By Riza T. Olchondra
An underground spillway designed to speed up the flow of water from Laguna de Bay to Manila Bay can help ease the problem of flooding in lakeshore communities, according to the Laguna Lake Development Authority (LLDA).
The agency said in a statement that it has urged the government to prioritize the project which is expected to alleviate the massive flooding around Laguna de Bay, including Metro Manila, during the rainy season.
The “Parañaque Spillway” was originally conceptualized back in the 1970s along with the existing Napindan Hydraulic Control Structure and Manggahan Floodway.
However, the LLDA said it would have to modify the design since a conventional spillway was no longer feasible given the dense population and urban buildup at the proposed site.
It has instead proposed the construction of an underground tunnel which is designed to allow up to 350 m³/s of water to be discharged from Laguna de Bay into Manila Bay.
The tunnel will be passing through a narrow neck of land (7.2 km) westward from a point near Sucat, Parañaque City, on the shoreline of Laguna de Bay until Manila Bay.
According to the study conducted by the LLDA Project Development and Monitoring Evaluation Division, water buildup in Laguna de Bay during typhoons can be much better controlled with the underground spillway.
Without the project, the lake water level reduction is about 0.60 meters a month. This is expected to go up to 1.0 meter per month with the construction of the spillway, the agency said.
Secretary Neric Acosta, presidential adviser for environmental protection and LLDA general manager, said that the spillway should be done in combination with other measures to control flooding such as improved catchment management, creation of a floodplain storage in the Marikina catchment as well as the dredging of Pasig River, Napindan Channel and small tributaries surrounding the lake to ease water flow.
“We should look into a more long-term and holistic approach to flood control and disaster mitigation,” Acosta added. “This would involve rehabilitating the watershed through aggressive tree-planting, resettlement of households that are vulnerable to flooding, propagation of proper waste disposal through materials recovery facilities and the installation of a flood warning system,” he said.
The Parañaque Spillway project was revived following torrential rains spawned by the monsoon which inundated a huge part of Metro Manila more than two weeks ago.