THE recent floods remind us that building an expressway above a major waterway exposes all of us to much higher disaster risk. One of the unforgettable images from this was that of several barges crashing into a bridge on the Marikina River. Experts are still determining whether the bridge’s structural integrity was affected, but the incident drove home the point that such structures are susceptible to damage from the impact of heavy debris and unmoored vessels swept down by a major flood. Even structures made of concrete and steel cannot withstand the force of objects with large mass and fast-moving water.
In many previous columns, I wrote about the destructive impacts associated with the Pasig River Expressway (Parex) such as worsening traffic, air and water pollution, urban blight, reduced green public spaces and diminished potential for tourism, recreation and economic activity along the entire river. One additional harm that we should recognize is that the Parex will likely paralyze the metropolis in the event of a collapse and hamper relief and recovery operations.
Consider this: the Parex, almost 20 kilometers in length, will be standing on 300-400 piers or pilings planted into the Pasig river bed. All it takes is for one pier to weaken and buckle — possibly during a flood or earthquake. A chain reaction could cause the collapse of several sections of the expressway or even the entire structure. With greater frequency of floods also comes increased risk of scouring — a process where the soil around piers are loosened and eroded by the flow of water, weakening the foundation of the structure over time.
A Parex collapse during a major earthquake or flood will likely make the Pasig River impassable by any type of vessel. Heavy concrete debris will completely block the river and prevent it from serving as an alternate route for moving emergency supplies and evacuating victims. Moreover, because the Parex is designed to be built above all the existing bridges crossing the Pasig, a collapse will very likely damage those bridges and additionally paralyze the flow of people and goods traveling between the northern and southern sections of Metro Manila.
The Parex’s earthquake and liquefaction risk is significant and cannot be ignored. Let me recount key points from an earlier column: “Liquefaction happens when loose and water-logged soils near the surface become less rigid and ‘liquefy’ during earthquakes. It is commonly associated with earthquakes near water bodies with many layers of loose sediments and soils underneath. In the last century, there have been four recorded incidents of liquefaction along or very close to the Pasig River.”
“The Revised Environmental Impact Statement (EIS) report for Parex, which is available on the website of the Environmental Management Bureau … mentions the high disaster risk that Parex will face. Most of the proposed expressway lies in a high seismic risk zone as well as in a high liquefaction hazard zone. Worse, a major segment of the Parex — the portion that crosses C5 — intersects with the West Valley Fault, a major earthquake source capable of generating tremors of magnitude 7.0 or greater.”
“In response to the apparent high disaster risk, the Parex revised EIS report only states that: Engineering solutions can be applied to prevent disaster risk such as driving the piles into the ground down to the depth of refusal to have a good and stable founding level. (Section 2.1.2.11.1, Impacts of Geologic Hazards and Planned Earthworks on the Project Facilities). The problem is that there is no information on the availability of safe founding levels for every section of the river and at which depths these can be found.”
“No geotechnical investigations have yet been conducted, according to Section 2.1.2.4 of the revised EIS report on Subsurface Conditions. This is a serious deficiency. The report explains that the desirable foundations for the piles are “relatively deep,” but it is not known how deep. The same report states (i) that drillings for Skyway 3 on the Pasig River have only yielded loose soils and soft clay [which are unsuitable] as deep as 9 meters; and (ii) that drillings for other projects in Manila Bay, or near the Pasig River have yielded only loose or soft soils as deep as 15 meters. It is well known that if loose sediments are deep and water-saturated, the ground motion during an earthquake will be more intense and severe.”
What all this tells us is clear. The future will likely bring more frequent and intense flooding, increasing the risk of heavy flood debris crashing into structures built on the waterway and of scouring damage to piers. Exacerbating this risk is the fact that the entire area sits on loose soil and is subject to liquefaction and earthquakes. The collapse of any section of the Parex will make the river unnavigable and obstruct emergency response and relief efforts. The project therefore undermines our disaster management and response capability, and places all of us at greater risk. Proceeding with the Parex makes no sense, even only for this reason.
Robert Y. Siy is a development economist, city and regional planner, and public transport advocate. He is a co-convenor of the Move As One Coalition. He can be reached at [email protected] or followed on Twitter at @RobertRsiy.
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