MANILA – The former water-starved Angat Dam has increased its spilling operation in the aftermath of Typhoon Ulysses (international name Vamco) to better balance inflow and outflow of water and ensure the facility’s structural integrity.
The dam opened an additional gate on Friday so it can release more water, according to Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) hydrologist Edgar dela Cruz.
“Since (the) volume of water flowing into Angat is big due to ‘Ulysses,’ this dam had to increase release of its water,” he said.
He noted doing so aims to prevent Angat’s water from rising to a level that will already endanger the dam.
The spilling is moderate only to possibly prevent flooding risk in Angat’s downstream communities, he continued.
Angat Dam supplies water for irrigation, power generation, and Metro Manila’s needs.
Rain from successive onslaught of “Ulysses” and other tropical cyclones since October 2020 helped Angat recover from weeks of water shortage.
PAGASA said as of 2 a.m. Friday, two gates of Angat Dam were open at a total height of 1.00 meter to accommodate spilling operation.
Increased spilling operation was already in progress before noon Friday with three Angat gates open at a total height of 2.00 meters so the dam can release more water, said dela Cruz.
“That already slightly lowered Angat Dam’s water level,” he said.
From 214.21 meters at 10 a.m. on Friday, he said Angat’s water level dipped to 214. 20 meters an hour later when the outflow or water flowing from this dam reached 404 cubic meters per second (cms).
Such outflow is already more than Angat’s 11 a.m. water inflow of 357 cms on Friday, he noted.
“Inflow or entry of water into Angat is still big so increased spilling operation there continues,” he said.
He expects Angat’s water level to increasingly dip amidst such operation.
For the sub-basin where Angat Dam is, PAGASA forecast light rain during the 24-hour period ending 9 a.m. Saturday (Nov. 14).
Dela Cruz noted such forecast indicates a possible lesser flow of water into Angat Dam.
“Angat may already terminate its spilling operation this weekend if there’ll be no rain in the dam’s sub-basin,” he said.
“Ulysses” rain raised Angat Dam’s water level to beyond the 210.00 meters normal high-water elevation of the facility so spilling operations there commenced on Nov. 12, said dela Cruz.
He said “Ulysses” already moved away from the country but runoff from the typhoon’s rain continues to flow into Angat.
He said that is because Angat sub-basin cannot fully absorb the rains brought by “Ulysses” as the soil there is already saturated.
He said that Super Typhoon Rolly (Goni) this month already drenched and saturated the soil in the sub-basin.