Philvolcs warns Bulacan execs on Angat Dam disaster scenario

By George Trillo

MALOLOS CITY– Prepare for the worst.

This warning was aired by Dr. Renato Solidum of the Philippine Institute of Volcanology (Phivolcs) to Bulacan officials during a recent committee hearing of the Sangguniang Panglalawigan on the status of the Angat Dam in Norzagaray town.

This developed as officials of the National Power Corp. and the Metropolitan Waterworks and Sewerage System said the dam remains stable, saying it has no crack, but Vice Gov. Wilhelmino Alvarado wasn’t convinced, saying he found larger “cracks.”

“I suggest that you prepare for the worst scenario on your disaster management and coordinate with the managers of Angat Dam,” Solidum told SP members as he confirmed the main dike of the dam is sitting or near the vicinity of the West Valley fault which is part of the Marikina fault line system.

He said in the last 1,000 years, the Marikina fault line system recorded four strong earthquakes close to magnitude 7 on the Richter scale.

“The interval of the major movement of the West Valley fault is between 200 and 400 years,” he said noting that the lower interval of 200 years had passed.

Unable to predict the next movement of the West Valley fault, he said, “probability wise, parang malapit na yung susunod na movement.”

However, Solidum hinted that the West Valley Fault is currently ‘locked’ saying they have not observed a major movement in the past years.

According to Solidum, the magnitude of an earthquake is dependent on the length of the fault system, and cited that the West Valley fault is capable of earthquake with at least seven in magnitude.

Experts confirmed in a 2002 study that the West Valley fault stretched from Taal Lake to Angat River in Bulacan.

The MWSS said in a document used to justify the construction and operation of the proposed Laiban Dam project cited Report No. 1 of Dr. Kaare Hoeg of the Norwegian Technical Institute on Nov. 29, 2002 that said, “the new information about the Marikina fault and the uncertainties related to the future earthquake loads, and due to lack of performance monitoring to evaluate the present conditions of the structures, the level of risk involved is unacceptable.”

For their part, engineers Romualdo Beltran of Napocor and Jose Dorado of the MWSS said the Angat Dam remains structurally stable.

Beltran said the dam is not concrete, but is actually a rock-fill embankment that will not be easily damaged.

He said that when built in the mid-60s, the dikes of the Angat Dam passed the Japanese standards.

“Kung sakaling masisira ng lindol, hindi basta magigiba yung dike ng dam, instead, its rock, soil and sand composition will only be compacted below,” Beltran said.

The same was echoed by Dorado who said that Angat Dam is safe under normal conditions.
He and Beltran reiterated that the dam dikes have no crack which appeared to satisfy some members of the Sangguniang Panglalawigan who left long before the hearing was over.

The move of some of the members of the Sangguniang Panglalawigan of Bulacan prevented them from hearing the warnings of Solidum who said that the province must now prepare for the potential impacts of earthquake on the dam.

The same was echoed by Alvarado who said he is not convinced yet with the denial of Beltran and Dorado on the presence of crack on the dam.

Alvarado insisted that Dumagat tribesmen living within the Angat Watershed area have repeatedly informed him about the crack.

One of them is Baldomero Diesta who even attended and testified during the hearing.
Alvarado, however, said that he is not trying to paint a dooms-day scenario, but is only calling the attenion of everybody and echoing the document used by the MWSS which also stated that the Angat Dam is old and seepage has been observed since its completion in 1967.