People navigate the flood in different ways as intense rain brought by tropical storm Enteng inundates large portions of Cainta, Rizal on September 2, 2024. Jonathan Cellona, ABS-CBN News

MANILA — The Department of Environment and Natural Resources (DENR) said on Thursday it would too much of a “stretch to say that most of flooding in Marikina and other cities in Metro Manila is because of quarrying” alone.

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In a press conference, DENR Undersecretary for Integrated Environmental Science Carlos Primo David explained that various factors must be looked at, which are equally if not more contributory to the perennial flooding in many parts of the country, particularly the eastern portions of Metro Manila.

At the top of the list is the intensity and duration of rainfall. Naturally, rainfall follows two courses — infiltration or runoff. Infiltration happens when water is absorbed by soil while runoff is accumulated water on the surface of an area of land that flows to find a means to drain away.

In a span of 48 hours, Tropical Storm Enteng brought rain volumes of over 320 millimeters in the PAGASA weather station in Tanay, Rizal. While it pales in comparison to Typhoon Ondoy in 2009 which brought over 330 millimeters of rain or the more than 350 millimeters of rain by Typhoon Ulysses in 2020, a lot of areas especially those inside the Marikina River Basin were quick to become inundated.

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The Marikina River Basin spans several municipalities in Rizal on the east and cities of Metro Manila in the west including Quezon City, Marikina, Pasig, Taguig, and the municipality of Pateros.

Modeling from the DENR shows how these areas, because of development and human settlement, have been heavily covered with cement roads, residential areas, commercial establishments, and other concrete infrastructure, which have no capability to absorb rainwater.

The dire state of bodies of water, primarily the Marikina River which spans a total length of 66 kilometers, is also among the reasons why flooding in this portion of the country occurs.

“When it is heavily silted, its capacity to absorb water is reduced. And when we build long rivers and constrict our river channels, this produces huge implications to flooding,” David said.

By constricting river channels, what David is pertaining to is building roads and pathways along the riverbanks or even erecting homes.

In urbanized areas, the environment official said that only 10 percent of rainwater will actually infiltrate the ground while 90 percent becomes runoff. Urban areas and quarries, David explained, have the same effect on rainfall — both do not absorb water and therefore contribute to surface runoff.

But quarries, according to the DENR, do not make a big dent as far as flooding is concerned.

NO QUARRY SITES INSIDE PROTECTED AREA

The agency said there were at least 7 quarry operators inside the Marikina River Basin. But none of them are operating within the Upper Marikina River Basin Protected Landscape (UMRBPL).

A map from the DENR showed that quarry sites are located in portions of Rodriguez and San Mateo, which have been operating in the last two decades. Overall, the quarries are said to span 350 hectares of land out of the over 43,000 hectares of the Marikina River Basin outside of the UMRBPL.

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Despite this, David said the problem of flooding could not be blamed only on quarrying alone.

“if we continue to harp on ‘ay quarrying ang problema diyan’ (quarrying is the problem) we will never see the actual reasons for flooding in Metro Manila,” he said.

David reiterated that total ban of quarrying is currently in effect in the UMRBPL and no permits exist. However, no moratorium on the issuance of permits for quarries outside the protected area has been issued nor is there a policy to issue a moratorium.

The DENR said the public should understand that putting an end to quarries would have economic implications, hence the need to strike a balance in terms of need and impact.

“We should recognize that the quarries there also serve a purpose. Where will we get gravel and sand if there are no quarries. We can shut all of them down but I assure you prices of sand and gravel will rise because we will be culling from other areas,” David said.

David suggested that the agency to call and gather all quarry operators to ensure that not only are they compliant to standards but are also exerting effort to mitigate the effects of their operations.

“My suggestion is to call on our quarry operators, not to scold them or investigate, but to actually work with them in ensuring that they are not contributing to local flooding and perhaps even device or implement programs within their companies to mitigate flooding via having their own impounding systems,” he said.

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