The Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) alerted local governments in Mindanao as it recorded an unusual rise in the water levels of rivers even before typhoon “Bising” (Surigae) entered Philippine territory on Friday, April 16.

It was the weather station in Misamis Oriental which noted the sudden swelling of rivers in northern Mindanao.

Hydrologist Victor Flores, a weather specialist at PAGASA’s Misamis Oriental station, reported the unusual increase in the water levels of rivers in neighboring Bukidnon province on Wednesday, April 14.

The Bubunawan River alone rose by 1.59 meters from 3:40 pm to 4:20 pm Wednesday as a result of a heavy downpour.

That, according to Flores, was unusual given that PAGASA only considers river swelling to be rapid once the water level rises by over 1 meter in an hour’s time.

“In the Bubunawan River’s case, it only took 40 minutes for the water level to rise by 1.59 meters,” said Flores, who also heads a group monitoring the Cagayan de Oro river basin.

The swelling of the Bubunawan River adversely affected Cagayan de Oro’s water supply. The river is a major source of the city’s tap water.

The adjacent Tumalaong River, also in Bukidnon, swelled by two-thirds of a meter or 0.61 meter in minutes starting at around 4:30 pm on the same day.

Flores noted that it rained hard in some parts of Bukidnon from 1 pm to 4 pm that day. PAGASA called it a “localized thunderstorm.”

In the Dahilayan area alone, also in the same province, PAGASA recorded 9.5 millimeters of rainfall in just 10 minutes. The state weather bureau considers 7.5 mm of rainfall in an hour’s time “heavy.”

Luz Mercado, another PAGASA weather specialist, warned that the trough of severe tropical storm could further make rivers in Bukidnon and elsewhere in Mindanao swell, and spawn flashfloods.

“We call for vigilance,” Mercado said.

Rivers swell, water supply cut

For at least 14 hours, Cagayan de Oro saw many faucets dry up after its tap water supplier reported that flashfloods along the Bubunawan River crippled its operations. In some areas, residents were inconvenienced as a result of very weak water pressure.

The Cagayan de Oro Water District (COWD) said its supplier of treated bulk water, the Pangilinan-owned Cagayan de Oro Bulk Water Incorporated (COBI), reduced its deliveries from 60 million liters to 40 million liters a day on Wednesday.

Ladelle Sagrado, COWD spokesperson, said the reduction significantly weakened the water pressure in the entire western area of Cagayan de Oro, and the Camaman-an and Bueno Oro areas in the east.

Sagrado said COBI sent notice about it being forced to cut the daily water deliveries by 20 million liters because the flashfloods caused its raw water intake at the Bubunawan River in Baungon town, Bukidnon, to clog up.

No repairs were carried out until the water receded to a safe level, Sagrado said.

She said worst affected affected were people in multi-story buildings and those living in elevated areas.

The water supply normalized at around midnight. – Rappler.com