Can Ambuklao dam contain supertyphoon rains?

BAGUIO City—A Benguet mayor has urged authorities reviewing flood control protocols to study how much rainwater can be contained by some of the country’s oldest dams, including the newly recommissioned Ambuklao Dam in Bokod town.

Bokod Mayor Mauricio Mackay said old dams, like the 60-year-old Ambuklao, contain decades’ worth of silt, thus reducing storage space for rainwater.

Instead of retaining rainwater for longer periods, old dams may be forced to discharge the water immediately, Mackay said. This adds pressure on low-lying dams that capture runoff water released from the dams in the mountains, he said.

Agencies that oversee the dam have varying information on how much silt it has actually accumulated, although experts agree that silt appears to have displaced a third of the reservoir’s storage capacity.

Silt is sedimentation composed of soil and rock, which is discharged into the river systems by human activity or by degraded mountain walls.

Operators of Ambuklao believe that expanding the watershed is a better way to regulate the flow of dam water, instead of dredging the dam.

According to data from the Department of Environment and Natural Resources (DENR), the Cordillera serves as the watershed and main source of river water to power five hydroelectric facilities, including Ambuklao, which will resume operations on October 26.

The Agno River, which powers up Ambuklao and neighboring 100-MW Binga Dam in Itogon town, covers 128,752.25 hectares. Its water drains into San Manuel town in Pangasinan, where the San Roque multipurpose dam is located.

The Magat River, which spans 232,445.57 hectares, feeds into the Magat Dam before it drains into Roxas town in Isabela.

“I am raising this matter with the National Power Corp. (Napocor) as an input [to studies of flood control systems that are being undertaken] so we have a better way of dealing with stronger typhoons,” Mackay said.

In Bulacan, the Power Sector Assets and Liability Management (PSALM)  released P33 million so that Napocor can undertake a six-month study to determine the capacity of the 43-year-old Angat Dam to cope with climate change, said Alfredo German, general manager of the Napocor-controlled Angat River Hydroelectric Power Plant (Arhepp).

German said that the government will soon sign a memorandum of agreement with New Zealand environmental engineering consulting firm Tonkin and Taylor, and Engineering Development Corp. of the Philippines (Edcop).

Bulacan Governor Wilhelmino Sy-Alvarado had demanded a study, arguing that Angat Dam “is already 43 years old [and] the life span of a dam is only 50 years.”

The 75-MW Ambuklao hydroelectric power plant was commissioned in 1950 while the Binga plant was commissioned in 1959.

Ambuklao was idle from 1999 to 2011, until it was reconditioned and upgraded to generate 105 MW of electricity by SN Aboitiz Power Corp. (SNAP).

SNAP, a joint venture between SN Power of Norway and Davao-based Aboitiz Power, acquired the power plant along with Binga, during a 2007 government auction.

SNAP also bought Magat Dam, which straddles Ifugao and Isabela.

Michael Hosillos, SNAP vice president for communications, said the company’s upgrade took into account “mountains and mountains of silt that had built up for the past 60 years,” but engineers concluded that dredging the silt would not be feasible.

Previous Ambuklao and Binga leaseholders tried but failed to remove the silt.

Hosillos said: “We are studying how the silt would affect our operations, but we have since installed equipment that would make power generation efficient.”

“We commissioned foreign experts to study Ambuklao, Binga and Magat dams and they believe these facilities could last a hundred years,” he said.

Instead of dredging, the company tunneled down the silt to improve the facility’s power-generating capacity, Hosillos said.

“There is also the environmental issue of disposing the silt because where in the mountains can we unload 60 years’ worth of silt? We prefer building forests and coordinating with the people so we can reduce river pollution,” he said.—With a report from Carmela Reyes-Estrope, Inquirer Central Luzon