Engr. Rizel Rabaca stated that concrete drainage infrastructure accounts for only about half of the solution to Mandaue City's persistent flooding, noting that built networks cannot eliminate urban inundation alone.
Mandaue City's flood mitigation strategy stems from a Master Drainage Plan commissioned in 2017 with HydroNet Consultants, featuring proposed infrastructure projects carrying an estimated total cost exceeding P5 billion.
Rabaca emphasized that property owners must manage rainwater where it lands by installing rainwater harvesting tanks and utilizing permeable surfaces to prevent public road drains from being overwhelmed.
CONCRETE drainage infrastructure accounts for only about half of the solution to Mandaue City’s persistent flooding problems, requiring property owners and local authorities to adopt a broader approach to rainwater management.
Engr. Rizel Rabaca of the Mandaue City Planning and Development Office highlighted the limitations of relying strictly on concrete infrastructure. Without addressing surface runoff, river maintenance and private property development, built drainage networks will fail to eliminate urban inundation.
“These installations of drainage systems, that is just maybe 50 percent or around that — around that portion only to solve the flooding,” Rabaca stressed during his address. “It is not good that we rely 100 percent on the drainage system, thinking that if we complete our drainage, there will be no more floods. It does not work that way. There are larger factors at play.”
The multi-billion peso drainage blueprint
The City’s flood mitigation strategy stems from a Master Drainage Plan commissioned in 2017 with HydroNet Consultants, led by expert hydrologist Dr. Danilo Jaque. The master plan was divided into two distinct phases. Phase 1 rolled out in 2018 to address major city-level flooding along primary waterways, including the Banilad-Cabancalan Wetland, Basak Creek, Tipolo Creek and the Butuanon River. Phase 2 completed in 2020 and mapped out localized strategies for inner barangays to curb neighborhood-level inundation.
Proposed infrastructure projects across both phases carry an estimated total cost exceeding P5 billion based on 2018 to 2020 price calculations. This massive price tag underscores the scale of Mandaue’s civil engineering challenge, while illustrating that spending billions on underground concrete channels solves only part of the problem.
Why public road drains get overwhelmed
A major driver of recurring surface flooding is the mismatch between public infrastructure design and private development practices. Drainage networks constructed along public roads, including those managed by the Department of Public Works and Highways, are engineered primarily to handle water falling directly on the road itself.
Managing rainwater at the property level
Hydrologic principles show that rainwater must be managed where it lands rather than funneled into streets. Rabaca illustrated this concept through a typical micro-catchment setup: on a 200-square-meter lot featuring a 50-square-meter roof, installing a rainwater harvesting tank on the building captures roof runoff completely.
If the remaining 150 square meters use permeable surfaces — such as unpaved ground or porous pavers — along with an underground detention tank, the lot generates virtually zero excess runoff during heavy rains.
“If we have a property with a total area of 200 square meters, and we have a building or house where the roof area is 50 square meters, we put a rainwater tank there,” Rabaca explained. “For the remaining 150 square meters of our property, ideally, so that it does not generate runoff when it rains, we should make it permeable so it can absorb water. If we do that, our property will no longer contribute to the flooding.”
He added that if every property owner installed rainwater tanks and maintained permeable open ground, widespread street flooding could be largely prevented.
Upstream rivers and regional geography
Mandaue’s challenge is further complicated by regional geography. Serving as a lower discharge basin, the city receives high volumes of water originating from neighboring Cebu City’s elevated watersheds.
The Butuanon River stretches more than 23 kilometers from the uplands of Cebu City — passing through upper barangays such as Malubog, Bacayan, Sirao, Pulangbato, and Babag — before running a 10 to 11-kilometer stretch across Mandaue. Similarly, the Mahiga River carries upstream water past commercial areas toward outfalls at the Cebu Port Authority.
Because geographical position sends upstream water downward into the city, full flood mitigation requires strong solid waste management, continuous river desilting to clean heavy sediment and strict local ordinances regulating stormwater retention. Rabaca acknowledged that past urban development across Philippine cities often lacked strict stormwater regulation, but noted that policy adjustments can still fix current infrastructure gaps.
“Unfortunately, the direction of development in cities across the Philippines hasn’t always been proper,” Rabaca admitted. “It happened, but we still have time to correct it.” / DPC