Why Tuguegarao floods

Each time floodwaters submerge Tuguegarao City, public anger is quickly directed at one structure: the Magat Dam. Its visible spillways, dramatic water releases, and sheer physical presence make it an easy symbol of blame. Yet a closer examination of scientific research, watershed conditions, and hydrological data shows that flooding in the city is driven by far deeper and more systemic causes. Tuguegarao lies entirely within the Cagayan River Basin, the largest river system in the Philippines, draining more than 27,000 square kilometers across multiple provinces. What happens in the mountains of Nueva Vizcaya, Isabela, Kalinga, and the upper Cagayan Valley inevitably converges in the city’s low-lying areas.

Comprehensive studies conducted by the Japan International Cooperation Agency show that the lower stretch of the Cagayan River, including the section that passes Tuguegarao, has a very limited discharge capacity of only about 2,000 cubic meters per second. The river’s slope in this area is extremely gentle, slowing water movement and causing floodwaters to accumulate easily during intense rainfall. Even moderate flood events can exceed the river’s carrying capacity, making flooding not an abnormal occurrence but a geographic certainty under heavy weather conditions. This natural limitation alone already puts Tuguegarao in a position of permanent flood vulnerability.

While dam operations dominate public discussion, scientific findings point to the condition of the watershed as a major driver of severe flooding. JICA research shows that forest cover in critical upstream areas has steadily declined over the decades. With fewer trees to absorb rainfall and stabilize slopes, runoff accelerates, erosion intensifies, and massive volumes of sediment are carried into the river system. This sediment raises the riverbed, reduces channel depth, clogs tributaries, and weakens the ability of the river to safely convey floodwaters. During major flood events, residents and disaster responders have repeatedly observed floating logs, uprooted trees, and heavy debris rushing downstream. These are not signs of a healthy watershed but indicators of sustained tree cutting in upland areas, including illegal logging.

Recovered timber after floods has been documented not only along the lower Cagayan River but also in areas near the Magat reservoir itself. Each log recovered is evidence of continued forest loss upstream, where tree cover once served as a natural flood control system. As forests disappear, rainwater moves faster, soil collapses more easily, sediments accumulate more rapidly, and river channels become progressively shallower and more destructive with every passing year.

The Magat Dam, often blamed during flood events, was designed primarily for hydropower generation and irrigation rather than full-scale flood control. Over the years, it has been burdened with expectations far beyond its original engineering purpose. During recent floods, Magat Dam management clarified that only a small portion of the water level rise in Tuguegarao could be attributed directly to dam releases. Dam officials, including Carlo Ablan, Division Manager A of the National Irrigation Administration–Magat River Integrated Irrigation System, said only about half a meter to one meter of the total floodwater height in Tuguegarao was due to water discharged from the dam, while the bulk of the volume came from simultaneous heavy rainfall across multiple tributaries feeding the Cagayan River.

JICA warned years earlier that even a well-operated dam cannot counteract the combined effects of deforestation, slope instability, and basin-wide runoff. Sedimentation has also significantly reduced the dam’s effective storage capacity. After major earthquakes and sustained erosion upstream, more than half of the dam’s dead storage was filled with sediment within just a few decades of operation. This has steadily reduced the dam’s ability to temporarily store floodwaters during extreme weather events and further limited its flood mitigation role.

Flooding in Tuguegarao, therefore, is not solely the result of dam operations. It is the outcome of decades of environmental degradation across the river basin. Tree cutting strips slopes of their natural anchors. When rain falls, soil collapses into rivers, accelerating sediment buildup and narrowing channels. Each year that illegal logging continues, the river system becomes shallower and more dangerous. Yet enforcement against illegal logging in upland areas remains inconsistent. Timber continues to be recovered only after floods, when the damage has already been done. The upstream destruction remains largely unseen, but its consequences are repeatedly felt downstream.

Tuguegarao sits at the natural convergence point of massive upstream runoff, reduced forest cover, heavy sediment accumulation, limited river discharge capacity, intensified rainfall patterns, and expanding urban development along natural floodplains. This combination makes the city structurally vulnerable regardless of how dams are operated. Floodwaters arriving in Tuguegarao are no longer controlled by a single source but by the combined force of the basin’s rivers and tributaries.

Experts have long maintained that flood control cannot succeed without restoring the watershed. JICA has recommended large-scale reforestation of upland slopes, construction of sediment-control structures in erosion-prone tributaries, strengthened riverbank protection, and coordinated basin-wide flood forecasting systems. Many of these proposals remain only partially implemented decades after they were first raised.

Flooding in Tuguegarao is not the product of one structure. It is the consequence of long-term environmental neglect across an entire river system. Until illegal logging is decisively addressed, forests restored, sediment managed, and river systems rehabilitated, flooding will remain a recurring threat.