Water-starved San Roque Dam may not fully benefit from the onset of rain-bearing La Niña phenomenon and the northeast monsoon or “amihan” which state forecasters expect to prevail later this month.

San Roque is located in Luzon’s west-lying Pangasinan province while La Niña and amihan generally affect eastern areas of the country, noted Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) hydrologist Richard Orendain.

“Unless there’ll be times when La Niña and amihan surge enough to bring much rain over San Roque so water level there can rise significantly, this dam will hardly benefit from both,” he said.

PAGASA reported San Roque’s 6 a.m. water elevation on Thursday at 240.48 meters only – 33.54 meters below the 274.02 meter-high rule curve elevation of the dam.

Rule curve indicates the level at which San Roque’s water must be for it to ably supply water for irrigation and power generation.

The water elevation on Thursday was also 39.52 meters below San Roque Dam’s spilling or normal high water level of 280 meters, PAGASA data showed.

This month, PAGASA announced the onset of the La Niña phenomenon.

La Niña is associated with above-normal rainfall in the country, noted PAGASA.

“Based on the latest forecast, weak to moderate La Niña is likely to persist until the first quarter of 2021,” the weather bureau said.

PAGASA also said transition from the southwest monsoon or “habagat” prevailing at present to amihan is underway.

Orendain expects San Roque to continue struggling for water throughout October 2020.

San Roque’s end-October water level will likely be around 235 meters only – still below both rule curve and normal high level of this facility, he noted.

“Water level in San Roque at present is already too low so this dam needs a lot of water to recover,” he said.

Even if La Niña and amihan rain fills up Binga Dam in Luzon’s Benguet province, he said water that this facility will release would not be enough to significantly raise San Roque’s water level.

Ambuklao Dam also in Benguet releases water to Binga Dam which, in turn, drains water to San Roque.

The three facilities comprise the series of dams the government built to support irrigation and power generation in the surrounding areas.(pna.gov.ph)

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