A Glimpse of Flood and Sediment Disasters

Issues Confronting Metro Manila Flood Management

2011-08-16T05:41:00.000-07:00

Is there a solution to Metro Manila's perennial flood? Despite the multi-billion investments poured to Metro-Manila, flood is not totally eradicated or confined. And it will not be.

Flood results from the topographical, hydrological social, political, and the available infrastructure conditions in the basin. The magnitude and severity, measured in depth, duration and extent, varies accordingly.

Hydrology

PAGASA has four types of climate according to Corona classification . Based on this, Metro Manila belongs to I, two pronounced seasons, dray from November to April, and wet during the rest of the year. Maximum rain period is from June to September. Maximum annual rainfall is approximately 2000 mm in the flat region and 3000 in the mountainous Sierra Madre mountains.

Topography

There are four river basins traversing the metropolis: Tullahan River Basin in the northern part, San Juan River Basin and the Pasig-Marikina River Basin in the central part, and the Laguna Lake Basin influencing the eastern part.

The Pasig-Marikina River emanates from the Siera Madre mountains. It traverses Montalban, San Mateo, Marikina, Pasig, Mandaluyong, Manila down to the mouth. Montalban and San Mateo has gentler river slope, while Marikina has mild to gentle slope where meandering is observed. Central Metro Manila lies in an alluvial flat. It is relatively low, with waterways influenced by tidal fluctuations.

Western and Northern Metro-Manila is flat and influenced by tidal fluctuations. Flat and tidal influenced terrain usually has low energy head or velocity necessitating pumps for the drainage system to flow smoothly to the rivers under natural condition.

Tullahan River catches the discharge from La Mesa Dam and tributaries from Bulacan. It finally flows to Valenzuela, and Malabon. Malabon lies in the Delta, which make it swampy and influenced by tidal fluctuations.

Laguna Lake Basin receives inflows from 24 rivers from Laguna, Cavite, Batangas, Rizal, and Metro-Manila. It serves as a temporary retarding pond from the floodwaters from Marikina River. Slow drain of the lake is attributed to one outlet, the Napindan Channel.

River Characteristics

River reaches are zoned into segments: M, 1, 2 and 3. M is for mountainous areas characterized by steep slope, high velocity, and predominantly with rocky banks and river beds. Segment 1 is alluvial fan, with few bends and meanders. Imagine the inverted ice cream cone. As the water reaches this section, the water explodes into cone shape manner. River lines are multistrands or meandering. Segment 2 is where narrow plane and natural levees are formed; heavy meandering is expected due to slow down of flow allowing the sediments to settle or be carried away. Hence, river course is highly dynamic as shifting is influenced by sediment transport and deposition. Saltating riverbed materials are carried and deposited alternately to form an irregular alignment. Segment 3 is delta, influenced by the flow from the river upstream and surges due to tide fluctuations. Water is brackish conducive for mangrove, where bio-diversity is very rich. (Unluckily, in urban areas, these are turned to ports). The flow rate is relative to tide fluctuations. Large and small meandering is expected (as in the case of Navotas, Malabaon).

Infrastructure

Pumps to diffuse the flood waters to rivers are aging and surpassing its efficient years. On the other hand, drainage systems were designed decades back with short term foresight with two to ten year probability period. As a result, the drainage systems are outdated and insufficient to accommodate the present dense environment and erratic climatic highs.

Social Impacts on the Topography, Geology and River Dynamics

As population grows, build up sprawls like a wave from the river mouth to the fringes of hills and mountains. Banks, bridges, foot of the mountains sprout with colony of informal settlers, land development, commercial establishments, public and private buildings, etc. Natural water detentions, streams, and natural outlets are diminishing and the land covers transform to paved or impervious materials. Run-off becomes fast and flash floods devastate residential, commercial, agricultural and other areas.

Indiscriminate dumping to the waterways plus the uncollected garbage which goes along with the runoff further disrupt the flow. Exacerbating the situations are the encroachment of buildings and structures erected illegally and made legally. Upstream development triggers soil erosion. Water flows with floating and suspended sediment and garbage load inevitably clog the waterways.

