By Engr. Edgar Mana-ay
The opening of the seven flood gates of Magat Dam is now a subject of intense complaints from the populace especially in Tuguegarao City, Cagayan province which they believed was the cause of the worst flooding in memory.
Even Congress, as a response to the people’s complaints, will be conducting an investigation IF THE CORRECT AND PROPER PROTOCOL WAS FOLLOWED IN THE OPENING OF THE SLUICE GATES OF MAGAT DAM.
Cagayan Province including its capital Tuguegarao City experienced unprecedented flooding last November 11 to 14 in the aftermath of Typhoon Ulysses, even worse than the 1970 flood that they considered the worst in memory.
24 municipalities plus Tuguegarao City was almost completely submerged displacing 11,392 families making Cagayan Province look like an ocean, according to Governor Manuel Mamba.
The severity of floods is rated in years that it will cyclically occur. According to experts, this flood is a 100-year flood, meaning it occurs once every 100 years. A confluence of natural hydro-geological events such as a series of typhoons that brought tremendous rains to fully saturate the entire ground of the province, then as a climax, a very heavy downpour brought by Ulysses of 111.4 mm rain for a 24-hour period on November 11.
The last heavy rain (which in normal times is good for a month but delivered in just one day) cannot anymore be absorbed by a fully saturated ground due to the recent past three typhoons, hence almost all of it will become over land flow where existing drainage to direct it towards the sea (streams, tributary rivers, canals and the mighty Cagayan river) cannot handle. All these drainage systems were overwhelmed resulting in such widespread flooding. Some say that this confluence of natural events is an act of God himself.
But it cannot also be denied that man himself is the primary cause of this disaster. Tuguegarao City is the last station of the mighty Cagayan River, the biggest river in the country that drains rainwater from as far as Nueva Viscaya, Ifugao Province, Isabela, Cagayan and other places. Magat Dam is located on Magat River in Ramon, Isabela province and JUST ONE of the major tributaries of Cagayan River. There is devastation of forests in all these watersheds whose rainfall will finally be delivered by the Cagayan river towards the sea.
We go back again to the often-misunderstood basic functions of trees. The leaves of trees ACT AS A CUSHION TO RAINFALL so that it will fall slowly to the ground for increased infiltration and less overland flow. This is further enhanced by the undergrowth of shrubs and bushes plus the pileup of decaying leaves, a result of keeping the forest away from human touch. But this is not anymore the case because slash and burn farming (kaingin), illegal logging, using the forest as boy scout jamboree sites have truly devastated our watershed resulting in mass siltation and sedimentation of all waterways.
By the way, mining has nothing to do with it, as in underground mining which has nothing to do with surface condition, while open pit mining even acts as a temporary reservoir in an abnormal heavy downpour.
We go to the Three Gorges Dam in China designed to tame the largest river in China, the Yangtze river. Three Gorges dam is so large that it can be seen from space, costs $28.6 billion, generates 22,500 megawatts of electricity more than enough to power the Philippines (15,000 mw).
Last June during a 60-year flood, dam management had opened its sluice gates since the dam reservoir cannot handle the influx of floodwater upstream, otherwise, the dam will overflow and will be destroyed creating unimaginable damage downstream. Areas downstream of the dam bigger than the size of Mindanao were totally flooded resulting in 158 death, affecting 55 million people with damage at $20.5 billion nearly the cost of the dam itself.
Investigation by Chinese hydrologists showed that during a 100-year flood, more than 120 billion cubic meters of water equivalent to the waters of the Dead Sea in Israel will have to pass the Three Gorges Dam in one-month time.
The storage capacity of its reservoir is only 5% of that volume of the water, hence there is NO OTHER RECOURSE BUT TO OPEN THE FLOOD GATES INCREASING THE FLOODING DOWNSTREAM. Pareho man ina sa Magat Dam, kon maglapaw ang tubig, marumpag ang dam mas daku ang damage, hence its really DAMN IF YOU DO AND DAMN IF YOU DON’T!
We go back to our very own ongoing P11.2 billion JRMP II Dam construction at Calinog, Iloilo designed to irrigate 32,000 hectares of rice lands in towns downstream of the dam. Mostly financed by a Korean bank, it is being constructed by a Korean company with a Korean technical consultant, Dasan Consultant.
We give the benefit of the doubt that Dasan Consultant had performed a satisfactory geotechnical investigation of the area despite the tsismis that there is an active fault line in the area because Dasan has declared it safe to construct. I call it tsismis because this writer being involved in a very complex geo-tech work of fault-finding (not the fault that is in your mind) investigation in the mining industry knows it requires lots of high tech work to conclude that there is a fault in an area and, determining as to whether it is minor or major and then whether it is active or inactive.
During the process of geo-tech work of Dasan Consultants, NIA and the Provincial Government FAILED to provide an oversight or auditor function who should have looked over the shoulders of the Koreans to see if what they are doing conforms to the standards in dam investigation. Just like in the case of Magat and Three Gorges Dams, is the size of JRMP II Dam reservoir enough to handle a 60-year flood considering that the watershed upstream is as devastated just like any watershed in the country. If it is of any consolation to the Filipinos, NO dams in the whole world failed because of an earthquake due to a fault rupture. The St. Francis Dam in Los Angeles failed in 1928 causing 400 people to perish because the ground below the dam became unstable due to water saturation and the dam toppled over.
It is strongly suggested that the National Irrigation Administration (NIA) and the Provincial Government call for a public hearing where all concerned are present, the Governor, Board members, PENRO, Provincial Engineer, and other technical private citizens.
Let the Korean Dam Contractor and Consultant explain and provide the assurance that in case of a 60-year flood, the dam will be an asset in mitigating flood instead of a liability of increasing the flood. For according to Stanislaw Leszczynski (1677-1778): To believe with certainty we must begin with doubting.
