Monterrazas de Cebu has defended its flood-control system amid growing scrutiny over the development’s ability to handle extreme rainfall, saying no drainage system can realistically be expected to withstand a single worst-case storm comparable to Typhoon Ruping.
Ranel Pelpinosas, the development’s construction head, said Monterrazas designed its drainage facilities based on rainfall intensity, duration and frequency, as well as the property’s terrain and expected runoff.
He said the project went beyond the minimum requirements in its approved permits, with the drainage system designed at three times the required capacity under the applicable storm-drainage standards.
The explanation comes after Cebu City Vice Mayor Tomas Osmeña questioned whether Monterrazas’ detention ponds could contain runoff from an extreme rainfall event.
During a September 15 City Council discussion, Osmeña presented his own calculation that a Typhoon Ruping-scale rainfall over the roughly 118-hectare property could generate more than 300,000 cubic meters of water. His estimate was not adopted by the council as an official engineering finding, and the City Council later returned the Technical Infrastructure Committee report for further technical review.
Historical technical references cited in the latest report put the highest one-day rainfall recorded at Mactan during Typhoon Ruping in November 1990 at 276.1 millimeters.
Monterrazas, meanwhile, said its flood-mitigation system consists of multiple detention ponds serving separate catchment areas rather than one large basin covering the entire development.
In one roughly 20-hectare catchment, seven detention ponds have a combined capacity of 27,483 cubic meters, compared with a stated requirement of 8,220 cubic meters for that catchment.
Across the 118-hectare development, the developer said there are 24 detention ponds with a combined capacity of about 62,710.5 cubic meters, against a required capacity of 26,701 cubic meters under the approved drainage and flood-mitigation design.
The developer explained that runoff is designed to move through a series of ponds as individual basins fill. The system temporarily stores stormwater and releases it gradually rather than allowing a large volume of runoff to rush downhill at once.
Monterrazas General Manager Marie Camille Bondad also said the company regularly dewaters the ponds after rainfall to restore their available storage capacity. According to the developer, water is released gradually through a storm pump, with the final pond discharging toward the public drainage system in a controlled manner.
The company said it also operates two weather stations within the development and monitors rainfall conditions. Its drainage design uses a 50-year return period, according to Pelpinosas.
The controversy is not limited to the size of the detention ponds. Cebu City Council members have also questioned the technical basis for the 26,701-cubic-meter requirement, how the larger 62,710.5-cubic-meter capacity was calculated and what would happen if an extreme rainfall event overwhelmed the system.
The council therefore returned the Technical Infrastructure Committee report for further review rather than adopting its recommendation concerning the development’s ongoing activities.
Monterrazas said around 53 hectares of the property have already been completed, while roughly 28 hectares are undergoing development and another 37 hectares remain undeveloped. The developer said additional detention facilities have been considered for future phases.
The company also said it is willing to cooperate with further government inspections and provide additional technical information as the city continues reviewing flood risks in the area.
At the center of the debate is a larger question about Cebu’s drainage and watershed system: whether individual developments should be assessed only according to their own approved engineering requirements or also according to the combined effect of runoff from multiple developments and downstream drainage constraints.
For now, the City Council’s technical review remains pending, leaving the adequacy of Monterrazas’ flood-mitigation system under continued scrutiny as Cebu examines how its urban development can cope with increasingly challenging rainfall events.