On the other hand, land subsidence is reported by UP NIGS in the Central, Northwest, and Southwest Metro-Manila, which is attributed to water extraction and soil compaction pressed down slowly by built up of residential and high rise establishment over some decades. Navotas, Malabon, Valenzuela, and Kalookan (known as KAMANAVA) swampy areas have been residential, fishing and docking areas.

As the rain begins to fall from the sky, some particles are caught by the leaves for a time until the rain drops accumulate and trickles to the twigs, then branches, and further to the ground. The water enters the spaces of the soil and infiltrates beneath until it reaches the root system of the tree, where the root takes the necessary amount of water and hold the moist and wet soil.

Trees are canopies which delay the raindrops to reach the ground, and the roots and the soil they hold are small natural reservoirs for a definite time. Although during prolonged rainfall the the roots can not guarantee the stability of the steep slopes to prevent the collapse, in general, trees retard the surface runoff.

Structural Proposals to Mitigate Floods

Spillway

After Ondoy, some said the old master plan of Metro-Manila, which was formulated during Marcos era, must be reviewed. One of the major proposals was to build the Parañaque Spillway to hasten the subsidence of high water stage in Laguna Lake via canal with a maximum capacity of 350 m3/sec from the lake to Manila Bay. High water in Laguna lake affects the lakeshore communities in Eastern Metro Manila, Rizal and Laguna; likewise, the discharge from rivers, especially the Marikina-Pasig River and tributaries. The energy of the flow is diminished greatly as the lake and river waters converge. Overflow is experienced in the unprotected and low lying banks.

The spillway was a hot item then. It was heralded by a leading and prominent urban planner over media, both print and broadcast. However, as time ticks it becomes less and less feasible and outdated. Environmental considerations include the built-up areas which would be traversed by the channel and the possible salt water intrusion. In hydraulic point of view, the elevation of the Laguna Lake and the Manila Bay has a slight difference (say 3 meters under high lake stage and 0.5 meter during dry season and in consideration of the high tides). Therefore, it is not economically and technically sound. Even if a superpump is installed to gain energy head, the cost of operating and maintaining one, plus the efficient years of use, can not add up to its feasibility.

Underground Tunnel

Another structures hoped to be installed is an underground tunnel, ala smart tunnel in Kuala Lumpur. The shield machine to build the tunnel is not available and very expensive to acquire from Japan or Europe. Again, consider the flat terrain and differences in gradient in flow dynamics. It requires pump again to speed up the flow. Also, the garbage thrown and deposited on the waterways will clog the tunnel. Operation and maintenance become steeply affordable.

Laguna Lake RingDike

Ring dike around Laguna Lake is another possibility. Ring dike will also serve as road which will hasten transportation around Rizal and Laguna and neighboring cities and provinces. Existing dike completed under JICA funds was the North Lakeshore Dike (now a part of the proposed C-6 project). Taguig, Pateros, portion of Pasig City and Taytay are partially protected by the structures. It is equipped with four pumping stations.

However, completing the dike around the lake will require land acquisition incurring monumental cost on the part of the government before the actual equally expensive dike is built.

Retarding Basin

Retarding Basin is one of the feasible options at present to reduce the impact of flood to Marikina-Pasig River. Retarding basin is a temporary storage from the discharge from the main river course to reduce the steepness of the peak discharge via diverting portion of flow to the the pond. Storage capacity depends on the volume the retarding basin can accommodate flood waters; hence, there is limitation for a prolonged rainfall lasting more than the time the basin can accommodate.

Proposed spots for retarding basins are in San Mateo and upstream of Tumana Bridge in Marikina City.

Rainwater Harvesting

Rainwater harvesting is a technology that captures precipitation for domestic or other purposes. Small scale storage that will last for a week or so is the drums or other small containers directly attached to downspout or conduits from the rooftops. Collectively, the household rainwater harvesting may retard the flood peak relatively low.

