By CESAR JOLITO III

The Department of Environment and Natural Resources in the Negros Island Region (DENR-NIR) has attributed the massive flash floods that devastated multiple towns in Negros Occidental during Typhoon “Tino” on November 4 to an extraordinary volume of rainfall and the blockage of major waterways by boulders, debris and uprooted trees.

DENR-NIR Director Charlie Fabre said their initial assessment shows that several rivers and tributaries could no longer hold or redirect the sudden surge of water after being obstructed by large logs and rocks, causing floodwaters to spill into communities.

Citing data from Pagasa, Fabre said the province experienced an alarming 250 millimeters of rain within just two days — an amount equivalent to or greater than an entire month’s rainfall under normal conditions.

“The volume of water was simply too heavy … In the Philippines, 200 to 400 millimeters is the monthly average, but during the typhoon, that amount fell in only 48 hours,” Fabre said.

Loose soil on Kanlaon slopes fueled debris flow

The DENR’s rapid assessment in severely affected areas — La Carlota City, La Castellana and Moises Padilla in Negros Occidental, as well as Canlaon City in Negros Oriental — revealed that loose, unstable soil along the upper slopes of Kanlaon Volcano played a major role in the destructive flow of debris.

Fabre said frequent earthquakes, combined with continuous rains prior to and during the typhoon, weakened the soil structure. This triggered landslides and uprooted trees along riverbanks, which later surged downstream with the floodwaters.

The presence of large logs and boulders in lower communities, Fabre noted, showed that waterways became severely clogged. In some sites, Fabre said that instead of bridges, box culverts were built — structures more easily blocked when debris accumulates.

“If big trees and logs clog these culverts, water has no choice but to carve a new path. That’s what happened in several barangays,” he explained.

DENR probes possible illegal logging

While DENR found no chainsaw marks on the fallen trees, the agency is not ruling out illegal logging as a contributing factor.

Fabre said the investigation is ongoing and stressed that anyone found to be engaging in unlawful forest activities on the volcano’s slopes will face criminal charges.

Authorities involved in the clearing operations have collected large volumes of logs and tree debris from the affected localities.

Fabre said these materials will be repurposed for the rehabilitation of damaged public facilities as communities begin recovery efforts.

The DENR is preparing a more detailed geologic hazard report to guide long-term mitigation strategies and prevent similar disasters in the future./CJ, WDJ