CABANATUAN CITY—Amid fears of the “Big One” earthquake striking anytime, the new administrator of the National Irrigation Administration has ordered the agency’s engineers to inspect Pantabangan Dam and other dams in the country to ensure their structural integrity.
NIA Administrator Ricardo Visaya told reporters following a visit at the Upper Pampanga River Integrated Irrigation Systems office here that his men had just concluded training on determining the quake preparedness of dams.
They will soon undertake an engineering assessment of all dams, including the Pantabangan Dam, he added.
Visaya witnessed the installing of new NIA-UPRIIS Division III manager Engineer Jose Ariel G. Domingo after the compulsory retirement of Engineer Joselito Mangunay this May.
“With talks of this ‘Big One,’ we will consider the structural integrities of our dams to ensure the people are safe,” he said.
The Philippine Institute of Volcanology and Seismology has sounded the alarm for the “Big One” that could level Metro Manila, which is bisected by the West Valley Fault.
Phivolcs said that while there is no instrument to predict the occurrence of earthquakes, a tremor in Metro Manila is expected because of the possible movement of the West Valley Fault.
Pantabangan Dam is the country’s largest dam that irrigates over 100,000 hectares of farmlands in Central Luzon.
In March 2011, then-NIA administrator Antonio Nangel claimed the earthen dam, the first and single largest infrastructure ever accomplished by the government, can survive an Intensity 10 earthquake.
Nangel said Pantabangan Dam was so designed and constructed to withstand powerful earthquakes. “It was sturdily built. And since it is an earth dam, it has flexibility, so we see no problem. In fact, it can survive even an Intensity 10 earthquake,” he said.
Since 2011, some quarters have raised fears some of the country’s dams might not be able to survive powerful tremors akin to, if not more powerful than, the 9.2 temblor that hit Japan and killed thousands.
Nangel was once manager of UPRIIS, the country’s largest national irrigation system, which operates Pantabangan Dam.
The dam was built in 1971 by an all-Filipino consortium of engineers and completed in August 1974, 17 months ahead of schedule at a cost of P800 million at that time, including a $34-million loan from the World Bank. The structure was located at the center of the Carranglan, Pantabangan, and Pampanga Rivers.
The dam consists of two zoned earth-filled dams – the main dam and the Aya Dam. Its 8,420-hectare reservoir area has a water storage capacity of 1.75 billion cubic meters for irrigation and power generation. Its watershed area covers 90,900 hectares.
The dam also provides flood control, water supply for domestic and industrial purposes, fish conservation, and tourism.
To illustrate its readiness to survive a powerful earthquake, Nangel said the dam withstood the July 16, 1990 killer quake that hit Baguio City, with no damage to its reservoir area and other structures.
“Even if there was a fault line in Digdig (in nearby Carranglan), there was never any ill effects on the operations of the Pantabangan Dam back then,” he said.
The 1990 tremor, listed at Intensity 7.7 in the open-ended Richter Scale, however, considerably affected the natural flow in the downstream portions of the Pantabangan Dam at the Digdig and Talavera rivers. It also reduced the service area of the Talavera River Irrigation System from 6,000 hectares to only 500 hectares.
The UPRIIS’ dam and reservoir division is maintaining the Pantabangan Dam’s structural soundness and safety as well as monitor and regulate the release of water from its reservoir.