Catch basins for floodwaters
Let us now accept the fact that Laguna de Bay will not be dredged of silt and water now or beyond 2016. So let us look into an alternative solution to flooding.
There will be flooding in Metro Manila every time there is heavy rain. Why? Because Laguna de Bay is already full.
Before the “Habagat” flood of August 2012, I already noticed the high water level in Laguna de Bay. During the “Habagat” flood my children left Provident Village on the morning of Aug. 7 when the river water started to “backflow” into the village. I chose to stay behind to monitor the situation. I was trapped inside our house for three days.
Provident Village’s perimeter dike was not breached even when the river water level rose to 20.31 meters. The floodwater rose “lampas tao” inside the living room of our house. The culprits: the diverted drainage pipes (2×48 inches) which allowed floodwater to “backflow” because there were no gates; and the two big flood pumps operated by the government, which were not working.
Contrary to claims that the Manggahan floodgates were opened during the “Habagat” flood, the Marikina River water level—as reported in the website of the city government of Marikina during the flood (Aug. 6-7) and after the flood (Aug. 14-Sept. 25)—showed otherwise. The water levels at Rosario and Angono after the flood were practically the same because the floodgates were opened, while there was an almost 3-meter difference in the water levels in Rosario and Angono during the flood, signifying the floodgates were closed. I cannot fathom why the floodgates were closed contrary to the established purpose of the Manggahan Channel vis-à-vis the Laguna de Bay Flood Control System.
We looked also into the question why there is a backflow of saltwater from Manila Bay during high tides when the water level at the Laguna de Bay drops to lower than 10.0-meter mark, and why the floodwaters at Laguna de Bay and Marikina River were not draining to Manila Bay as fast as we expected, even at the elevation of 13.0-14.0 meters above sea level. We found out that the gradient is only 0.04 percent (10 meters in 25 kilometers or 1 millimeter in 2.5 meters). So the flow rate is barely noticeable.
Dredging Laguna de Bay is now out of the question and we really cannot expect to drain the lake via the Napindan Channel at such a minuscule flow rate, we have to look for an alternative optimal solution that can be done fast. Why not install flood pumps at the Napindan and Manggahan floodgates and control the water level inside Laguna de Bay by pumping out excess water and making room for heavy rainfalls, while maintaining a certain level for use as potable water supply and for sustainable food production?
If we do it now, through emergency purchases, use of calamity funds, realignment of budgets, pulling out idle pumps at the MMDA and DPWH pumping stations and even calling for private initiatives, we can right away alleviate the sufferings of the still flooded lakeshore residents and give hope to a better future to the flood victims.
That’s President Aquino’s call now.
—ARISTON M. DAWANG JR.,