Unearthing Lessons: Revisiting the Debris Flow Tragedy in New Bataan, Compostela Valley

The Philippines. Known for its breathtaking landscapes and rich natural resources. However, this enchanting beauty comes with a geological cost, as the country is prone to a myriad of geologic hazards. From volcanic eruptions and earthquakes to landslides and typhoon-induced flooding, the Philippines faces an array of challenges that stem from its complex tectonic setting, and for decades, The Philippines experience number of geologic hazards that not only damages and disrupts the economy but also exposes lives onto a great risk of danger from mass wasting.

Recalling from one of the devasting geologic hazards happened in the history of the Philippines, the Debris flow event last November 2012 in New Bataan, Compostela Valley, let's take a look on the research article made by Kelvin Rodolfo and his team titled: Super Typhoon Bopha and the Mayo River Debris-Flow Disaster, Mindanao, Philippines, December 2012.

A Category 5 Super Typhoon Pablo, international name, Bopha, hit the island of Mindanao and delivered roughly above 4.4M cu.m of rainfall throughout the area, causing around 1.04 Billion USD of damage in buildings, infrastructures, and local livelihood. The event that really damaged the municipality of New Bataan is the debris flow that was induced by the torrential rain that was occurred by the Typhoon Pablo. Fig 1.

Exploring the causes behind the debris flow incident requires a closer examination of factors such as geomorphology, statistical data on the torrential rainfall from the typhoon, and other geological aspects. To begin, let's delve into the geographical positioning of the municipality of New Bataan in Compostela Valley.

Andap in New Bataan is situated at the base of a mountain where the Mayo River collects water from its watershed. Studies have indicated that a significant portion of the slopes within the watershed exceeds a steepness of 35 degrees and is positioned at an elevation of approximately 2300 meters. Figure 2.0 illustrates that the municipality is influenced by the structural presence of the Mati Fault, leading to extensive fracturing and the accumulation of substantial rock debris along its course.

Now if you can see the contour lines from the Mayo bridge to Andap, it creates a convex upward shape conveying an alluvial fan representing history of sedimentation of past debris flows.

The figure below provides a statistical overview of the rainfall volume received by the area during the 12-hour period when the substantial debris flow occurred.

This shows that the river received around 120mm from 12 midnight of December 4, 2012 up to the start of the debris flow at 6:30 am. With rate of rain fall of 43mm/hr, it exceeded the debris-flow initiation thresholds at past debris flow event in Mt. Pinatubo. These factors are the main drivers of hosting a massive natural disaster that the municipality awaits.

Now let's take a short video of the damages taken by the New Bataan after the debris flow event.

You can also see here in Figure 4. the impact made of the Mayo River Debris flow to barangay Andap, New Bataan.

The whole country was devastated during that time and the disaster accounted around 566 lifeless bodies found throughout the area. Schools were destroyed, Hospitals, buildings and livelihood were wasted leaving nothing for the locals after the storm.

Preventive Solution

In the wake of the devastating debris flow event triggered by Typhoon Pablo(Bopha) in 2012, a critical lesson emerged in the importance of proactive measures to safeguard vulnerable communities. Recognizing the urgent need for preventive solutions. The National Government already finished the nationwide hazard mapping led by the Philippine Institute of Volcanology and Seismology called the Project NOAH. This initiative will help the local government and the technical people in the DPWH and LGU's to prepare some mitigation measures and set up early warning system in order to safeguard the infrastructures and lives of the community. Additionally, there are new technologies that are emerging here in the Philippines like the usage of Debris Flow Barrier, and an Early Warning Device called HelloMac from Maccaferri. These specialized barriers act as formidable guardians, strategically positioned to intercept and mitigate the destructive force of debris flows. By leveraging engineering expertise and technology, these barriers serve as a first line of defense, redirecting debris away from settlements and infrastructure.

The painful experience of the 2012 disaster has propelled companies like Maccaferri to invest in sharing technical knowledge about the protective capacity of these barriers as a vital step towards fortifying people against the unpredictable forces of nature. Another technological solution for early warning systems that we can integrate is the HelloMac. This system can be retrofitted onto either a rockfall barrier or debris flow barrier, providing timely notifications to local government units (LGUs). This enables them to take prompt and suitable actions, including the installation of roadblocks and the issuance of evacuation announcements.

As we reflect on the past, future deployment of these kinds of technology like the debris flow barriers stands as a testament to our collective determination to learn from tragedy and build a safer, more resilient future. Now, as leaders, engineers, and scientists, let's introspect and consider what additional measures we can take to shield our communities and our nation from the impact of such catastrophic events.