Inside the flood walls: How does flood control really work?

The stories of cracked riverbanks, unfinished canals, and dikes that collapse after a single season have dominated headlines in recent weeks. Allegations of ghost projects and kickbacks have hounded the Department of Public Works and Highways (DPWH), raising questions about whether billions of pesos in flood-control funding are truly safeguarding lives — or lining pockets.

To separate the technical from the political, DAILY TRIBUNE sat down with several DPWH engineers. Their identities are withheld to protect them from retaliation. Over coffee, they spoke not of politics but of structures of stones, concrete, and steel — of designs that should stand for decades, but too often fall within years.

The engineers began with canals, the most basic flood-control structures.

“People think it’s just a trench in the ground,” one said. “But a canal is a lifeline. If you leave it as bare earth, it will erode. If you line it with concrete, it resists scouring. If you reinforce it with steel bars, it can withstand higher flows without cracking.”

In low-risk rural areas, earthen canals may suffice. But in towns where floods rush with force, concrete-lined canals — sometimes with rebars hidden beneath — are essential.

“You can tell the difference right away,” the engineer added. “A good lining is smooth, intact, and drains fast. A bad one cracks like old pottery.”

Next came riverbank protection — riprap, rubble masonry, and concrete linings.

“Riprap is just stones piled at the edge,” another engineer explained. “It absorbs energy, but if the stones are too small or not locked, the current sweeps them away. Gabions, wire cages filled with stone are better, but they must be properly anchored with filters beneath.”

Rubble masonry, they said, is often misunderstood.

“It’s stones cemented together with mortar, no rebars. Done right, it lasts. Done wrong, it crumbles. You’ll see mortar flaking after the first flood if the mix was weak.”

And then there is reinforced concrete:

“That’s when you use rebars inside. It’s costly, but for urban riverbanks, it’s non-negotiable. Without steel, it’s like building a house on sand.”

The engineers leaned in when the conversation turned to dikes.

“Earthen dikes are cheapest. You pile soil, compact it, and cover it with grass. But if you don’t protect the toe, water eats it away. If you don’t raise the crest high enough, floods overtop it. Once that happens, it’s game over.”

Rubble masonry dikes, they noted, are sturdier but still limited.

“No rebars — just stone and mortar. They resist erosion, but they can’t fight a raging river without extra protection.”

The strongest, they said, are reinforced concrete dikes with steel bars embedded in the wall.

“That’s where you put money. But they’re expensive, and that’s where corruption lurks — rebars cut short, concrete mixed thin, documents saying ‘reinforced’ but built as plain.”

Every flood-control failure, the engineers said, tells a story.

A dike collapses not just because of rain but because its toe was never keyed deep enough. A canal silts up not because of nature alone but because its slope and lining were poorly designed. A masonry wall cracks not because of time but because the mortar ratio was diluted to save cement bags.

“These are not accidents,” one engineer said. “They are choices.”

Beyond the technicalities, the engineers stressed the human cost.

“A farmer sees water creeping into his field because a dike slumped. A family watches their home drown because the canal overflowed. These are the faces behind every project we sign,” one of them said.

They admitted that many in the field feel powerless.

“We want to speak up, but you know what happens if we do. So we just work, keep the specs as best we can, and hope the next storm won’t expose the shortcuts.”

DAILY TRIBUNE cross-checked their claims with DPWH’s own standards: the Design Guidelines, Criteria and Standards (DGCS), and the Standard Specifications, or Blue Book. These documents require compaction tests for earthworks, bar-bending schedules for reinforced concrete, and manufacturer certificates for gabion wire.

On paper, the safeguards exist. On the ground, however, engineers say enforcement is patchy.

“The documents may be signed, but whether they reflect the actual site is another story,” one said.

As the conversation ended, one engineer folded the sketch on the coffee receipt and slipped it into his pocket.

“We know what right looks like,” he said. “But the public only sees the ribbon-cutting, not the foundation. That’s why media is important, because if no one checks, the wall may be hollow.”