Larger scale decreases the steepness of the hydrograph or delays the peak discharge during flood time. Under this category is retarding pond, basins, or depression storage. In Japan, retarding ponds are used as multipurpose arena for recreation or sports, such as football fields.

Policies

The water code stipulates that the Secretary of Department of Public Works and Highways can declare a flood control zones. On the other hand, the Local Government Code allows the Local Government Units to make land use plans and build infrastructures within their jurisdictions.

Still Under Construction

Flood Control Papers

2010-11-07T18:42:00.000-08:00

Ondoy: After A Year

2010-09-11T06:01:00.000-07:00

The tragedy unforgettably left emotional scars to Metro Manila residents. People were surprised, unsuspecting and unprepared for a 6 hour torrential rainfall which inundated the whole Metro Manila. Love ones, properties, livelihood, opportunities were gone. Trauma pervades those who were severely affected. Some were displaced permanently, especially those who are under makeshift roofs.

Pasig-Marikina River, Mangahan Floodway and Laguna Lake are silted. There is no solution yet to underprivileged bank dwellers, who were blamed as one of the reasons for extensive flood, as they block the free flow of flood waters. Marikina City Government continues to decorate barges as passageway across the river as part of their beautification program for their river park. There is no dredging in the upper Marikina River to increase the capacity. Structural interventions are not yet in place. EFCOS which failed to deliver valuable information during the calamity is now eyed by different agencies, offering bright schemes and innovations to revive or overhaul the whole system. (What a way to impress). Even the academe may be tapped to draw out their long stocked modeling software to forecast the behavior of the flood. La Niña is gaining strength expected to peak in the last quarter of the year while experienced meteorologists left and were sacked. Meanwhile ordinary people are still complacent after so many months of no flood days.

Still vulnerability is high for the residents of Metro-Manila. There are still big uncertainties. Preparations are sufficiently far behind for calamity with intensity as Ondoy. We hope it will not come so soon.

As vulnerable people, with little or no defense, there is only One Place where we can take refuge. When we acknowledge our weaknesses that is the time we spend time on our knees and seek protection and provision from Someone greater and powerful than us. The government is not powerful enough, even my neighbors, and city mayors, and barangay officials. There is only one greater and more powerful above all, the creator of universe and the controller of nature. God. Do you trust Him?

EFCOS Deteriorates

2009-10-25T17:58:00.000-07:00

On 26 September 2009, Typhoon Ondoy (International name Ketsana), which brought 341 mm rainfall for six hours or 455 mm for 24 hours surpassing the montlhy average for September (Science Garden station), flooded the cities of Marikina, Pasig, and the towns of Cainta and Taytay in Rizal. Marikna River overflowed and the Laguna Lake swelled with bigger aerial inundation as the water level reached 14 m. People were displaced approximately 2.3 M and claimed around 341 lives. Damages were estimated at PhP4.79 Million in infrastructure.

EFCOS was put into spotlight because it was not operational at the time of calamity where EFCOS was believed to alleviate the disaster's impact through real time hydrological and meteorolgical information. If relayed properly to affected municipalities on time, preparation and evacuation of the people in flood risk area could be done.

The MMDA priority seemed to rely, at the least, on non-structural approach; hence, little attention was given to maintenance of the facilities. It was killed softly with time without any intention of resuscitating reasoning that the facilities are out modeled and ready for phase out.

In EFCOS Phase I - completed in 1993 - PCs microprocessor was 486 with DOS and Windows 3 operating system; data entry was with Lotus 123 encoded manually and simulated through the Japanese model Storage Function Model. In the second phase 2001, some electronics spare parts were replaced with new smaller chips. The PCs were Pentium III with Windows 98 or 2000 and XP. The data were interfaced automatically with the system; hence, data entry was minimized. Simulation and forecasting was easier with MIKE 11 overlaid on GIS platform showing the inundated areas according to the water level. However, DHI MIKE 11 was not sustained since the interfacing with the system encountered glitz and nobody has technical capability to mend. People from Danish Hydraulic Institute could easily do the repair; however, since it is not the priority of the MMDA, the computer model was shelved.

