What caused the worst flooding in the Cagayan Valley in 40 years?

MANILA, Philippines – Authorities offered several explanations Saturday for the worst flooding to hit the Cagayan Valley in 40 years.

Being a catchment basin, water from other provinces and the water released from the Magat dam flowed into Cagayán, causing the flooding, Cagayán Governor Manuel Mamba said.

The National Irrigation Administration (NIA) said it has been releasing water from the dam since Nov. 9 before Typhoon Ulysses (international name: Vamco) hit, and then opened seven of the Magat spillway gates to control the overflow. of the reservoir at the height of the typhoon.

Wilfredo Gloria, operations manager for the Magat River Integrated Irrigation System, told the Inquirer that the NIA could not completely stop the release of water because that could result in more massive destruction as the water level in the dam was at a critical point.

He said in a telephone interview that five of the spillways had been closed and only two doors remained open on Saturday, discharging 1,355 cubic meters per second of water against an inlet of 1,261 cm per second.

Overload Hazard

This is to stabilize the water level of the dam which currently stands at 192.19 meters, compared to the critical level of 193 m, Gloria said.

“What we want is to normalize the water level at 192 m or at least below 193 m, but we must also take into account the communities that may be affected by this. So right now, as far as possible, we are trying to stabilize it, “he said.

“If we overload the tank up to 193 meters, it can lose its natural stability. If we overload the dam and that overload continues, the dam can break, ”added Gloria.

The irrigation and hydroelectric dam was built in 1982 on the edge of the town of Alfonso Lista in the province of Ifugao and the municipality of Ramon in Isabela. It has a 45-square-kilometer reservoir that is fed by the Nueva Vizcaya (60 percent), Ifugao (33 percent) and Isabela (7 percent) watersheds.

The NIA recorded that from Monday to Saturday, the reservoir of the multipurpose dam had an inflow of 721.28 million cubic meters of water while the output totaled 578.33 mcm.

Downstream flow

Ed dela Cruz, a hydrologist with the Philippine Atmospheric, Geophysical and Astronomical Services Administration (Pagasa), said the inlet water flow was about the same as the water discharge at 1,271 cm: 862 cm of water for spills and 409 cm. cms for power generation.

“The entry of water to the dam must be reduced so that at least the power generation and the entry are equal. Then they could close the doors, ”he said.

Water continues to flow into the dam from its 4,100-square-kilometer catchment basin, Dela Cruz said.

“Ulises had a large band of rain that reached Cagayan and that rain is entering the expansive basin,” he said.

Dela Cruz said that another factor that caused the flooding was water from the upper parts of Cagayán that flows downstream to the Cagayán River.

Mark Timbal, spokesman for the National Disaster Risk Reduction and Management Council (NDRRMC), said the widespread flooding in the Cagayan Valley was not due to the release of water from the Magat dam, but rather to the rising of the Cagayan River over the course of several weeks.

“These flood incidents are the cumulative effects of the continued rains experienced in Luzon,” Timbal told the Inquirer.

He explained that there have been “more than a month of rainy days,” in addition to at least five successive tropical cyclones that soaked the Luzon landmass.

Timbal said that rains from previous storms and typhoons have caused all tributaries of the Cagayan River to swell, leading to flooding. The release of water from the dam was also a factor.

In October 2015, at least 26 villages in Cagayan were flooded due to the spill of water from the Magat dam in Isabela after the slow tropical storm “Lando” (Koppu) that flooded and caused landslides in many provinces in the north and center of Luzon.

NDRRMC CEO Ricardo Jalad insisted that the council gave proper flood warnings.

Surprised local governments

He said the agency’s notices were the same as Pagasa’s “and always highlight the risk of flooding,” Jalad told reporters in a Viber message.

He also said that the bodies in charge of assessing risks due to hydrometeorological hazards are Pagasa and the Bureau of Mines and Geosciences.

Malacañang said on Saturday he was not unprepared for the massive flood that quickly washed away the Cagayan and Isabela provinces in the wake of Ulises, even though local officials were surprised by its unprecedented magnitude.

Many Filipinos who were following relief and rescue operations in typhoon-hit areas, especially Metro Manila and Rizal province, heard reports of the massive flooding in the two northern provinces only late on Friday night and the Saturday morning.

But presidential spokesman Harry Roque said the National Council for Disaster Risk Reduction and Management had already deployed relief supplies and rescue personnel to the region.

“We were not caught off guard because what we needed had been previously placed. We just deployed more air assets in the area, ”Roque said in the Laging Handa report.

He said the Philippine Coast Guard (PCG) has been rescuing residents in Isabela and Tuguegarao City since dawn Friday.

Early Saturday morning, the PCG also deployed convoys with a multipurpose vehicle, trucks, buses, newly acquired rubber boats and rescue personnel, Roque said.

“The president is aware of the situation,” he added. “He is in constant communication with [Defense] Secretary Delfin Lorenzana and Undersecretary [Ricardo] Pull the [NDRRMC]. “

In the same briefing, Mamba said that the flood water level rose to 13.1 m, higher than the 11 meters it had reached in the past.

“This is unprecedented in Cagayan, it is the first time we have experienced this. That is why many were surprised. But really, we prepare for this, but this is worse than what we prepare for, ”Mamba said at the Laging Handa briefing.

—With reports from Leila B. Salaverria, Patricia Denise M. Chiu, and Inquirer Research

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