CITY OF SAN FERNANDO -- Experts have long been warning people of the dangers of living inside the FVR Megadike structure, particularly along the channels were lahar (mud) traversed.
Some 26 years since the eruption of Mt. Pinatubo, the Philippine Institute of Volcanology and Seismology (Phivolcs) is still issuing the same warning.
Jesse Umbal, a geologist and a former member of the Phivolcs Lahar Study Group, said that with the gradual depletion of source materials, volcanic debris still embedded at the foothills of the volcano, the frequency of lahar flows would diminish in the future.
"But the potential occurrence of lethal lahar flows still remains, particularly in the event of extreme rainfall," Umbal said.
In his study, Umbal identified two major Central Luzon river channels still active as lahar-draining routes -- the Pasig-Potrero River in Pampanga and the Marcella-Santo Tomas river channel in Zambales.
Of the two river channels, lahar flows in the Pasig-Potrero is more active, passing near eight towns including densely populated San Fernando, the capital city of Pampanga.
In the past, flows along the river almost totally buried the entire town of Bacolor, of the town's 21 barangays, only three were spared.
With the construction of the 1.4-billion megadike, lahar had been contained within the dike area.
The megadike was designed to ring some 100 kilometers of residential and agricultural lands near the Pasig-Potrero River in Porac, Angeles City, San Fernando, Santa Rita, Bacolor and Guagua and convert them into a huge lahar catch basin.
The dike is intended to save 10 Pampanga towns from volcanic sediments flowing from the Pasig-Potrero.
Even today, the Department of Public Works and Highways (DPWH) is doing additional reinforcing and slope protection works near the dikes portion in Santa Rita and Bacolor as well as near the dikes tail end in Guagua town.
But the taildike sections in Bacolor and Santo Tomas towns have always been areas of concern during heavy rains.
People have begun rebuilding homes inside the dike area in the past two decades, some even dangerously near hazard zones.
Last year, Phivolcs chief Renato Solidum warned that unusual rains from super typhoons may bring in flood water from large lahar deposits to active river channels.
Solidum suggested that the FVR megadike in Pampanga should be maintained and dredged continuously to prevent flooding and protect the residents in low-lying areas in the province.
"We have to make sure that these are strong enough to prevent erosion," he said. He added that the DPWH should monitor the dikes regularly especially during heavy rains.
Solidum earlier revealed that heavy rains that will be brought about by an Ondoy-like typhoon may trigger lahar flows and flooding in Pampanga.
In 2008, a study conducted by Phivolcs in Pampanga revealed that continuous rains may repeat massive flooding like the monsoon rains in 1972 that submerged many areas in Central Luzon.
An estimated 4,000 families reside in several Pampanga towns located inside the megadike, which was built during the time of President Fidel Valdez Ramos after lahar remobilized by rain overflowed from the Pasig-Potrero River on October 1, 1995, burying Bacolor town.
He said that over the past few years, no strong typhoons hit Central Luzon and Pampanga that may have triggered massive flooding and affect residents inside the megadike and other low-lying areas.