Delayed dam project could have saved city from Sendong

(First of 2 Parts)

By MIKE BAÑOS, Editor-at-Large

A HYDROELECTRIC power dam project on the Cagayan River that has been delayed for 15 years running could have possibly mitigated the deadly flash floods which ravaged Cagayan de Oro City some four years ago and killed thousands of residents.
“The Bulanog-Batang Hydroelectric Power Project has a huge 82-million cubic meter reservoir impounding area,” said Engr. Cerael C. Donggay, president and CEO of Greenergy Inc. during a project presentation to the City Tourism Council held Tuesday, 10 February at the City Mayor’s Office conference room.
“With adequate warning, we can release water from our reservoir to accommodate a huge volume of flood waters coming from the Bulanog and Batang Rivers which at the very least, could have mitigated the deadly flash floods which killed thousands of people during the Sendong disaster,” he said.
A weather specialist of the Philippine Atmospheric, Geophysical & Astronomical Services (PAGASA), who was previously assigned with the agency’s post-event assessment team in Misamis Oriental following a storm surge event, affirmed this but requested anonymity.
“The 82 million cu.m. storage, I think is just large and somehow, Sendong is not the only baseline, if ever consider a higher threshold of capacity,” he said.
In comparison, he cited how the Pantabangan dam’s reservoir has a gross capacity of 2,996,000,000 cu. m., the biggest in the country (Bulanog-Batang has 2.7% of this capacity). The Angat dam’s reservoir has a gross capacity of 850,000,000 cu.m. (10 times bigger than Bulanog-Batang) with the La Mesa Dam reservoir at 50.5 million cu. m. the closest to it in size.
“Angat dam always releases its water during flood season,” he added. “Pantabangan and Angat are both ‘in-basin.’ Somehow, the construction of the dam will mitigate/minimize the effect of flash floods/flooding in the downstream area of Cagayan river than without the dam as compared.”
Tropical Storm (TS) Sendong (International name: Washi), which has been reclassified as a “severe tropical storm,” was the second tropical storm to hit Mindanao in 2011 and the 19th tropical cyclone that entered the Philippine Area of Responsibility (PAR) in the same year.
The Lumbia PAGASA Station recorded a one-day rainfall of 180.9 mm which is higher than the monthly average of 117 mm during December in the period 1977-2005.
The huge rainfall and steep slopes of surrounding peaks compounded the destructive power of the flash floods.
The following figures show the rainfall measurements in Talakag station during 1-hour, 3-hour, 6-hour and 24-hour periods:
Maximum Rainfall Intensity Talakag station:
• Maximum 1-hour 60.6 mm
• Maximum 3-hour 112 .0 mm
• Maximum 6-hour 199.0 mm
• Maximum 24-hour 230.5 mm (Dec 16, 2011)
In Capehan station, upstream of river Bubunawan (a tributary of Cagayan river), the 24-hour precipitation recorded on 16 December 2011 was 475 mm.
The huge quantity of rainfall that fell on the Cagayan river basin was most likely due to the orographic effect (relating to mountains, especially with regard to their position and form) caused by the mountains which hemmed in its tributaries upstream.
Rainfall estimates from NASA’s Tropical Rainfall Measuring Mission (TRMM) satellite, near-real time Multi-satellite Precipitation Analysis (TMPA) at the NASA Goddard Space Flight Center, Greenbelt, Md. were compiled for the period of Dec. 13 to 20, 2011 for the southern Philippines. TRMM is a joint mission between NASA and the Japanese space agency JAXA.
Rainfall totals are on the order of 200 to over 250 mm (~8 to 10 inches) along Mindanao’s east coast where Washi made landfall, but the highest amounts are along the northwest coast, where totals are on the order of 300 to over 400 mm (~12 to over 16 inches). (Steve Lang/SSAI/NASA’s Goddard Space Flight Center, Greenbelt, Md.)

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