Hydropower is often described as a cornerstone of the global energy transition because of its ability to provide reliable, cost-efficient power and flexibility to balance variable sources such as solar and wind. But these advantages are accompanied by an irreversible consequence: trapping of sediment in reservoirs.

To tackle this challenge, researchers from the National University of Singapore (NUS) have developed a new planning framework that couples river sediment modeling with energy system analysis.

Led by Assistant Professor He Xiaogang from the Department of Civil and Environmental Engineering, College of Design and Engineering, NUS, the team’s integrated water-sediment-energy planning framework enables decision-makers to test how different combinations of hydropower, solar, wind and energy storage affect both energy system costs and sediment delivery.

It provides a transferable, evidence-based approach to chart clean energy transitions that meet climate goals while safeguarding natural ecosystems and livelihoods.

The framework is published in the paper “Strategising renewable energy transitions to preserve sediment transport integrity” in Nature Sustainability.

Striking a balance

Hydropower plays a central and complementary role in the global shift to clean energy. Reliable, flexible and cost-competitive, it supplies about 14% of global electricity and generates more than a third of the world’s renewable power in 2023. However, hydropower dams also block the natural flow of sediment downstream. Crucially, this sediment acts as the building material for river deltas, the nutrient base for agriculture and a natural buffer against coastal erosion.

Nowhere is this tension clearer than in the Mekong River Basin, where hydropower projects are expanding rapidly. If fully developed, large dams could reduce the sediment reaching the Mekong Delta by around 75%.

Home to millions of people and widely regarded as the “rice bowl” of the region, the delta depends on this steady supply of sediment. Without it, farmland would shrink, rice yields would decline and coasts would erode faster.

To study this trade-off, the researchers developed a new framework that links hydrological and sediment-routing models with an energy system planning model. This allowed them to capture the two-way interactions between dam building and sediment delivery, alongside electricity costs and transmission needs.

They applied the framework across 16 scenarios, varying climate policy targets and levels of regional power sharing, to identify strategies that balance renewable energy expansion with ecosystem protection.

However, not all dams are created equal—and not all produce the same impact. Through modeling hydropower development project by project, the researchers identified two broad categories: those with relatively low effects on sediment supply (referred to in the study as ‘low-impact’ dams), and those with disproportionately high impacts (“high-impact” dams). The study found that prioritizing low-impact dams could significantly limit sediment loss while still delivering system-wide energy cost savings.

“River sediment, mostly sand, silt and clay, is not something that can be immediately replaced once it is lost,” said Asst Prof He.

“The way rivers function is influenced by how much sediment they transport and where it is deposited. It underpins the long-term stability of deltas and coasts. Our study shows that strategic optimization can help minimize the impacts of energy transitions on this natural foundation.”

A strategic path forward

The team’s study highlights that a more balanced way forward is feasible. By substituting 19 high-impact dams with alternative renewable sources such as solar and wind, alongside battery storage, up to 98% of the sediment supply to the Mekong Delta could be preserved.

The associated cost increase is modest, with energy system expenses projected to rise by only 4–6% between 2020 and 2050, equivalent to an additional US$15.7–26.0 billion.

Importantly, when taking into account the value of sediment for agriculture and fisheries—estimated at US$12–28 million per megatonne each year—much of this additional cost is offset.

“Sediment is considered non-substitutable, meaning its loss cannot be replaced by other resources,” Asst Prof He added. “Preserving it therefore brings long-term economic and ecological benefits that outweigh the short-term savings from high-impact hydropower.”

The framework also underscores that hydropower development is not an all-or-nothing choice. A portfolio of 34 low-impact dams could still deliver US$19.6 billion in system-wide cost savings while limiting sediment loss to just 2%. This distinction provides decision-makers with a clearer guide—some projects can proceed with relatively milder consequences, while others are best avoided or replaced with other renewables to prevent disproportionate and irreversible ecosystem losses.

Furthermore, the team recommends strengthening regional cooperation in electricity sharing to further ease the trade-offs. Expanded cross-border transmission allows low-impact hydropower and variable renewables to complement one another, reducing costs and improving reliability across the basin.

For instance, the researchers highlighted the importance of building a regional power grid that would make it possible to move electricity more effectively from areas rich in solar or hydropower to centers of high demand, maximizing the value of renewable resources while reducing the need for additional high-impact dams.

Such cooperation could also create opportunities for benefit-sharing mechanisms, ensuring that environmental gains and financial burdens are distributed more equitably. Such mechanisms may include financial compensation, ecosystem service payments or preferential electricity pricing to encourage upstream regions to forgo high-impact hydropower.

“Renewable energy transitions can be designed in ways that serve both climate mitigation and climate adaptation,” said Asst Prof He.

“With careful planning and regional cooperation, it is possible to keep costs low, meet climate targets and preserve the natural systems that millions of people depend on. This approach is not only relevant to the Mekong River Basin, but also transferable to other river basins worldwide.”