As of yesterday, Jones Gacutan, officer-in-charge of the NIA’s flood forecasting division, said the water level at the dam’s reservoir was measured at 216.34 meters, the highest since 1978 when the Upper Pampanga River Integrated Irrigation Systems (UPRIIS), which operates the dam, was forced to open the spillway gate to release water.
Gacutan said they have sounded the alarm to low-lying areas that they would release water once the spillway level would reach the 221-meter mark.
He said the possibility of the dam being filled up to the brim would depend on rainfall in the coming days.
Edilberto Payawal, department manager of the NIA’s systems management division, attributed the high water level to the Casecnan Dam, which diverts water from the Taang and Casecnan rivers to the Pantabangan Dam through a 26-kilometer underground transbasin tunnel.
Because of the Casecnan Dam, Pantabangan Dam has a guaranteed inflow of 800 million cubic meters of water annually, allowing it to irrigate an additional 35,000 hectares on top of the 102,000 hectares.
The World Bank-funded Pantabangan Dam was constructed in 1975, 13 years after it was conceived. Aside from irrigation, it is also equipped with power-generating facilities with an installed capacity of 100 megawatts.
Engineer Antonio Nangel, UPRIIS operations manager, said the inflow rate of water to the dam was placed at 116 cubic meters per second when it was measured at 215.88 meters last Aug. 24.
Engineer Raffy Cardona, NIA supervising industrial relations development officer, told The STAR that the agency was forced to open the spillway gate in 1978 when supertyphoon "Kading" pounded Luzon and left a trail of destruction in southern Nueva Ecija and Bulacan.
Unlike Gacutan, Cardona, however, downplayed the dangers of the dam’s overflow, saying it would take at least three strong typhoons for its reservoir to fill up.
Cardona said the 107-meter high, zoned earth- and rock-filled dam, which has a catchment area of 853 square kilometers, has a gross storage capacity of three billion cubic meters of water.
He said the dam’s water level rose because the NIA suspended the delivery of water in the past weeks.
"It is still safe. There is no cause for alarm," he said, referring to low-lying areas that include the thickly populated Cabanatuan City.