MANILA, Philippines — Authorities have placed La Mesa Dam in Quezon City under Alert Level 3 as relentless Southwest Monsoon or Habagat rains continue to push up water levels and raise the risk of flooding in low-lying communities.
The Quezon City Disaster Risk Reduction and Management Council reported that La Mesa Dam’s water level reached 79.71 meters at around 5 a.m. on Tuesday, August 18, up from 79.69 meters recorded the previous afternoon.
The latest figure remains below the dam’s 80.15-meter spilling level, meaning La Mesa Dam had not yet breached its overflow elevation at the time of the report. However, the water level had already crossed the 79.50-meter critical threshold associated with Alert Level 3.
Flooding risk shifts to communities along Tullahan River
The rising water level is particularly concerning for communities downstream of La Mesa Dam.
Quezon City officials warned that excess water from the reservoir could affect low-lying portions along the Tullahan River, including Fairview, Forest Hills Subdivision, Quirino Highway and San Bartolome.
Earlier on Monday, the Quezon City government also identified several other communities that could be vulnerable if water levels in the Quirino-Tullahan River increase, including Bagbag, Nagkaisang Nayon, Sta. Lucia, North Fairview, Lagro, Commonwealth, Novaliches Proper, Gulod, Capri, Sta. Monica and Talipapa.
Authorities have urged residents in flood-prone areas to remain vigilant, monitor official advisories and prepare for possible evacuation should water levels rise further.
Metro Manila was battered by intense rainfall
The La Mesa Dam alert comes after an intense bout of rainfall across Metro Manila on Monday.
PAGASA data cited by GMA News showed that 201.7 millimeters of rain fell in Metro Manila in just five hours on August 17, highlighting the exceptional amount of water dumped over the capital during the Habagat episode.
The continuing monsoon rains have also caused widespread flooding and prompted authorities to closely monitor dams and waterways across Luzon.
PAGASA’s August 18 dam monitoring showed La Mesa Dam at 79.70 meters at 8 a.m., with the reservoir still 0.45 meter below its 80.15-meter normal high/spilling elevation.
Other Metro Manila waterways also monitored
While La Mesa Dam remained at Alert Level 3, water levels in several major Quezon City waterways were also being watched closely.
As of 5 a.m. Tuesday, the Marikina River stood at 14.98 meters, the Quirino-Tullahan River at 38.44 meters, and the San Juan River at 11.97 meters. No alert level was reported for those three waterways in the same update.
The situation represented an improvement from Monday, when several waterways had reached elevated alert levels amid the heavy rains. On Monday afternoon, for example, La Mesa Dam was recorded at 79.69 meters, while the San Juan River reached Alert Level 3.
Habagat expected to continue affecting Luzon
PAGASA said the Southwest Monsoon or Habagat would continue affecting western portions of Luzon and the Visayas.
For Tuesday, monsoon rains were expected over areas including Benguet, La Union, Pangasinan, Zambales, Bataan, Cavite and Occidental Mindoro, while occasional rains were forecast over Metro Manila and several neighboring provinces.
PAGASA also issued heavy rainfall warnings over parts of Luzon Tuesday morning, including a red rainfall warning for Batangas, Zambales and Bataan, an orange warning over Cavite and other areas, and a yellow warning covering Metro Manila and several nearby provinces.
Why La Mesa Dam’s level matters
La Mesa Dam is particularly important to flood monitoring in northern Metro Manila because water released or overflowing from the reservoir can flow toward the Tullahan River system.
During an earlier monsoon episode this month, the dam actually exceeded its spilling level. On August 10, its water level reached 80.17 meters, slightly above the 80.15-meter spilling mark, prompting warnings for communities along the Tullahan River in parts of Quezon City, Caloocan, Valenzuela, Malabon and Navotas.
The current situation is different: La Mesa Dam is at Alert Level 3, but the latest official reading remains below the spilling level. Nevertheless, continued heavy rainfall could cause the reservoir level to rise again, making close monitoring critical.
Residents in low-lying and flood-prone communities are advised to keep track of updates from PAGASA and their local disaster risk reduction and management offices, particularly if heavy rains persist.
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