The river that remembers

After Sendong, can Cagayan de Oro risk hydropower again?

CAGAYAN de Oro has two clocks. One ticks in real time; the other stopped the night of December 16, 2011. 

That was when Sendong (international name: Washi) swelled the river into a wall of brown water that tore through sleeping neighborhoods and left more than a thousand people dead.

Fourteen years later, every heavy rain still sounds like an alarm. 

So when First Gen Corporation announced plans for a 39-megawatt run-of-river hydroelectric plant in Barangay San Isidro, the news landed not as an engineering update but as a memory trigger.

Clean energy is an easy sell. Hydropower is renewable, dispatchable, and free of imported fuel. 

But in a city that once drowned in its own river, “green” is not enough.

The river after Sendong

After the disaster, hydrologist Dominic Tan’s 2019 study Sedimentation Dynamics of the Cagayan de Oro River Catchment described a system still bleeding silt: “A large volume of fine sediment continues to be transported downstream… with deposition occurring in mid-river reaches and near the delta.”

Cabahug and Villanueva, writing in the Mindanao Journal of Science and Technology, found many banks “moderately eroded” and warned that suspended sediment loads during storms could “increase flood stage significantly.” 

In simple terms: the river is heavier, slower, and shallower than before — primed to overflow.

When Espinueva et al. later called Sendong “a flood foretold,” they weren’t being poetic. They meant it literally: upstream deforestation, mining, and siltation had already rewritten the river’s hydraulics long before the storm arrived.

That is the river First Gen wants to tap.

The clean-energy promise

The San Isidro project sits inside a national narrative. Mindanao still suffers rolling brownouts, and the Department of Energy is pushing renewable baseload to stabilize the grid. 

Run-of-river (RoR) hydropower — no big reservoir, just a low diversion weir — sounds like the perfect compromise: smaller footprint, lower emissions, local jobs.

And it’s First Gen, after all: a company that markets itself as the country’s clean-energy pioneer. 

The proposal promises that the river “will continue to flow naturally” and that rafting, a local tourism lifeline, will “coexist” with the plant.

In theory, it’s elegant. In practice, it depends on how the river behaves when the heavens open.

The science says: Smaller isn’t harmless

A 2021 global review led by Arben Kuriqi called run-of-river schemes “less eco-friendly when diversion weirs or pondage structures are employed,” warning that they “may alter the natural flow regime and impair the fluvial ecosystem at different trophic levels.”

In plainer language: even a small barrier can change everything. Flows flatten out, sediments stall, habitats simplify, fish can’t migrate.

A 2023 Scientific Reports study by Ullah et al. found that RoR projects “reduced mean and maximum flows downstream, altered the duration of high- and low-flow periods, and simplified habitat diversity.”

And in 2024, a systematic review by Bipa et al. concluded that hydropeaking — the surge and drop in water release tied to power demand — “affects the downstream ecology regarding fish and benthos habitat” and can intensify erosion.

These are not environmental activist talking points. They are peer-reviewed realities.

So when engineers call San Isidro “low impact,” the real question becomes: low compared to what — and measured by whom?

The city hesitates

In August 2024, Cagayan de Oro’s City Council refused to rubber-stamp the project. The Energy Committee asked for an updated flood model and a comprehensive energy plan before granting an endorsement.

That decision didn’t kill the project. It did something rarer: it introduced humility into development.

Because in a post-Sendong world, every cubic meter of altered flow has moral weight.

What Sendong taught us

If the hydro project moves forward, it must do so under a new social contract — one shaped by science and memory.

1. Prove sediment continuity.

First Gen must show, through independent modeling, that the weir won’t trap the very silt that raises flood levels downstream. Designs should include sluice gates or bypass channels sized for Sendong-scale discharges. Sediment, as river scientists like to say, is the bloodstream of the river. Stop it, and the body swells.

2. Legally bind environmental flows.

No vague “as available” water releases. Minimum flows and ramping rates must be fixed in the environmental compliance certificate. As Kuriqi’s review stresses, “maintaining the natural flow variability is crucial to sustain fluvial ecosystems.”

3. Integrate flood modeling with the city’s defenses.

Hydraulic simulations — using the same HEC-RAS models guiding the JICA-assisted flood-control plan — should test the plant under Sendong-level rainfall. Any predicted rise in flood height, even a few centimeters, in downstream barangays should trigger redesign.

4. Keep the public in the loop.

When spillways open, communities must know instantly. Rafting operators, farmers, and riverside barangays can’t depend on Facebook rumors. They deserve alarms, drills, and direct lines to operators.

5. Audit, adapt, publish.

Real transparency means posting daily flow data and sediment readings online, funding third-party audits after every monsoon, and adjusting operations when the river proves the model wrong.

Why this matters

Mindanao needs power. But it also needs trust — in science, in process, in memory.

Hydropower can be beautiful when done right. It can anchor a circular economy of water and light. Yet in fragile basins like Cagayan de Oro’s, every megawatt must be earned.

If First Gen meets these standards, San Isidro could be a milestone: the first Philippine hydro designed in full daylight, Sendong-proof by design and accountability.

If not, the city will once again pay the deferred costs of progress — in flooded homes and erased barangays.

The river remembers

Rivers don’t forgive; they balance. They carry the evidence of every compromise — tree stumps, gravel, plastic, ash — and return it to us when the clouds decide.

San Isidro’s turbines may someday hum steadily beside the water, a symbol of clean power and corporate pride. But until the river itself is convinced, Cagayan de Oro would do well to listen more than it builds.

Because the river that remembers is also the river that warns.

___________

Sources:

Espinueva et al., A Retrospective on the Devastating Impacts of Tropical Storm Washi (Sendong), International Journal of Disaster Risk Reduction, 2018.

Tan, D.A., Sedimentation Dynamics of the Cagayan de Oro River Catchment, University of Notre Dame, 2019.

Cabahug & Villanueva, Assessment of Soil Erosion, Sediment Transport and Deposition along Cagayan de Oro River, Mindanao Journal of Science and Technology, 2020.

Kuriqi et al., “Ecological impacts of run-of-river hydropower plants,” Renewable and Sustainable Energy Reviews, 2021.

Ullah et al., “Hydrological and ecological impacts of a run-of-river scheme,” Scientific Reports, 2023.

Bipa et al., “Impacts of hydropeaking: A systematic review,” Science of the Total Environment, 2024.