Zamboanga City appears to have not learned lessons from Typhoon “Vinta” that in December 2017 unleashed heavy widespread rains across southern Philippines Mindanao islands resulting in 156 deaths, 291 missing, and 86 injured according to the Red Cross.
Leaving a widespread trail of devastation in a large area of the country, Vinta affected Zamboanga del Norte, Lanao del Sur, Bukidnon, Iligan, and Davao, where many of the fatalities were mostly due to drowning or buried in landslides. Ironically, Zamboanga City is no stranger to strong typhoons and flooding. Aside from Vinta, it was also hit by Super Typhoon “Paolo” in the same year. The city also experienced similar devastation from Super Typhoon “Pablo” in 2012, Severe Tropical Storm “Paeng” in 2022, and also the flooding caused by monsoon rains in August 2023.
This recent flooding was caused by torrential rains from July 11 to 13, followed by intermittent rains from July 14 to 15. According to the local weather bureau, the heaviest downpour was on July 12, at 170.2 millimeters in just 24 hours. Some 98 barangays experienced flooding, landslides, and rockslides. The floods killed six people, two were buried by landslides, and 18,358 individuals were displaced from their homes. This raises an unavoidable question: Given Zamboanga’s experience with typhoons and floods, why wasn’t the city’s flood control infrastructure better able to withstand the typhoons and the floods?
Is it because of a lack of understanding of how to manage floods or an over-reliance on traditional grey infrastructure solutions? I would venture it’s both.
As the impacts of climate change have become increasingly evident, local governments like Zamboanga City need to better understand floodplains and stormwater management systems if they are to mitigate flood hazards. Floods are part of the Earth’s natural hydrological cycle, which maintains an overall balance between water in the air, on the surface, and in the ground. Sometimes the hydrological cycle gets out of balance, as what happens during typhoons, sending more water to an area than it can normally handle. Rivers, creeks, and lakes will periodically overflow their banks and inundate adjacent land areas. The result is a flood that inundates a floodplain. Flood damages occur only when human beings interfere with the natural flooding process, such as altering the watercourse, developing areas in the upper watershed, and building in the floodplain itself.
The basic goal of floodplain management is not to prohibit development in floodplains but rather to guide development in floodplain areas in such a way as to greatly lessen the economic losses and social disruption caused by flooding events. It involves mapping out and defining the floodplain, the floodways within it, and base flood elevations. Based on these, measures are then promulgated to regulate development within the floodplain. For example, no buildings should be constructed within the floodway, and the ground floor of houses within floodplains should be constructed at least 1.20 meters above the base flood elevation.
A related tool is stormwater management, or the process of controlling the rainwater that runs off primarily from imperious surfaces like streets, parking lots, driveways, and rooftops. Rural areas are typically comprised of pervious areas, such as farmlands, pastures, and forests. These areas absorb and infiltrate the rainfall and generate a small amount of runoff. In contrast, urban areas typically contain a large percentage of impervious surfaces, such as pavements and rooftops. The quantity of runoff from these areas quickly overwhelms creeks and rivers, causing localized flooding, and property damage.
These two management tools can be reinforced and implemented through the local government’s land use plan and zoning ordinance, a local building code, as well as the local disaster risk reduction and management plan and local climate change adaptation plan. What is critical is to overcome the mindset that sees hard engineering and gray infrastructure as the only form of flood control, which includes changing university curricula and engineering handbooks.
Nathaniel von Einsiedel,
principal urban planner,
CONCEP Inc.