Dredging may not be enough

At about the same time that former US Vice President Al Gore committed himself to his environmental concerns, my mind riveted to an alarming scientific forecast. I am far from being a technical person so I could only be alarmed that scientists projected, as a result of global warming, the irreversible melting of the polar ice caps. In plane language, mountain ranges of snow have become water. According to a report I read few years ago, such process would translate into the seawaters’ creeping from 7 to 10 feet into our shorelines.

I do not know if there was any relation between that dire environmental warning and the unusual inundation of many parts of Luzon caused by the few past tropical depressions. Typhoon Ondoy, two years ago and storm Pedring, last month, dumped huge volumes of waters submerging vast areas. But, on top of that, geologic authorities declared that the floodwaters, particularly in Bulacan, could not recede as quickly as they did many years ago. They attributed that phenomenon to the confluence of two events namely, the sinking of their land and the rising of the sea level. If the latter prognosis of the two events was correct, then the scientific projection of the seawaters eating into our shores could be well at hand, as a matter of fact.

Cebu City may not be spared of the same effects of climate change mankind is presently being confronted with. We have to face increasing volume of rainwaters and find ways to overcome the concomitant flooding. And it looks like the city leadership is attempting to address this. That is how we look at the multi-million project of His Honor Cebu City Mayor Michael L. Rama and, quite admiringly, of the city council. His administration has engaged many contractors to dredge the waterways of the city in the hope that floodwaters quickly flow towards the sea.

During the kalag-kalag days, we cruised along the boundary of the cities of Mandaue and Cebu at the North Reclamation area. Traffic slowed us down just as we were on the bridge. The sight was unpleasant. So much debris littered on the waterway that I could not help but curse those responsible for throwing them. Mud, where visible, parted the flow of water.

Then, we saw something more alarming. At the river’s end, the seawater met the mucky fresh water. Because the tide was rising then, it seemed to us that the flow of water was reversed. With the level of the sea apparently a little higher than the river, the salt water was going towards the city. Really, if there were floods that day, water could not exit toward the sea and the inundated areas would remain flooded.

The dredging, as planned by our leaders, must not be as simple as taking out the silt from the bed of the waterway. It would not achieve its objective of draining out water. If the alluvium and avulsion were to be taken from the mouth of the river, (and that is how I imagine the dredging be) its level would become lower than the sea itself such that water could not flow freely. Whoever said that water seeks its own level would, probably, stand by my side on this statement.

So, I assume that the dredging shall be complemented by other technical ways of warding the inward flow of seawater. A non-engineer like me would not know what it may be but yes, I imagine that the contractors must be planning to put in place a dike system not entirely different from that which is used successfully by the low lying countries composing the Benelux. The levees in New Orleans and Galveston were breached by the surge brought about by category 5 hurricane of late and that technology should not be employed.

 With a tall sea wall in place at the mouth of the river, a system of pumping the water over the dike and unto the sea is needed. This must be a major component of the project. Without it, I cannot imagine how the dredging could solve flash floods.