'Closely monitor parts of Pampanga megadike'

ANGELES CITY , Philippines  – The flow of the upper reaches of the Pasig-Potrero River whose lahar buried almost the entire Pampanga town of Bacolor after Mt. Pinatubo’s eruption in 1991, has diverted toward this city and needs to be closely monitored amid the threat of typhoon “Santi.”

In an interview with The STAR, Philippine Institute of Volcanology and Seismology (Phivolcs) director Rene Solidum yesterday urged government engineers to monitor structures, especially old ones, which were constructed along former lahar channels emanating from Mt. Pinatubo.

Solidum cited studies showing that the upper reaches of the lahar-laden Pasig-Potrero River now tends to flow toward this city and that severe rains could lead to an overflow of the existing anti-lahar megadike a few kilometers from this city’s downtown and posh subdivisions.

In 1996, the government constructed a U-shaped megadike along the Pasig-Potrero River to contain the flow of lahar which had buried most of Bacolor town by then.

The dike prevented lahar from spreading to other threatened parts of Pampanga, including the cities of Angeles and San Fernando.

While volcanic debris on the upper slopes of Mt. Pinatubo have almost been depleted, volcanic deposits in river channels could still be remobilized, particularly during the rainy season.

In case of “extreme rains,” Solidum said millions of cubic meters of combined water and volcanic materials could still flow through the Pasig-Potrero.

Because of this, there is a need for continuous dredging of the river’s channel to prevent it from overflowing or damaging the megadike.

He said quarrying of lahar materials could be done in the Pasig-Potrero to preserve the channel’s depth, but stressed the need for government engineers to manage the quarrying.

Solidum, however, said a possible overflow at the section of the megadike toward Angeles City is expected to be of “minor” magnitude. 

Meanwhile, Barangay Cuayan chairman Arturo Candelaria has sounded the alarm over breached portions of the Taug dike along the Abacan River in this city.

The Abacan River also used to be a lahar channel until a “secondary explosion” on Pinatubo’s slopes in 1993 triggered changes that blocked lahar deposits from flowing through it and the Sacobia River in Tarlac, diverting lahar flows to the Pasig-Potrero.

Solidum said though that floodwaters, not lahar flows, could threaten this city in case the dike is breached.