Wednesday , April 25, 2018

Communities within Mega Dike structure still at risk

CITY OF SAN FERNANDO -- Since the devastating eruption of Mt. Pintubo in 1991, communities within Bacolor's mega dike system are still at risk from possible lahar (mud flow) that may be brought by the irregular weather and strong typhoons from climate change.

Philippine Institute of Volcanology and Seismology (Phivolcs) chief Renato Solidum warned since 2016 that unusual rains from super typhoons may bring in flood water from large lahar deposits from the upstream area to Pinatubo's still active river drainage channels.

“The dikes have to be continuously maintained and the channels should be regularly dredged,” he said with emphasis on the upper section of the Pasig-Potrero River where a megadike was built, urging continuous monitoring.

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.

But despite the drawing up and use of lahar hazard maps and scenarios that present severe but reasonable predictions of areas that may be affected for planning purposes, areas within the dike systems in Bacolor and Porac town have seen to the steady increase of settlers along hazard areas.

In fact, in Bacolor town alone, commercial infrastructures like warehouses and several large constructions have been seen recently within the dike area.

Solidum said those who were allowed to build homes within the megadike are at risk in the event of continuous rains.

According to the U.S. Geological Survey Fact Sheet 114-97, the volume of Pinatubo's lahars staggers the mind. In the first few years following the cataclysmic 1991 eruption, they have deposited more than 0.7 cubic miles (3 cubic kilometers; equivalent to 300 million dump-truck loads) of debris on the lowlands surrounding the volcano, burying hundreds of square miles of land. During heavy rains, lahars at Pinatubo can transport and deposit tens of millions of cubic yards of mud in a single day.