LINGAYEN, Pangasinan—With bated breath, Pangasinenses waited for hourly updates on the water level at the San Roque Dam in San Manuel town as Typhoon Pedring dumped heavy rains in northern Luzon last week.
As Pedring headed for the West Philippine Sea on September 28, the dam’s water level rose from 264.88 meters above sea level (masl) the previous day to 275.96 masl.
No spillway gate was opened at that time. Dam officials issued statements assuring residents that the dam could still absorb more water, saying the water elevation was way below its spilling level of 280 masl.
Virgilio Garcia, hydrologist and dam operations manager of National Power Corp., said in a press briefing last month that the dam’s spillway gates would only be opened when four conditions were present—when the reservoir elevation has reached 280 masl, when there is typhoon in “typhoon marking area I (area around Luzon and Visayas),” when the inflow (water entering the reservoir) is 500 cubic meters per second (cms) or more, and when rainfall is 60 millimeters or more in a day.
But Governor Amado Espino Jr. did not want to take chances. With Typhoon “Quiel” heading toward northern Luzon at that time, he knew that more rains would fall over northern Luzon and the dam’s water elevation would increase rapidly.
Besides, the heavily silted Ambuklao and Binga dams upstream in Benguet had opened all their spillway gates. The water released by these dams is impounded by the San Roque Dam.
Power generation
Not wanting a repeat of the 2009 massive flooding in Pangasinan when dam operators released excess water at the rate of more than 5,000 cms, Espino called officials of San Roque Power Corp. (SRPC) to ask them to maximize its power generation.
“That way, there’s already an outflow,” Espino said. The dam can generate at most 406 megawatts (MW) with an outflow of 260 cms.
Before Pedring hit the country, SRPC was only producing 135 MW, with an outflow of 90 cms. Tommy Valdez, vice president for corporate social responsibility, said this was because the firm was only allowed to supply power to northern Luzon.
At full power generation, the company would be able to supply the Luzon grid, he said.
As more rains fell on September 28, the dam’s water elevation quickly rose to 277 masl. That night, Napocor announced that it was opening a gate at half meter at noon on September 29, with an outflow of 79 cms. On the day the spillway gate was opened, the dam’s water elevation was already a little more than 280 masl.
But Pangasinenses were not impressed. The outflow was too little, said former Pangasinan Representative Mark Cojuangco, who had been prodding Napocor officials to release as much as 500 cms as a preemptive measure.
Napocor officials did not budge, saying the dam could still absorb water up to 290 masl. This was the same argument they used in 2009 when they released water when the dam’s reservoir was already approaching the 290 masl mark.
More water spilled
On October 1, a few hours before Quiel ripped through northern Luzon provinces, Espino asked an SRPC official to maintain the dam’s water level at 280 masl. This meant increasing the volume of water being spilled while the Agno River could still absorb it.
As more rains were dumped on Saturday and Sunday, the dam’s water only reached 285 masl. Water continued to be spilled into the Agno River without breaking a dike and without causing massive flooding in the province.
When the skies cleared on Monday, only 51 villages in 20 towns and cities of the province experienced flooding but mostly because of storm surges and high tide.
Some eastern towns were flooded because of breached dikes along the Ambayoan and Dipalo rivers, which both flow from the Caraballo mountains.
But this figure pales in comparison with the devastation in the province in 2009 when rains dumped by Typhoon Pepeng and excess water released by the San Roque Dam submerged 38 towns and cities and ravaged some P4 billion worth of crops, fish, roads, bridges and dikes.
Aside from closely watching the dam’s water level and applying pressure on dam officials for a preemptive release of water, the province had adequately prepared for the floods, Espino said.
Espino said the provincial government’s preparation began last year by dismantling all fishing structures in rivers traversing the coastal areas.
“We wanted our rivers to flow freely and unimpeded,” he said. The clearing operation was followed by dredging the mouth of the Agno River at the Lingayen Gulf to increase its carrying capacity.
“These efforts helped in a way in mitigating flooding in the communities because floodwaters can now flow faster,” Espino said.