The flashflood that killed and harmed hundreds of people in the northern Mindanao and southern Visayas areas was aggravated by the reported collapse of dams along the Cagayan de Oro River, according to the Department of Science and Technology Secretary Mario G. Montejo. Montejo was with the presidential party devastated by flashfloods wrought by Tropical Storm Sendong.
“It is most likely that the flashflood in Cagayan de Oro was caused not only simply by the high volume of rain that fell in the watershed of rivers in said places but essentially of the reported collapse of dams at the upper parts of the rivers,” Montejo announced.
Reports from the field that reached the presidential party regarding the collapse of the dams are being investigated, per instructions of Pres. Benigno Aquino III.
“Pagasa had been doing its job conscientiously,” Montejo assured. “In fact, places such as Bohol, Surigao, and Camiguin that heeded Pagasa’s warning and took appropriate actions had mitigated the effects of Sendong.”
To further improve its weather forecasting and hazard mitigating capability, Montejo said that Pagasa in 2012 will upgrade monitoring systems.
“We are set to install 1,000 water level sensors in selected major river basins in 2012,” Montejo revealed. “Since the 1980s, only four rivers were installed with sensors to measure water-level rise. The President has given instructions and allotted resources to fast-track our river monitoring system nationwide to aid in forecasting potential floods.”
“To enhance rainfall and weather forecasting, we will also improve the integration of data from Doppler radars, satellites, automated weather systems, and rain gauges through numerical model WRF,” he added.
DOST is also looking at enhancing its flood forecasting system to determine expected impact to local communities. This includes the use of several techniques such as the use of 3D maps.
On the reported dam collapse, Sec. Montejo said that the continuous rains may have caused the accumulation and build up of water upstream of the dam.
“At some point, the dams may have collapsed when the trapped water filled with debris overtopped the dam. This could have led to dam breakage and failure,” Sec. Montejo
When the large volume of water trapped behind the landslide debris dams was released, it triggered the flashfloods. The landslide dam break mechanism caused the flashfloods, which would explain the sudden surge of water reported by survivors in Cagayan de Oro,” Montejo added.
Sec. Montejo pointed out that survivors described the flashfloods as “sudden surge”, while post-disaster pictures showed large amounts of mud and debris, including trees, that were carried by the flashfloods.
He also clarified that although the rainfall brought by Sendong was not like Typhoon Ondoy that generated181 mm of rain for one day that caused the disastrous flashfloods in 2009. The landslide dam break that happened in Sendong had happened during the 2004 Infanta, Quezon and 2008 Iloilo flashfloods, he said. S&T Media Service