Metro Manila is composed of 16 cities and 1 municipality it is situated atop a wide flood plain that is considered as one of the biggest in the Philippines. A flood plain is an expanse of flat, level land situated among streams or rivers that naturally overflow during sustained rainfall. In the case of Metro Manila, the main river (Pasig river) is filled with tributaries and canals that branch out in various cities and towns. There are two major tributaries, the Marikina River and San Juan River.
When the Spaniards established what is now the City of Manila in the late 16th century, they enlarged existing settlements that were river-based. In fact, the established name for the locals, Tagalog, is derived from the native words taga and ilog, which means “of the river”. There were said to be around thirty-five riverine extensions of the Paisg River in the area, known as esteros. These esteros contained a mixture of fresh water from the river and salt water from Manila Bay, and were much used for transportation back then. More importantly, these waterways served as a natural floodway to drain excess water during the dreaded typhoon season. However, by the latter part of the 20th century, much of the esteros fell victims to rapid industrialization and modernization. Residents and transients turned the canals into catch basins for garbage. Factories, plants, and industrial establishments also dumped their waste into the waters. And unchecked urban development encroached on the waterways, some of which were deliberately narrowed or filled over.
As a result, this natural flood control system was obliterated, with excess rainwater having no other recourse but in streets and highways instead. In the city of Manila, particular areas that are always flooded include Tondo, Sampaloc, Quiapo, and Sta. Cruz, all of which were once home to several streams and waterways. Similar things also happened to the tributaries of the Pasig River. For instance, the Pateros River, which branches from the Marikina River, was encroached by so much human structures that it became so narrow that it looked like a constricted canal. In the case of the Marikina River, poor urban drainage systems, heavy siltation from creeks and canals emptying into the river, as well as tons of uncollected garbage, hampered the river’s natural flow.
Lastly, many parts of Metro Manila are also below sea level, such as Malabon City. Unlike the Netherlands, which is also below sea level but is protected by huge dikes, the metropolis’ low-lying areas have no physical buffer against flooding. Compound that with a burgeoning population squeezed into already densely-populated areas and you’ve got a recipe for disaster when the rains come.