Solving the flooding problem

As a curious teenager, I would often hike to follow a couple of creeks up to their respective sources. This was about 30 years ago and my place in North Caloocan City was a sparsely populated area dominated by rice fields and grasslands.

These sources are actually small, shallow freshwater springs, which I discovered later, feed the creeks and streams that connect to major rivers of Obando in Bulacan and Navotas City.

Sadly, portions of these creeks as well as the springs are now gone, bulldozed to give way to residential projects and public works.

It was then that I noticed the flooding. While not as bad as in some parts of Metro Manila, somehow they demonstrate what happens if natural flow of surface water across the land is not taken into consideration.

Asian phenomenon

According to the World Bank, flooding is the most common of natural disasters and it is increasingly an Asian phenomenon considering that the seven most destructive floods of the past 30 years all occurred in Asia.

In the past 30 years, about 40 percent of flooding worldwide occurred in the continent while more than 90 percent of the global population exposed to flooding lives in Asia.

Based on the guideline titled “Cities and Flooding: A Guide to Integrate Urban Flood Risk Management for the 21st Century,” the most effective way to manage flood risk is to take an integrated approach that combines both structural and non-structural measures. These include building drainage channels and floodways, urban greening such as wetlands and environmental buffers, creating flood-warning systems, and land-use planing for flood avoidance.

Man-made causes

This is because, the most common man-made causes of flooding aside from deforestation are the expansion of farmlands and urban areas—rice paddies, former swamps and other natural waterways were paved over to make way for factories, housing and other services, impeding the natural path of water runoff during the monsoon season.

While trees and other vegetation break the momentum of rain and could help reduce surface erosion, this is not happening in urbanized areas where there is an abundance of impervious cover or hard surfaces that do not allow water to penetrate the soil such as rooftops, driveways and streets.

In urbanized areas, rain pours more quickly off of city and suburban landscapes, which have high levels of impervious cover. In fact, over one-half of all rain becomes surface runoff, and deep infiltration is only a fraction of what it was naturally.

Spillway

In a proposal urban planner Felino Palafox Jr. has been forwarding to every administration since Marcos times, he urged the immediate construction of spillway that cuts through Parañaque City. The Parañaque spillway aims to allow the Laguna de Bay to directly flow to Manila Bay instead of having to pass by the already clogged Pasig River (at 8 km, Parañaque is the narrowest area between Manila Bay and Laguna de Bay).

Members of the Subdivision and Housing Developers Association have also altered the way they plan and develop their projects as SHDA president Paul Tanchi explained they now also include a 50- to 100-year flooding histories of the project area.

“Even the existing developments of our members are being reviewed to check drainage lines if they need clearing and widening,” said Tanchi.

Phinma Properties president and chief executive officer Willie Uy related that more homebuyers are now considering living in vertical developments (condominium) as they offer greater protection against flooding.

Moreover, Uy said, every project they make employs design that is more elevated than the highest recorded water level in the neighboring area.