Monday, October 5, 2009

Flooding in Metro Manila: Historical, Natural and Social Factors

. Caption: Map of Metro Manila and Surrounding Areas (Source: )
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"Inspired" by the recent devastating Typhoon 'Ondoy' (international name: Ketsana) that struck the Philippines on 26 September 2009 and brought massive floods in Metro Manila and surrounding provinces, I searched for relevant articles that I can use to do a scientific study of flooding in Metro Manila.

One interesting paper that I found is that of a New Zealand scientist:

Bankoff, Gregg (2003). "Constructing Vulnerability: The Historical, Natural and Social Generation of Flooding in Metropolitan Manila," Disasters, 27(3): 95–109.

I would like to quote some excerpts from his paper:

"Flooding is not a recent hazard in the Philippines but one that has occurred throughout the recorded history of the archipelago. On the one hand, it is related to a wider global ecological crisis to do with climatic change and rising sea levels but on the other hand, it is also the effect of more localised human activities. A whole range of socio-economic factors such as land use practices, living standards and policy responses are increasingly influencing the frequency of natural hazards such as floods and the corresponding occurrence of disasters. In particular, the reason why flooding has come to pose such a pervasive risk to the residents of metropolitan Manila has its basis in a complex mix of inter-relating factors that emphasise how the nature of vulnerability is constructed through the lack of mutuality between environment and human activity over time."

Dr. Bankoff's paper paper examines three aspects of this flooding:

first, the importance of an historical approach in understanding how hazards are generated;

second, the degree of interplay between environment and society in creating risk; and

third, the manner in which vulnerability is a complex construction.

Dr. Bankoff's paper notes that:

"Metro Manila is situated in a semi-alluvial floodplain formed by sediment flow from
the Meycauayan and Malabon-Tullahan river basins in the north and the Marikina river
basin in the east.

It encompasses a land area of 636 square kilometres, measuring about
20 kilometres in length along a north-south axis and stretching more than 22 kilometres
at its widest.

The conurbation is open to Manila Bay on the west and to Laguna de
Bay, a large lake, on the south-east.

As such, the metropolitan area now constitutes a
vast urbanised drainage basin that experiences frequent inundations from overflowing
rivers and storm waters that render the existing system of esteros (modified natural
channels) and canals constructed during the Spanish and American colonial periods

Despite the growing vulnerability of much of the
metropolitan area, however, rapid urbanisation has continued unabated with residential
homes, industries and commercial sites increasingly exposed to flood-related

Dr. Bankoff further elucidates:

Leonardo Liongson and Peter Castro classify flooding in Manila into three
types: local, moderate and regional. Local street flooding is the result of intense,
sudden thunderstorms over a few city blocks that cause inundations of 20–50
centimetres, light property damage and heavy traffic congestion. Typically flooding

happens because curb inlets, drainage culverts or natural upland ditches are insufficient
to handle the sudden volume of water. Such events occur all over the metropolitan area
but are more frequent in low-lying areas. Moderate flooding is produced by intense
rainfall of over an hour’s duration that is often associated with tropical cyclones and
affects a wide area of the city with inundations of more than 30 centimetres. Damage
to property can be considerable; there may be isolated cases of personal injury or even
loss of life; and whole districts become impassable to vehicle movement. Again,
moderate flooding mainly occurs in low-lying areas of the capital. Regional flooding,
on the other hand, affects whole cities and may cover several river basins. It is a largescale
condition consequent upon typhoons that ensues from heavy rainfall lasting over
several days and may be aggravated by high tides or storm surges. All gainful
activities are severely curtailed until the waters subside.
  • While flooding variously affects all areas of Manila, some cities and
    municipalities are more vulnerable than others due to their location and height relative
    to sea level. Some 20 per cent of the capital’s 63,600 square hectares is designated as
    flood prone, of which 5,385 square hectares (41 per cent) are served by pumping
    stations and the remaining 7,715 square hectares (59 per cent) suffer frequent and longlastinginundation.

  • Areas to the east, south-east and south of the
    capital around Marikina, Pasig, Mandaluyong, Muntinlupa and Parañaque and
    especially those adjacent to Laguna de Bay such as Taguig and Pateros are acutely
    susceptible to flooding.

  • In some particularly exposed cities such as
    Muntinlupa and Taguig, all barangays (the basic unit of local government) are
    regularly inundated and the coverage of flooding extends to 88 per cent and 83 per cent
    of their respective land areas.

Below is Dr. Geoff's conclusion:

  • Flooding is not a recent hazard in the Philippines but one that has occurred
    throughout the recorded history of the archipelago: it is the result of the low-lying
    nature of much of the terrain and the frequency of typhoons. These typhoons do not
    necessarily constitute hazards as such and are, in fact, responsible for a significant
    percentage of the annual rainfall that makes the islands so fertile and thus ideal for
    agriculture. This fertility, in turn, encourages or at least permits demographic growth
    and the location of people in large cities such as Metro Manila.

  • The demands of this
    steadily expanding urban population for basic amenities such as water, together with
    the nature of modern development, generate environmental problems like accelerated
    subsidence and garbage disposal that, in conjunction with the torrential rainfall
    associated with tropical storms, aggravates the incidence and severity of flooding in the
    metropolitan area

  • The concentration of employment, educational and health among
    other opportunities in the ‘big city’ only spurs more rural-to-urban migration, creates
    shortages of suitable residential land and encourages the occupation of areas more
    prone to flooding or that have important drainage functions.

  • The actions of governments and the technological solutions they mainly favour have only limited outcomes and may actually aggravate conditions usually to the disadvantage of the
    most vulnerable poor, whether urban or rural. The construction of vulnerability to
    flood in Metro Manila, therefore, clearly shows how societies and destructive agents
    are very much mutually constituted and embedded in natural and social systems as
    unfolding processes over time

In connection with the recent devastation brought by Typhoon Ondoy to the Philippines, in particular to Metro Manila and surrounding provinces, I find the article of Dr. Geoff very enlightening. It explains that vulnerability and "natural" disasters are complex phenomena that should be studied holistically: historical, natural and social factors that shape the floods in Metro Manila should all be considered.

The aftermath of Typhoon 'Ondoy' includes the suffering of thousands of Filipinos who are in need of immediate relief and long term rehabilitation. Although it is heartwarming to note that a lot of Filipinos are helping the typhoon and flood victims through relief efforts and volunteerism (or voluntarism) we, as a nation and a civil society, should should look into the root cause of the problem so that appropriate solutions can be found and applied.

We should not romanticize the situation (as some people are wont to do); instead, we should identify the root cause (or causes), search for long lasting solutions and implement them.

Raffy Saldaña
5 October 2009

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