Now, the Microprocessor is QuadCore which enable fast and reliable computing. Even without the expensive MIKE 11, HEC-GEORAS and RAS, free software from the US Army, the hydrological and hydraulic simulation can be done with same results.

Technological advances may out model the existing system but the latest technology becomes cheaper, more reliable and readily available. Upgrading the old chips, the panel boards, the computers and software would not entail as high as PhP 500 Million, I supposed. Locally manufactured and innovated telecommunication equipment can replace the imported Japanese hardware. If reasoning is EFCOS is now obsolete, then PLDT, Smart, Globe, and other telecommunication companies would not thrive in competition by depending passively with their hardware. Looking at the trends and the available viable technology and applied science would enhance the preparation, resilience, evacuation and in general our strategy to cope with the disaster.

The justification purported by the management for not keeping and sustaining the system was that it was outmodeled and would cost P500,000 per station and its present worth due to deterioration is now equivalent to a cell phone. However, the system would not decay at its present condition today if the management regarded its significance on the onset that the facilities were turned over to them. Since then, purchase of spare parts or other alternative replacement was set aside as EFCOS was an additional budgetary burden in their allocation and there were more important items to put money into until Ondoy occurred. It was a big blunder to give an armored vehicle to a school boy. Simply, the system was handed wrongfully to an agency which does not maximize EFCOS.

Weeek Long Decision

2008-08-23T23:23:00.000-07:00

Agonizing moment pondering on what is life ahead of Vientiane consumed much of the last week of January 2008. it was debilitating emotionally and physically. Uncertainties and away from the family and home flooded my mind.

Information of Vientiane from the internet is not even favorable as Laos is a communist country banning tacitly Christianity. Reports on US websites recount incidences of persecutions and hostile apprehensions.

The workplace at FCSEC, my office, was a comfort zone. Rooted for almost seven years with familiarity and honed skills made the office atmosphere enjoyable. It was difficult to leave and give up. But the salary was low to sustain the family needs and pay the debt.

I decided to fly 05 February 2008 where I could go as early as 28 January 2008 to spend sometime with my family.

An offer putting my stability in Question!!!

2008-01-17T00:48:00.000-08:00

Counting the financial requirements for the coming months, I can not imagine how we can manage with our expenses; debt to pay, tuition fees and school services; food and other necessities, etc. It is tempting to grab the offer of higher wages away from the family, which is a very sad predicament.

Working abroad with triple wage compared to the amount I am receiving now will be a relief to financial burden. It is indeed a difficult thing because the time for the family is curtailed. The idea of raising the kids with them troubles me a lot. There is a price to pay.

I am reminded of Isaiah 31:1, " Woe to those who go down to Egypt for help, who rely on horses, who trust in the multitude of their chariots and in the great strength of their horsemen, but do not look to the Holy One of Israel, or seek help from the LORD."

Doing Good Without String Attached!!!

2007-08-20T05:45:00.000-07:00

Looking back, past mentors' influenced in ones life are treasured possessions. Guiding with love and encouragement enables the person to stand on his feet even though there are times of waggling.

Their unwavering support as they look at me sailing independently as I traveled the life's journey reminds me of the need for other people regardless of their strengths and weaknesses.

Renewed Commitment!!!

2007-08-18T00:29:00.000-07:00

It's funny thing how for so many years, I've kept my commitment but drifts through as time passes by. Well, listening to old messages reminds me of the priorities that should be on top, not immersing myself in trivial things that may side track who I really am, my make-up and my personal identity.

Although now, I seldom meet my mentors, the wonder of web enables me to discover the messages heard long time ago, say 25 years ago. The messages remain true even through the ages.

His Promise

2006-03-08T19:50:00.000-08:00

Come to Me, all you who are weary and burdened, and I will give you rest. Take My yoke upon you and learn from Me, because I am gentle and humble in heart, and you will find rest for your souls. For My yoke is easy and My burden is light."