(UPDATE) SAN MANUEL, Pangasinan — The San Roque hydroelectric power plant here shifted to a "must-run" mode to lower the water level in its reservoir in anticipation of rains dumped by Typhoon Pepito.
This means that the power plant, which is a "peaking plant," will generate electricity 24 hours a day and release more water that it uses to turn its turbines, said Maria Teresa Serra, head of the National Power Corp.'s Flood Forecasting and Warning System Division (NPC-FFWSD).
As a peaking plant, the power plant, which has a maximum capacity of 435 megawatts (mw) of electricity, only operates during the peak hours from 9 a.m. to 3 p.m. and from 6 p.m. to 8 p.m. every day.
Serra said that by putting it in a must-run status in its peak capacity, it releases water at 270 cubic meters per second (cms).
As of 8 a.m. on Sunday, Nov. 17, the total water released from the dam is 618.48 cms after the dam's two spillway gates were opened at 1.5 meters high each to release 348.48 cms of water.
A cubic meter of water is 1,000 liters or about five drums of water.
Water released by the San Roque Dam flows downstream of the Agno River, traversing 24 towns and San Carlos City before exiting to the Lingayen Gulf.
Gov. Ramon Guico III had ordered preemptive evacuation of residents living along the river and those near the shorelines because the expected storm surges that may be caused by Typhoon Pepito.
In its advisory, the state weather agency said the heavy to intense (100 to 200 mm) rainfall was expected on Sunday in the provinces of Pangasinan, Catanduanes, Isabela, Nueva Ecija, Benguet, Ifugao, La Union, Bulacan, and Rizal.
Agno River's headwaters are at the slopes of the Mount Data, a mountain in the Cordilleras spanning the provinces of Benguet and Mountain Province.
The San Roque Dam is one of the three dams built in the Agno River, the other two being the Ambuklao Dam in Bokod, Benguet and the Binga Dam in Itogon, Benguet.
As cascading dams, water released by the Ambuklao flows to Binga, while the water spilled from Binga is caught by the San Roque Dam.
At 8 a.m. on Sunday, the water level at Ambuklao Dam was 750.42 meters above sea level (masl), just 1.58 meters below its normal high-water level of 752 masl. It has four gates open at 0.5 meter each, spilling water at the rate of 327.53 cms.
Binga Dam's water elevation has reached 572.29 masl, only 2.71 meters from its normal high-water level of 575 masl. It also has four spillway gates open at 0.5 meter each, discharging water at the rate of 260.66 cms.
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