Land subsidence is a significant yet subtle threat that Metro Manila is currently facing, with irreversible consequences and long-term impacts if left without proper monitoring and preventive measures. It happens due to the sinking of the ground surface due to subsurface movement of earth materials.
However, the primary causes of major flooding in Metro Manila have always been attributed to poor garbage management, inadequate infrastructure, and a general lack of discipline, despite Land Subsidence being recognized as one of the hazards that threaten the area since the 1990s.
So, what are we missing?
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The Silent Enemy
Data since 2014 show that areas in Metro Manila are sinking by as much as 109 millimeters per year. For comparison, the next largest amount of subsidence in the country is Metro Davao, which is sinking at only 38 millimeters per year.
One of the major factors contributing to faster land subsidence is the improper placement and/or regulation of groundwater throughout the country. This irresponsible usage of groundwater pumps can lead to street flooding, cracking of major roads, and the contamination of fresh groundwater. Simply put: When too much groundwater is pumped out, the ground dries out and sinks.
Satellite data from Sentinel-1 also shows sinking rates of 2-4.2cm/year between the years 2003 to 2011 in Manila and surrounding cities, directly correlated with heavy groundwater pumping. In fact, there is still no official count of “poso” or hand pumps in Metro Manila as of this article’s writing.
The city’s dense population and lack of proper urban planning have also made it harder to manage both land and water use, creating a perfect storm for disaster.
What Can Be Done?
Land subsidence in Metro Manila isn’t a distant threat. It’s happening right now, silently and at alarming rates. With continued sinking, even moderate rain or tidal events could become major floods. And if left unchecked, it could eventually lead to an even more crippled economy due to damaged infrastructure and groundwater supply contamination nationwide.
Thus, we must push for proper regulation of groundwater use, responsible water collection and conservation, and the dutiful monitoring of land subsidence in our country in order to decrease the risk of floods, building and infrastructure damage, or worse.
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