De Slagen pumping station stimulates nature development in Natura-2000 area West Langstraat

To stimulate nature development in the protected Natura 2000 area Westelijke Langstraat, a range of measures is being taken in and around Waalwijk to adjust the direction of water flow and raise the water level in the nature area between Waalwijk and Waspik. The most prominent part of the Adjusting Water Management Waalwijk project is the construction of the brand new main pumping station in the Zuiderkanaal canal. De Slagen pumping station is the result of intensive cooperation between the Brabantse Delta Water Board, Dura Vermeer and GMB.

Commissioned by the Brabantse Delta water board, GMB is designing and realizing all five pumping stations and several weirs, while Dura Vermeer is responsible for environmental management, earthwork and site design. "On paper, Dura Vermeer is our client and main contractor for the project, but in practice we are working together intensively as full partners from the start," says GMB project manager Michiel van Ierssel. Iwan Netten of Dura Vermeer can agree and adds: "In that sense, it is a unique partnership. We also work jointly from a single project location in Waalwijk." 

Golden combination

Van Ierssel: "This is a Design & Construct contract. For the main pumping station, we drew up an integral 3D model based on a preliminary design in which all disciplines and interfaces were worked out: civil/construction, mechanical and electrical engineering. The 3D model was also effectively used for early coordination with the water board administrator in the design phase regarding the accessibility and maintainability of the pumping station." Netten continued: "The pumping station will be built in an earth dam where a sheet pile structure has been created as a replacement dam. Because of the weak subsoil encountered, we first had to pre-load the soil dam for four months and GMB changed the foundation design to a pile foundation. Dura Vermeer's expertise in geotechnical engineering combined with GMB's multidisciplinary knowledge and experience with polder pumping stations proved to be a golden combination here. It led to several optimizations."

Pressure pipes follow dike profile

Pumping Station De Slagen has one superstructure structurally, but functionally consists of two separate pumping stations with capacities of 10,800 and 4,320 m3 per hour. That's the equivalent of six Olympic swimming pools per hour. "Each pumping station has two fish-friendly pumps that pump the polder water from the Zuiderkanaal and the Capelsche Polder via 2×2 pressure lines several hundred meters away over a dike to the Bergsche Maas outflow structure," Van Ierssel explains. "Initially, a 9-meter-deep valve well in the dike was part of the design. Working closely with our partner Royal HaskoningDHV, we optimized the hydraulic design so that the discharge pipes now follow the profile of the dike. This creates a form of siphoning action in the pressure pipes and the deep well has been eliminated. For all parties a considerable improvement in terms of safety, (execution) risks, accessibility and maintainability in the user phase."

The design, execution method, planning and phasing are completely intertwined on this project, according to Van Ierssel. "We continuously tested the design for manufacturability. For example, in an early phase of the design, the construction pit of the pumping station was changed to a wet pit with underwater concrete. In this way, we preventively eliminated a significant risk of damage to the environment due to drainage. Nice to experience within the team the integral, constructive cooperation between the disciplines, designers and work planners/executives and crucial for a successful project. By using a Lean methodology, we get to the bottom of the work and create maximum involvement of all parties. Moreover, this saves us time. The De Slagen pumping station will be completed in the summer of 2022. Then the water system will be ready for the future and nature can continue to develop in the Western Langstraat."