Water retention under highways
Traditionally, highway drainage systems are designed to remove water as quickly as possible. However, in light of climate adaptation goals, it is more desirable for rainwater to infiltrate the ground where it falls and, when possible, to retain it for longer periods. An innovative system leverages the subsurface to achieve this goal.
This concept has been successfully tested under high-traffic conditions at the InnovA58 testbed operated by Rijkswaterstaat along the A58 motorway near Eindhoven.
As a key player in Dutch infrastructure construction and maintenance, Rijkswaterstaat is committed to making a significant impact. The agency aims to achieve full climate neutrality and circularity by 2030. To accomplish this, Rijkswaterstaat collaborates with market parties, local authorities, and research institutions.
'InnovA58 focuses on testing and accelerating sustainable innovations,' says Wies Vonck, project leader at InnovA58 on behalf of Rijkswaterstaat. 'Initially, we focused on hard infrastructure, testing innovations in asphalt, road markings, and street furniture. Later, we broadened our scope to include biodiversity and climate adaptation. Capturing and potentially reusing highway runoff water has become an important theme.'
Close to the surface
Over the past 2 years, Gebr. Van Kessel has implemented and tested eight different innovations within the InnovA58 testbed, including capturing water directly beneath the highway. 'AquaBASE is a foundation material that captures water under the road at a high level,' says Ignas Ubbink, project and test coordinator at InnovA58 on behalf of Gebr. Van Kessel. This refers not only to high-quality performance, but also to the relatively shallow depth at which water is stored, close to the surface level.
'Unlike infiltration crates or pipes, which penetrate much deeper into the ground and offer limited reuse possibilities, AquaBASE captures, purifies, and distributes highway runoff water via gravity. This can direct the water to a drainage system or even a nearby building for use as flushing water.'
Supported by bacteria
While this concept has been applied in urban and residential areas, it had never been tested on heavily trafficked highways.
'The water retention solution is fundamentally a two-layer foundation system: 30 centimetres of drain mix for water retention, topped with hydromix or mixed granulate,' explains Sander Apeldoorn, AquaBASE business manager. 'Both materials are secondary raw materials derived from bottom ash, a by-product of waste incineration, which is processed into usable material. This makes the solution not only innovative but also sustainable.'
To enhance functionality, geotextile that captures oils has been integrated into the system. Over time, bacteria colonise the geotextile, accelerating the breakdown of oil residues. 'The system can be adjusted for local needs, offering options for water retention, rapid infiltration, or even complete water tightness for reuse,' adds Apeldoorn.
Test sections
The InnovA58 testbed near Eindhoven included 2 different test sections: 1 with drain mix combined with a traditional mixed granulate foundation, and another featuring a hydromix top layer. An additional section was installed to test the effects of water retention within the drain mix. 'When fully saturated, the particle tension may decrease, potentially causing rutting. To examine this, we enclosed 1 section to allow controlled water saturation during testing,' says Ubbink.
Minimal rutting
After 2 years of testing and alternating traffic loads on the test sections, the results are highly satisfactory. 'The raw data is being converted into final conclusions, but visual inspections already indicate excellent performance,' confirms Ubbink.
'A measured rut depth of 3 millimetres is mainly attributable to asphalt settling after placement, which is common. AquaBASE, even with a hydromix top layer, meets the design life expectations of a traditional foundation system. Maintenance is also straightforward: drains and catch basins are easy to inspect and clean, and hollow spaces retain their capacity well over time.'
Climate-resilient infrastructure
For Rijkswaterstaat, the test has been a success. 'Traditional solutions aim to quickly remove highway runoff. This system retains water for longer without impacting road users,' says Vonck. 'We continuously seek innovative ways to integrate highways as part of the surrounding environment rather than viewing them solely as mobility infrastructure. This system makes a vital contribution to restoring water balance in specific areas.'
Source article: COB