A new study has looked at historic flooding of the Yangtze River and concluded that human attempts to temper flood risks may have actually made things worse. From ancient dykes to modern dams and floodgates, the team has concluded that, overall, these may have made flood events more devastating.

The core idea is deceptively simple: if you squeeze a river into a narrower space, the same volume of floodwater has fewer places to go. The result is that flood events, when they occur, can be amplified rather than dampened.

Historically, when the Yangtze flooded, water spread into surrounding floodplains, lakes and wetlands. Locally, this was clearly bad news, but those areas acted like enormous temporary storage tanks.

In other words, they absorbed water, slowed it down and released it gradually. In response, people then built embankments, drained lakes and reclaimed floodplains for farming and development. That protected those particular areas from ordinary floods, but the team claims, removed much of the river system’s overflow capacity.

To support their claims, the international team, led by Yu Shiyong of Jiangsu Normal University, looked at flood events over the last 500 years as the core of their study. They combined sediment archives, historical reports, and high-resolution climate reanalysis data to reconstruct the size and scale of historic floods along the river.

Did humans make Yangtze floods worse?

They found that embankment construction increased the estimated magnitude of a 100-year flood by about 18%, while lake enclosure and reclamation increased it by about 8%. A “100-year flood” does not mean one flood every 100 years. It means a flood of that size has historically had roughly a 1% chance in any given year.

But, you may well wonder, aren’t dams and levees supposed to prevent this? In short, they do, for smaller, more frequent flooding events. But the team argues that measures intended to control flooding can amplify the peak discharge of rare, extreme events.

Another problem human measures like dams and levees seem to have created, the team argues, is a perception of safety. With them in place, locals feel more secure in living in flood plains and will build houses, factories, etc, in places where they otherwise wouldn’t.

Termed the “levee effect,” when an extreme flood eventually overtops or exceeds those defences, the resulting damage can be much greater because more people and assets are now exposed.

So what can be done? The team argues that a more hybrid water management system might be better going forward. Rather than removing dams and levees, etc, they argue for strengthening defenses where needed, especially near large population centers.

They also argue that lakes and wetlands should be reconnected to rivers, and floodplains should be restored and preserved to act as natural flood absorbers. The team also suggests setting up controlled areas that can act as artificial floodplains, and restoring forests and wetlands upstream to slow rain runoff into rivers.

Nature knows best

“The core idea is not to eliminate floods, but to allow them to accumulate, divert and be released slowly in a predictable, controllable and minimally damaging space,” Lead author Yu Shiyong said in an interview.

“An ideal flood control system for the Yangtze River should be a robust river and lake ecosystem with self-adjusting capabilities, rather than relying solely on ever-rising dykes,” he added.

“Truly modern water management is about scientifically determining which areas must be protected, which areas should be left flood-prone, and when to store water and release it, while ensuring that the costs and benefits are shared fairly,” Yu added.

You can view the study for yourself in the journal Proceedings of the National Academy of Sciences of the United States of America.

💾

Researchers from the Southwest Research Institute (SwRI) have successfully developed an optimized spark-ignited hydrogen engine suitable for medium-duty commercial vehicles. As a form of internal combustion engine (ICE), the new engine behaves much more like a diesel engine than earlier hydrogen engines.

In other words, it is not a new kind of fuel-cell engine, but rather burns hydrogen inside cylinders using spark ignition. Just like a petrol engine, the new ICE produces mechanical propulsion using pistons.

“In addition to decades of developing medium- and heavy-duty engines, SwRI has some of the most extensive experience in the world developing and testing H₂-ICEs for internal research, clients and industry demonstrations,” said Dr. Qilong Lu, a program manager in SwRI’s Powertrain Systems Engineering Department and one of the leads on this project.

“The engine was designed, constructed and rigorously tested at SwRI to ensure efficiency and performance,” Dr. Lu added.

Diesel-like torque hydrogen engine

“We began at the single-cylinder level, focusing on optimizing combustion and injection strategies,” Lu said. “From there, our team ramped up efforts to develop the full multi-cylinder engine, addressing key challenges such as pre-ignition, combustion stability and overall systems integration,” Lu added.

The attraction is that hydrogen contains no carbon, so burning it produces water rather than carbon dioxide. It also allows manufacturers to retain much of the familiar internal-combustion ecosystem: engines, transmissions, manufacturing equipment, servicing knowledge and supply chains.

The team also managed to deliver the new hydrogen ICE’s diesel-like torque using a turbocharger that forces more air into the engine. This allows it to burn more hydrogen and produce the strong low-speed torque needed to move loaded trucks.

The new engine also has improved airflow thanks to an innovative intake-port geometry allowing hydrogen to burn much faster than petrol and requiring different air movement inside the cylinder.

The engine also features larger intake valves and hydrogen-specific injectors to enable optimum fuel-to-air mixing within the cylinders. It also uses special software and calibrations to precisely manage injection, ignition, boost pressure and the air–fuel mixture.

Another wrinkle they had to overcome is safety. Hot engine surfaces or residual gases can ignite hydrogen before the spark fires, producing knocking, power loss or potentially engine damage.

Low-emissions but not zero

In terms of emissions, the engine produces what the team describes as “near-zero tailpipe CO₂.” While this is true in terms of the engine itself, the way in which the fuel hydrogen is produced matters here.

If produced from natural gas, rather than renewable electricity, CO₂ could remain high, all things considered. Also, hydrogen combustion can still produce nitrogen oxides, or NOx, because combustion heats nitrogen and oxygen from the air to very high temperatures.

It therefore isn’t literally a zero-emission engine and may require careful combustion control and exhaust after-treatment.

“The project brought together many areas and experts at the Institute to complete,” said Chris Bitsis, assistant director of SwRI’s Powertrain Systems Engineering Department, who oversees combustion research programs. “SwRI’s hydrogen combustion engine program is working every day to advance this technology and showcase its potential as a near-zero carbon emissions industry solution,” he added.

💾