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MANILA - The National Disaster Risk Reduction and Management Council said Tuesday dams would break if it did not release water to prevent overtopping.

"'Yung paglalabas po ng tubig ng isang dam it is also a disaster-mitigation measure. Kapag hindi po natin binawasan ang tubig, sa tindi ng pressure at punong-puno na ang dam pwede pong mawasak. Flashflood ang problema d'yan sa community kapag di tayo nagpalabas," NDRRMC spokesperson Mark Timbal told ABS-CBN's Teleradyo.

(Releasing water from dams is also a disaster-mitigation measure. If we don't release water, the dam may break due to the pressure and water level. It will result in flashfloods in communities.)

• Magat Dam reduces spilling operations as Cagayan Valley sees historic floods
• What causes severe flooding in Cagayan province?

Cagayan Governor Manuel Mamba earlier blamed the heavily-silted Cagayan River, Typhoon Ulysses' rainfall from nearby provinces, and water release from Magat Dam for the massive floods that submerged the province and left at least 9 dead.

• 9 dead in unprecedented 'late' floods in Cagayan; rain washed down from nearby provinces- Gov

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"Convergence ng maraming factors po ito. Ang nag-exacerbate is the dam, 'yung papapakawala (ng tubig). Di naman namin nile-lay yung blame sa dam solely sa kanila lang," Mamba said.

(It was a convergence of many factors, what exacerbated it is the dam's water release. We're not laying the blame solely on them.)

Fernando Siringan, former director of the University of the Philippines Marine Science Institute (UP-MSI), said Cagayan serves as a catch basin of water from surrounding mountain ranges.

Both water and sediments from the mountains cause the rivers to overflow, prompting floods, Siringan said as flooding inundated large parts of Cagayan Valley in the wake of Typhoon Ulysses (international name: Vamco).

• INFOGRAPHIC: Dams and floodways to watch

The Cagayan River also becomes narrow in the portion of Sicalao Ridge because of old and deformed sedimentary rocks.

This narrow portion of the river starts at Barangay Tupang in Alcala, Cagayan and ends at Magapit in Lal-lo town, according to Siringan.

"Ang mahabang makipot na channel ng Cagayan River ay nakapagpapabagal sa pagdaloy ng tubig papunta sa bukana ng ilog sa Aparri. Dahil bumagal ang daloy ng ilog, naiipon ang tubig sa kapatagan, umaapaw sa channel at nagbabaha," he explained.

A 1987 study from the Japan International Cooperation Agency (JICA) on the flooding in Cagayan Valley, Siringan said, recommended the widening of the narrow portion of the Cagayan River from Alcala to Lal-lo.

But the scientist noted that the recommendation had yet to be fulfilled until now.

Meanwhile, the NDRRMC said it was studying a proposal to be the authority in deciding dams' water release following record flooding in Cagayan and Marikina.

The suggestion came from mayors as constituents complained of high level of floodwaters following Typhoon Ulysses' onslaught.

• Mayors want NDRRMC to authorize dams' water release: DILG
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"Ang suhestiyon pong 'yan ay pinag-aaralan natin para makita ang feasibility kung kakayanin mag-handle ng ganyan," Timbal said.

(We are studying that suggestion to see its feasibility, if we can manage to handle it.)