Only 10 days after the landfall of Typhoon Rolly, the Philippines was struck by another typhoon called Vamco, locally known as Bagyong Ulysses. Like Rolly, Typhoon Ulysses brought catastrophic winds and intense rains, causing flooding and landslides in CALABARZON. It developed from a low-pressure area (LPA) in the east of Mindanao to a tropical depression on November 8, 2020, and later intensified into a typhoon three days later. It made its first landfall at around 10:30 PM on November 11, 2020, in Patnanungan, Quezon, and its second one at around 11:20 PM over Burdeos. At its third landfall over General Nakar, it already reached maximum sustained winds up to 155 kph with a gustiness reaching up to 255 kph, speeding up to 20 kph as it moved west-northwest. This Office made its Operations Center into an Emergency Operation Center (EOC) that day to thoroughly keep track of the effects of the typhoon in CALABARZON.
To keep everyone in the region posted, this Office disseminated barangay listings of flood and landslide susceptibility ratings all over CALABARZON. Due to the previous typhoons, namely Rolly and Siony, the vast land of Sierra Madre was already saturated. This caused more severe flooding and landslides in CALABARZON and the National Capital Region by the time that Typhoon Ulysses entered the Philippine Area of Responsibility.
The devastating consequences of Typhoon Ulysses were felt by all provinces in CALABARZON. In the province of Cavite, some municipalities only had ankle-deep flooding, whereas some, like Bacoor, experienced up to 12-foot-deep flooding. There was also a reported landslide in the municipality of General Mariano Alvarez, caused by the heavy downpour of rain and very strong winds. Toppled structures such as electric poles caused unpassable roads in Silang.
In the province of Laguna, the deepest flood reported was in the municipality of Famy, where chest-deep flooding was experienced right after the landfall of the typhoon. There were also landslide incidents in the various municipalities this time, including Calauan, Cavinti, Nagcarlan, and Pangil. There was also a minor landslide in Calamba City.
The province of Batangas experienced the greatest number of landslides. In Batangas City, STAR Tollway-Pinamucan Bypass Road was closed due to collapsed stone masonry, grouted riprap, and cement-treated base (CTB). Some were already cleared such as that in a national road in the municipality of Cuenca, but some are still unpassable due to the debris. Flooding incidents were also reported. In the municipality of Agoncillo, the causes of flooding were carriage settlement due to the previous eruption of Taal Volcano and damaged pavement due to scouring of seawall protection. In San Nicolas, new fissures formed and existing fissures widened, affecting residential areas in Brgy. Calangay and Brgy. Bangin. The widening and deepening of these fissures were caused by oversaturation and erosion of the seeping rainwater brought by the typhoon.
The hardest hit in Quezon province was the flood-prone municipality of Lopez, where the intense rainfall caused floodwater in Brgy. Maguilayan to almost reach the roofs of the houses. Houses in Brgy. San Roque were even fully submerged partly due to the overflow of Talolong River. Landslides were also reported in the province. In Calauag, Mauban, Mulanay, Real, San Narciso, and Tagkawayan, the landslides that occurred caused trees to topple and soil debris to cover parts of their roads, making them unpassable. Tension cracks were observed in San Narciso.
In the province of Rizal, most of the municipalities experienced flooding. The swelling of Laguna de Bay caused heavy flooding in the municipality of Angono. The oversaturation of Sierra Madre led to more surface run-off along the headwater of Wawa Dam reaching the lowland, specifically the low-lying areas of Montalban, San Mateo and Marikina City. Evidence of this can be found in Barangay San Rafael where the overflow of riverine water destroyed several houses situated along the river embankment. Other parts of Rizal experienced major floods as well including Antipolo City, and Cainta, where residents from Brgy Sto. Domingo had to be evacuated due to the four-meter-deep flood. In some barangays of Rodriguez, the flood was so deep that only roofs of one-story houses were visible. Stranded residents had to be rescued from the top of the roofs. Landslides were reported in Cardona, Morong, and Tanay.
With this, assessments shall be conducted by this Office in flooded and landslide-hit areas of CALABARZON. Results from the said assessment shall be shown in a detailed 1:10,000 scale Rain-Induced Landslide and Flooding Susceptibility Map of the concerned municipalities and the Landslide and Flooding matrix of this Office.
Source: Liz Tan’s Facebook post.
[L] A slump with 3 meters depth was reported in Doña Aurora, Calauag, Quezon; [R] Aerial view of Catanauan, Quezon submerged in 1-2m of flood depth.
By : Engr. Patrizia S. Benedicto | 18 November 2020