments both sides have been making.
Vice Mayor Tomas Osmeña has warned that during an extreme storm — like typhoon Ruping of 1990 — runoff (rainwater that flows over the land instead of soaking into the ground) from the 118-hectare hillside estate could reach more than 300,000 cubic meters. Meanwhile, the city’s Technical Infrastructure Committee has pushed back, saying the development’s flood-control ponds can already hold 62,710.5 cubic meters, and soon 76,230.5 cubic meters — more than double the 26,701 cubic meters the Environmental Management Bureau (EMB) 7 originally required.
Checking the numbers
Iroy’s own calculations show Osmeña’s concern isn’t unreasonable. If a storm dumped as much rain as typhoon Ruping did — 276.1 millimeters in one day — across the entire 118-hectare property, that would add up to about 326,902 cubic meters of rainfall total.
But Iroy points out an important distinction: not all rainfall becomes runoff. Some of it soaks into the soil, gets absorbed by plants, or is slowed by the shape of the land. Using standard engineering estimates for how much rain actually turns into surface runoff, he calculates the real number is likely somewhere between 228,832 and 294,212 cubic meters — still a large amount of water, but different from the figure either side has been using.
Why neither number settles the debate
According to Iroy’s opinion, flood-control ponds, known as detention ponds, aren’t designed to hold all the rain that falls. Instead, they work more like a sink that’s filling up while the drain is open at the same time — they temporarily hold back the worst of a storm while steadily releasing water at a safe, controlled speed. Because of this, he says, simply comparing “how big the ponds are” against “how much rain could fall” is the wrong test — and so is claiming the ponds are fine just because they’re bigger than the minimum required.
What’s still missing, he says, are answers to these questions:
“What design storm and return period were used? What are the pre-development and post-development runoff hydrographs for each of the 14 catchments? What runoff coefficients or Curve Numbers were applied? What is the actual inflow into each pond? What are the pond outlet discharge rates? What is the time of concentration? What happens when the ponds reach maximum operating level? And, most importantly, can Kinalumsan, Linao and the downstream drainage network safely receive the combined controlled discharge during the same extreme rainfall event?”
The debate
In April 2026, the City Council cleared Monterrazas of primary blame, concluding that Guadalupe’s flooding came from multiple causes — including drainage limitations and water flowing in from other sources — not from any single development. Still, Osmeña warned that month that he would move to halt the project if severe flooding happened again, arguing that if the ponds aren’t big enough, they simply need to be made bigger.
By August, the council passed a resolution again pointing to multiple causes of flooding — including undersized pipes and clogged drainage systems citywide — while stopping short of halting the project, pending further technical study. That same month, a Guadalupe resident filed a complaint against Mayor Nestor Archival Sr., alleging a conflict of interest tied to a small property he and his spouse reportedly own inside Monterrazas.
The developer has continued submitting monthly compliance reports, including one noting zero water discharge from its ponds during a rainfall event in late July, and disclosing plans for a 14th pond. Most recently, on September 16, the City Council sent the technical committee’s report on Monterrazas back for further review, unsatisfied with its recommendation to let the project continue despite unresolved flood risks. It was this debate — over the 300,000-cubic-meter runoff estimate versus the ponds’ current capacity — that prompted Iroy’s technical rebuttal.
Technical opinion
Iroy’s opinion argues that the goal shouldn’t be to prove, ahead of time, that Monterrazas did or didn’t cause the flooding. Instead, he says, engineers need to run a complete rainfall-to-drainage simulation, tracing water from the sky, through all 14 catchment areas and ponds, and all the way downstream through the creeks and drainage network, under several conditions, including a worst-case extreme storm.
Meeting a government storage requirement and actually keeping downstream communities safe from flooding, he stresses, are related questions — but they are not the same question. That, he says, is why the report deserves a more complete technical review rather than a decision based on comparing two storage numbers. / MVG