San Roque Dam strong vs earthquake, Phivolcs assures

An official of the Philippine Institute of Volcanology and Seismology (Phivolcs) on Wednesday allayed fears that the San Roque Dam in northern Luzon is vulnerable to earthquakes, stressing that the infrastructure is located far away from an active fault line. During the resumption of the Senate hearing on the effects of cyclones “Ondoy" (Ketsana) and “Pepeng" (Parma), Phivolcs director Renato Solidum Jr. said the dam is, in fact, seven kilometers from the fault line known as the San Manuel segment. "Yes, your honor, the San Manuel segment and the San Roque dam structure are seven kilometers apart, so the danger from rupture hazard is not there…," Solidum told Senator Loren Legarda, chairperson of the climate change committee, when the director was asked about the possibility that any movement of the fault line will affect the dam. Text messages saying that the dam was collapsing sparked fears among residents of several towns in Pangasinan after floods aggravated by the release of excess water from the San Roque Dam hit the province at the height of typhoon Pepeng two weeks ago. Local officials of Pangasinan have also earlier voiced similar fears and sought to halt the operations of the San Roque Multipurpose Project (SRMP). The National Power Corporation had replied that decommissioning the dam would deprive the country of its huge benefits. [See: Napocor rejects calls to shut down San Roque Dam] The controversy over the proper management of the dam's water releases has resulted in finger-pointing that might even end up in lawsuits against National Power Corp. (Napocor) officials by Pangasinan officials. Taken into consideration In allaying fears of the dam's collapse, Solidum explained that studies were made before the San Roque Dam was constructed, and that the location of the San Manuel fault line was taken into consideration in the reservoir’s design. Danger of ground rupture is only possible if the dam sits on top of the fault line, Solidum said, adding that ground-shaking caused by an earthquake can easily be mitigated by proper engineering. Located in the towns of San Manuel and San Nicolas, Pangasinan and Itogon in Benguet, the SRMP provides year-round irrigation for 70,800 hectares of farmland downstream largely in Pangasinan, but including parts of Nueva Ecija and Tarlac. It functions as a flood control structure as well, trapping sediment caused by erosion of small-scale mining upstream. Also during the hearing, Napocor vice president for engineering Danilo Sedilla said that the dam was designed taking into consideration the factors Solidum had mentioned. "During the call for bid for the dam, the Napocor issued a feasibility study…the engineering geology, which was made in March 1979, was part of the information given to the proponent for the San Roque Project… The information on these faults were already incorporated," Sedilla said. 1990 earthquake He further said that based on the information available to them, the dam can withstand a maximum of magnitude-7.8 earthquake. On the other hand, Solidum said the strongest earthquake experienced near San Roque Dam was magnitude-7.2 when the Digdig fault line in Nueva Ecija moved in 1990. He said the San Manuel fault line cannot create such magnitude of earthquake because it is shorter compared to the Digdig fault line. “Yung estimate na magnitude 7.2 earthquake ay batay sa haba ng fault line (based on the length of the fault line). The design of San Roque dam is over than the expected ground-shaking that might be caused by the movement of the San Miguel fault line," Solidum said. The San Roque Dam is the biggest of the three dams on the Agno River, and is designed to produce electricity, supply water and control floods. - GMANews.TV