Before We Rebuild, Look Upstream: The Key to Solving the Perennial Flood Problem

The images are now familiar. A bridge disappears beneath a swollen river in Tarlac. Then another bridge is damaged. A vehicle carrying five people plunges into the water with it.

Floodwaters inundate communities in the Philippines, highlighting the need for flood-control planning that considers entire watersheds from upstream to downstream. [Photo: Philippine Coast Guard Facebook]

In Pampanga, dikes give way and communities evacuate. Pangasinan declares a province-wide state of calamity.

Rivers rise in Rizal. Marikina reaches dangerous levels. Streets in Metro Manila disappear beneath brown water. The natural instinct is to look at where the destruction occurred. Perhaps we should also look at where the water began its journey.

Consider Baras, Rizal. Parts of Baras lie within the Upper Marikina River Basin Protected Landscape, a protected watershed extending across portions of Rizal and forming an important component of the wider Marikina River Basin.

That basin ultimately feeds the Marikina River and the Pasig River system downstream.

There is a reason watersheds matter. A healthy upland landscape does not make extreme rainfall disappear. No forest can promise that Metro Manila will never flood.

But vegetation, soil, terrain and natural drainage influence how rainfall is intercepted, absorbed, slowed and released into streams and rivers.

Alter the landscape, and you may alter the way water moves through it.

That is why activities in Baras deserve attention beyond Baras itself. For decades, portions of the Upper Marikina landscape have faced pressures from quarrying, development and other forms of land disturbance.

DENR records have documented mineral agreements affecting roughly 1,343 hectares that overlap protected areas, including portions of the Upper Marikina watershed and areas associated with the Masungi landscape.

Philippine protected-area law now prohibits commercial and large-scale quarrying within protected areas.

This does not prove that quarrying caused this week's floods. Nor should serious journalism make such a leap.

Flooding is rarely produced by a single culprit. Rainfall intensity matters. So does soil saturation, river geometry, urbanization, drainage capacity, dikes, bridges, roads, flood-control structures and sedimentation.

Upstream land-use changes can also influence runoff and the movement of water through a watershed.

With all these factors in play, the proper question therefore is not: Did one quarry cause one flood?

It is: Have we adequately studied how everything we do within a watershed changes the behavior of water downstream?

That question becomes more urgent when we leave Rizal and look north. In Tarlac, two bridges were damaged within roughly a day amid sustained heavy rains and strong river currents.

The collapse of the Agana Bridge sent an SUV carrying five people into the Tarlac River. One occupant was rescued while four were initially reported missing. Tarlac subsequently declared a state of calamity.

In Pampanga, weeks of monsoon rains left the province among the country's hardest hit as of Aug. 31, according to the Office of Civil Defense. Pangasinan, after repeated flooding and damage to agriculture and infrastructure, likewise declared a province-wide state of calamity.

These are not one river system.

Baras does not cause flooding in Tarlac. The Upper Marikina watershed does not drain into Pampanga or Pangasinan.

But they present the country with the same lesson: A flood becomes visible downstream. Its story often begins upstream.

And that should alter the way government thinks.

When a flood occurs, the important questions should include how much water arrived, how rapidly it arrived, whether sedimentation altered the channel, whether upstream land use changed runoff behavior, and whether protecting one community displaced water toward another.

When Metro Manila floods, the immediate priorities are clear: clear drainage systems, operate pumping stations, improve waterways and protect communities.

But the government should also ask what has happened to the mountains, forests, soils and drainage pathways from which some of that water came.

This is why the next great flood-control investment may need to begin not with concrete, but with hydrology. Map the basin.

Reconstruct rainfall patterns over decades. Map historical river courses. Measure infiltration and runoff. Identify erosion and sediment sources. Overlay subdivisions, roads, farms, quarry areas, forests, bridges and flood-control structures.

Then calculate the probabilities on which yesterday's infrastructure was designed and ask whether those structures remain adequate for tomorrow's rainfall. Only after answering those questions should the government decide what to build.

Perhaps a community needs stronger dikes. Another may need river widening. Still another may require dredging or a bridge with a larger hydraulic opening.

Agricultural reservoirs might, where technically and environmentally appropriate, capture some water for later use.

Or perhaps upstream forests need restoration. Perhaps certain activities should simply not occur in portions of a watershed whose hydrological value exceeds the economic value extracted from them.

That last possibility returns us to Baras. When limestone, forest or mountainside is evaluated only by what can be extracted from it, one side of the balance sheet is missing.

What is the value of the landscape while it remains functioning? How much water does it regulate? How much soil does it hold? How much sediment does it prevent from entering waterways? How much biodiversity does it support? How much risk does it help moderate downstream?

Before society decides that a mountain is more valuable broken into pieces, perhaps it should first calculate what that mountain is worth while still doing the work of a mountain.

That is not an argument against all quarrying. It is an argument for knowing where quarrying belongs—and where it does not. The same discipline should govern flood-control spending.

We should stop beginning with a structure and searching afterward for its justification.

Begin with the basin. Understand the water. Compare the alternatives. Calculate the consequences. Then build.

And afterward, measure whether the intervention actually changed the outcome predicted by the study.

This approach will sometimes be inconvenient. A river basin may cross congressional districts. It may cross municipalities and provinces. Its headwaters may lie under one political jurisdiction while the people suffering downstream live under another.

Nature does not care. Nature is organized by watersheds. Government is organized by jurisdictions. Perhaps our flood-control architecture should begin closing the distance between the two.

For when the waters subside in Tarlac, Pampanga, Pangasinan, Rizal and Metro Manila, the government will once again be under pressure to rebuild.

Bridges will be reconstructed. Dikes repaired. Riverbanks reinforced. Billions appropriated.

All may be necessary.

But before another peso of concrete hardens, perhaps somebody should turn the map around.

Follow the river backward. Look toward the tributaries. Look toward the farms, the forests and the mountains. Look toward places such as Baras.

Then ask: Before rebuilding what the water destroyed downstream, have we understood what we are allowing to happen upstream?

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