How to protect urban areas from the consequences of climate change?

Pumping stations like La Caldera are becoming increasingly important for urban areas across the globe. That’s because floods like those experienced in Valle de Chalco are on the rise in major cities around the world. According to figures released by the United Nations Office for Disaster Risk Reduction (UNDRR) in 2021, the number of floods worldwide has increased dramatically in recent years – from 1,389 between 1980 and 1999 to 3,254 between 2000 and 2019. According to Rainer Kutzko, Head of Technical Sales Support at KSB in Halle, the demand for KSB’s flood control expertise is growing globally due to heavy rain caused by climate change, the emergence of megacities and increased soil sealing.

In Mexico, for example. After a waste water channel overflowed during a rainstorm in Valle de Chalco in 2010, inundating the neighbourhood with sewage, Mexico’s national water commission CONAGUA took action and drafted an ambitious plan.

The plan was to carry stormwater away from the city via an underground tunnel instead of the overground waste water channel. To ensure that the water in the tunnel drained quickly, the tunnel was to be drilled with a steep gradient to 35 metres below ground level. The pumping station in Valle de Chalco would then collect the water from under the ground and direct it into a channel that would take it out of the valley of Mexico City to where it would no longer pose a threat to residents.

The new pumping station was due to start operation before the beginning of the rainy season in the summer of 2011. The deadline was tight, with just 150 days between placing the order and starting up the pump sets. After all, people’s lives were literally at stake.

Particularly when time is of the essence, meticulous system planning is crucial. As Kutzko points out, “When you are designing a pumping station for flood control, there is no room for error. Everything – from dimensioning to designing the pump inflows – has to be perfect. Otherwise, the system will not provide the protection required in an emergency.”

So, how do you deliver a perfectly functioning system within a tight deadline? The experts at KSB use computer models known as CFD (computational fluid dynamics) simulations to test the flow conditions in different designs in quick succession. This allows them to detect submerged vortices or points at which the water flows so slowly that solids can form deposits that could block the system.

To make the system even safer, the KSB experts also constructed an acrylic glass model of the pump sump, which they could use to test concepts that had been simulated on a computer in real life. By adding dyes to the water at specific points, the experts were able to verify the flows calculated by the computer. To save time, KSB transported the pumps from Halle to Mexico on an Antonov cargo plane.

The intensive preparation that went into designing the system paid off. The president of Mexico, Felipe Calderón, officially opened the pumping station in March 2011, a little over a year after the flooding disaster.

Now, whenever masses of water surge through the underground waste water system towards Valle de Chalco during the rainy season or a rainstorm, the pumps show what they’re made of. “They pump up to 40 cubic metres of water per second from the underground tunnel to the waste water channel above ground level,” explained Kutzko. “I’m pleased to report that the pumps have been running smoothly ever since they went into operation and that there have been no more floods in Valle de Chalco.” 

It is not only countries in monsoon regions that have to worry about the more frequent and more intense flooding caused by extreme rainfall. In late May and early June of 2013, for example, rainfall that lasted for days on end caused rivers to burst their banks in seven European countries. One of the cities hit in Germany was Landshut in Bavaria.

Landshut considered itself well prepared for flooding. The city had built a flood relief channel back in the 1940s and 1950s – a landscaped drainage trough that crosses the city and is used by the city’s residents as a park most of the time. When the water level rises in the Isar river, however, the channel prevents flooding by carrying large volumes of water through the city and back to the river.

The flood that struck in 2013 showed that the system could no longer cope with the changing climatic conditions and that stormwater could not be channelled away fast enough. Because an underground stormwater overflow basin was full to the brim, the water had nowhere to go. Roads were flooded and parts of the industrial area were no longer passable. When Landshut was hit by flooding once again in 2016, the city in Lower Bavaria decided to upgrade its flood control system to be better prepared for extreme weather phenomena in the future.

Landshut is a good example of how an existing flood control system can be adapted to cope with the climatic conditions of the future. The city decided to build a pumping station that would carry water from the stormwater overflow basin to the flood relief channel in the event of flooding.

The engineering consultant for the project turned to KSB to ensure that the station would work perfectly in an emergency. The KSB experts would not only supply the pump sets, but would also lend their expertise to the entire planning process. “Engineering consultants are not usually hydraulics experts,” explained Mehmet Atak, Head of Sales at KSB in Munich.

The municipality of Landshut, the engineering consultant and KSB worked together to design the pumping station. When water flows into the pumping station, it first strikes a curtain wall that reduces its power and velocity. The water is then pumped into the flood relief channel by three high-performance Amacan pumps.

According to Atak, it is crucial to perfectly match the pumps and the structure to each other so that the equipment can operate optimally. “A pumping station is a square chamber into which water shoots under high pressure. All kinds of vortices and air pockets can develop and put added strain on the pumps.” Pumps can become overloaded and switch off as a result. “In that case, you can forget all about the pumping station – you’re going to get flooding,” said Atak.

Across the globe – from Mexico City, New Jersey and London to Landshut, Bavaria – there is growing demand for KSB’s expertise in building pumping stations for flood control. But there is one question that even the KSB experts can’t answer. And that is how much rain municipalities will have to contend with in the future.

“No-one knows what weather conditions will be like in the future. But even if the situation facing municipalities is not yet clear, one thing is abundantly clear: something needs to be done,” said Atak. Although the future is uncertain, he believes that there is room for optimism: “Flooding is a natural event that cities can prepare very well for. And we’re here to help.”