Safe transport of waste water

Riool Zuid carries wastewater from six municipalities below Eindhoven and part of the city itself to the sewage treatment plant, right through the Stratumse Heide nature reserve. The concrete sewer pipe can handle an impressive amount of wastewater: 13,000 m³ of water per hour, or 100,000 full bathtubs per hour on a rainy day. The existing concrete sewer is minimal 1.90 metres wide and 1.50 metres high. ‘You could drive a Mini through it,’ laughs Femke Verhaart of Deltares.

At Deltares, Femke is an expert in hydraulic issues relating to pipe systems, pumping stations and pressurised pipes. She focuses on knowledge issues that will make our wastewater transport future-proof. Beneath our towns and villages lie approximately 126,000 kilometres of pipes, wells and pumps through which wastewater – from toilets, showers, dishwashers and washing machines, but also rainwater – is transported to sewage treatment plants. Femke's expertise has been used, among other things, in the maintenance of Riool Zuid, a project being carried out by water authority De Dommel.

Replacement

The original pipes of this sewer system near Eindhoven were laid five metres underground in 1974 and are in urgent need of replacement. Acids from the wastewater have severely damaged the concrete and, over the years, the sewer has also subsided slightly, causing cracks and creating a risk of leaks or collapses. Maintenance and renewal of three kilometres of sewer is being carried out in phases, so that by early 2026, the waste water can once again flow safely to the treatment plant in Eindhoven.

Testing

In order to replace a severely damaged section of the sewer system, water authority De Dommel installed an emergency pipe above ground, as well as a temporary pumping station, near the Leenderheide junction. ‘The wastewater flows through the pipe to the treatment plant by gravity, but has to be pumped over a small section of a hill by means of the Aalst sewage pumping station,’ says Femke.

To enable the replacement of part of the gravity pipe, the pressurised pipes of the Aalst pumping station have been temporarily extended and a booster pumping station has been installed. Femke: ‘The booster pumps must be designed well such that they could do their job during normal water discharge, but also during extreme water discharge, for example caused by a peak rainfall. In fact, the boosters are essential for draining heavy rainfall in the temporary system. Given the complexity of booster pumping stations, you want to be sure that they work when they are actually needed.’

Confidence

To ensure that the emergency pipeline functioned when needed, water authority De Dommel called in the help of Deltares. De Dommel and Deltares tested the temporary system in practice to see whether it would work when needed. To this end, Femke spent a week in a site hut on the Stratumse Heide, where she simulated all kinds of situations together with the water authority’s engineers, the supplier of the temporary installation and the contractor. This allowed them to test the temporary system, so that they could be confident that it would also work during heavy rainfall.

Femke: "The challenges were that we did not fully understand how the current functioning of the system, the water authority did not want to increase the pressure on the existing 50-year-old pressurised pipes, and a relatively new type of pump was used for the boosters. As a result, the limits of the booster pumps were unclear, while we wanted to test the maximum discharge capacity of the temporary system. So we had to get the most out of the system while minimising the risk of problems. After all, the temporary sewerage system has to function when it rains heavily."

We expect more of these questions in the future. The maintenance task for sewers and other underground infrastructure is becoming larger and more urgent

Femke Verhaart, expert hydraulics at Deltares

Pressure cooker

In the site hut, Deltares, Waterboard De Dommel, Vanderkamp as supplier of the temporary system and contractor Vissers Ploegmakers were able to turn all the knobs to test this. ‘We changed the pressure in the system step by step and regulated the water supply to the system by opening and closing valves, saving a lot of waste water during the night to simulate a rainstorm,’ says Femke. “Every day, we tested the limits of the sewer system. It was quite exciting! All the factors interact with each other, and our system overview is very valuable at such moments. After all, hydraulics does not adhere to project boundaries. We couldn't afford to make any mistakes, because then we would have had to discharge much dirtier wastewater than during a normal rain period into the surface water.”

‘In the end, you learn a lot by hearing the perspectives of the other parties; you have to listen carefully and be able to connect everything. We were all in a pressure cooker,’ Femke recalls. She found the assignment particularly interesting because the impact is immediately clear. ‘As a Deltares expert, you have immediate added value and you can advise your client on the spot and thus help them further.’

Indispensable

“Ultimately, De Dommel asked us to look at both the design of the renovated system and the temporary system from a hydraulic point of view,” says Femke. ‘We expect more of these questions in the future. The maintenance task for sewers and other underground infrastructure is becoming larger and more urgent. Deltares' system overview, our knowledge of pumps and piping systems, detailed hydraulics and our WANDA and FEWS programmes are indispensable in this regard.’

Knowledge community

Femke emphasises the importance of a vital knowledge community for a resilient urban underground infrastructure. ‘In the Capwat community and the Professional Afvalwater Transport knowledge and development programme, among others, knowledge about pumps and piping systems is further developed and transferred, enabling standards and design guidelines to be optimised and allowing you to learn from colleagues elsewhere in the country.’

What will happen if we do not invest in knowledge about our wastewater disposal? Femke: ‘Then the number sewer overflows that end up in nature will increase, with the risk of ecological damage and ultimately also human diseases. In fact, sewers are the best medical invention ever.’