PANGASINAN, Philippines — San Roque Dam is set to open two gates Wednesday morning, September 2, in a controlled release aimed at bringing down its rapidly rising reservoir level, putting communities along the Agno River on heightened watch as rains continue to affect Northern Luzon.
The San Roque Power Corporation announced that two gates of the massive reservoir in San Manuel, Pangasinan will be opened beginning at 8 a.m. Wednesday, releasing an estimated 300 cubic meters of water per second (cms).
The move comes after the dam’s reservoir climbed to 283.68 meters above sea level as of noon Tuesday, September 1, already several meters above its 280-meter mandatory spilling level.
Authorities described the discharge as a controlled and precautionary release, intended to prevent the reservoir from continuing to rise amid recent heavy rainfall and large volumes of water flowing into San Roque from upstream.
Communities Along Agno River Told to Stay Alert
The National Power Corporation advised communities downstream of the dam to prepare for changing river conditions once the release begins.
Among the municipalities specifically identified in the advisory are San Manuel, San Nicolas, Asingan, Tayug, Sta. Maria, Rosales, Sto. Tomas, Alcala, Bautista and Bayambang.
Residents near the Agno River have been urged to closely follow announcements from local disaster offices, the Pangasinan Provincial Disaster Risk Reduction and Management Office, NPC and San Roque Power Corporation.
The Pangasinan provincial government said disaster-response agencies are coordinating with local governments to ensure warnings can be issued quickly should river levels rise significantly.
Authorities have not announced that the planned 300-cms discharge will automatically result in widespread flooding. However, communities near riverbanks and already flood-prone areas are being advised to remain vigilant because dam releases are only one of several sources of water entering the Agno River system.
San Roque Reservoir Rose Rapidly in Recent Weeks
The situation is particularly significant because of how quickly the reservoir has filled.
On August 3, San Roque’s water elevation stood at about 226 meters above sea level. By August 15, following heavy rains associated with tropical cyclones and the southwest monsoon, it had jumped to 267.4 meters.
The reservoir continued climbing.
By 8 a.m. on August 31, PAGASA data placed San Roque at 279.85 meters, after gaining 4.76 meters in only 24 hours. By noon that day, provincial monitoring data showed the reservoir had already reached 280.52 meters.
At noon Monday, San Roque was receiving an estimated 947 cms of inflow, according to information released by the Pangasinan provincial government.
By noon Tuesday, the reservoir had climbed further to 283.68 meters, prompting the decision to open two gates Wednesday.
Water From Benguet Dams Also Feeding San Roque
The pressure on San Roque does not come from rainfall over Pangasinan alone.
San Roque sits downstream of the Ambuklao and Binga dams in Benguet, creating a connected reservoir system within the Agno River basin.
As of Monday morning, Ambuklao had eight gates open, while Binga had six gates releasing water. Water discharged from those reservoirs eventually flows toward San Roque. PAGASA had placed both the Agno River Basin and the Ambuklao-Binga-San Roque sub-basin under flood watch amid continuing rains.
That upstream flow has become a major factor in determining how quickly San Roque must release water downstream.
Habagat Continues to Bring Rain to Pangasinan
Weather conditions are adding another layer of concern.
PAGASA said Tuesday that the southwest monsoon, or habagat, continues to affect Luzon, with light to moderate rains expected over Pangasinan and several other parts of Northern Luzon.
Tropical Storm Pilandok also intensified Tuesday while remaining far east of Extreme Northern Luzon. PAGASA said the cyclone was unlikely to make landfall, but the southwest monsoon remained responsible for potentially significant rainfall across parts of the country.
That means dam operators are not simply dealing with the water already inside San Roque. They must also maintain enough reservoir space to accommodate additional inflows should heavy rainfall continue over the Agno River watershed.
Why Officials Are Releasing Water Before It Climbs Higher
Controlled releases are designed to gradually create additional storage capacity instead of allowing reservoir levels to rise unchecked during prolonged rainfall.
San Roque had already begun releasing water through its low-level outlet on August 26, when the reservoir stood at 275.45 meters. That earlier pre-release was set at about 150 cms.
Officials at the time said the strategy was intended to manage the reservoir before conditions forced larger releases.
The issue carries particular sensitivity in Pangasinan because of the devastating flooding associated with Typhoon Pepeng in 2009.
During that disaster, San Roque’s reservoir approached its 290-meter crest and large areas of Pangasinan were inundated. The episode later resulted in legal disputes over allegations surrounding dam operations and the timing of water releases.
Since then, dam operators have increasingly relied on precautionary releases when severe weather and rising reservoirs make additional storage space necessary.
The Bigger Question Is What Happens After Wednesday’s Release
For now, Wednesday’s 300-cms discharge is a controlled operation, not an announcement that catastrophic flooding is imminent.
But the situation remains fluid.
How much water ultimately moves through the Agno River will depend not only on San Roque’s releases, but also on rainfall, upstream discharges from Ambuklao and Binga, tributary flows and existing water levels downstream.
The Agno River itself receives water from several other waterways, including the Ambayaoan, Banila and Dipalo-Viray rivers, while the Tarlac River joins the system around Bayambang.
That is why authorities are emphasizing monitoring rather than panic.
As the two San Roque gates open Wednesday morning, the immediate goal is clear: lower the reservoir and create room for whatever water may still be coming from the mountains.
The bigger question for Pangasinan is whether the weather—and the massive Agno River system downstream—will give operators enough room to do it safely.
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