Wallaard builds underground basin in Alphen aan den Rijn |
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Aarplein gets smart water buffer: prevents flooding and nourishes greenery
Aarplein in Alphen aan den Rijn is undergoing a major transformation. In the heart of the redeveloped city centre, not only are a modern shopping centre and new housing being built, but underground, smart water management solutions are also being implemented. Contractor Wallaard is responsible for the redevelopment of the square and is finalising the construction of an underground retention basin.
| Video still (render) from the animation of the entire process by Jaap Appel (Wallaard's D&C advisor) |
Beneath Aarplein, a concrete water buffer has been constructed that collects rainwater during wet periods and uses it to irrigate trees and plants during dry spells. The basin is 6 metres deep and measures 20 by 8 metres, providing space for approximately 500 cubic metres, or 500,000 litres of water. The water is discharged into the soil via an infiltration well at a depth of 30 metres. In case of heavy rainfall, excess water is released into surface water systems.
Water glass seals the soil
To build the basin, the existing paving was removed and steel sheet piles were installed to define the excavation area. Since the subsoil mainly consists of sand, Wallaard was able to inject water glass into the ground. This created a watertight seal, allowing the sand to be quickly excavated. Wellpoint dewatering ensured that groundwater was drained during the work. "Everything is going according to plan, and the weather is on our side — a textbook project," says site manager Johan Bronkhorst.
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"With these kinds of constructions, safety, quality and efficiency always come together"
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Solid concrete structure supports traffic
After the excavation, the basin floor was poured first, followed by the walls. In total, 300 cubic metres of concrete and 70,000 kilos of rebar were used. The walls are 35 centimetres thick. Next came the concrete roof with access hatches, designed to support traffic on the square. "With these kinds of constructions, safety, quality and efficiency always come together," says senior site manager and concrete specialist Vincent de Vries.
Square redevelopment in full swing
Now that the underground work is complete, Wallaard is starting on the visible part of the redevelopment. "New sewers and house connections are being installed, street lighting is going up, and underground waste containers are being placed. After that come paving, street furniture and signage. Since the work is taking place in a busy area, access to homes and businesses is always maintained," Wallaard notes.
The municipality of Alphen aan den Rijn aims to turn Aarplein into a lively, green square, with space for shops, hospitality, greenery and bicycle parking. The work is expected to be completed in September 2025.
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The rainwater collected by the water buffer during wet periods is used to irrigate trees and plants in dry times.
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 | | Video still from the animation by Jaap Appel (Wallaard's D&C advisor) |
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This article was previously published on 18 June 2025 on the website of Stad + Groen.
| Gemeente Alphen aan den R... | |
| Wallaard Groenvoorziening | |
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