The Vlotwatering Bridge is a unique eco-friendly bridge that connects the residents of the Dutch town of Monster with the Poelzone, a recreational area located in the Westland region of South Holland. The 70-meter “Batbridge” was designed by NEXT Architects, a design office based in Amsterdam and Beijing and the construction was finished last October.
The bridge improves the ecological value of its environment by providing an attractive roosting space for the local bat colony, who feed off the river insects. The architects were able to successfully merge the bat’s needs with a curvilinear path conducive for walks and bicycle rides. The serpentine structure is not only functional and aesthetically pleasing but also offers an overlook to the best landscape views.
The project was endorsed by bat expert Marcel Schillemans of the Dutch Mammal Society.
“A textbook example of how a functional object can at the same time serve nature.”
How did the Architects Create the Ideal Habitat for Various bat Species?
The bridge design offers differing habitats aiming to grow a large bat colony around the bridge. Through a well-thought-out design, the structure has three specific bridge components that provide year-round accommodation for bats.
The northern abutment has been designed for winter hibernation. The structural space in the cross section is cleverly used to implement the roosts. The underside of the bridge is provided with entrance slits which are part of a pattern of grooves in the concrete arch. The slits are largely kept out of sight to protect bats from natural predators such as owls. The openings are very small and have a rough finish for grip. They are marked by a series of tinted bricks with open joints on either side. During summer, the bats can stay in the openings underneath the deck and the brick balustrade.
The pedestrian and bicycle-friendly bridge has one side clad in wood and the other in brick. The materials were chosen to echo the materials used elsewhere in the park. The construction consists of 25-meter-long concrete arch spans. The s-shaped deck is supported with a pressure arc that slants under the bridge.
“The Bat bridge is designed to house bats in as many ways as possible. In the design, we figured out that we could use the specific qualities of the mass of the concrete, the height of the construction within the deck, and the railings for pedestrians and bicycles for bats as well. These spaces provide unique opportunities to house bats,“ NEXT Architects explain on their official website.
“One of the noticeable things of the area was that there were already different types of bats flying the route over the water — throughout the winter periods they hide in World War Two concrete bunkers around the area, from the moderate climate. This became our inspiration, we thought we might be able to design the foundation (bridgehead) equating the environmental qualities of a bunker.” explained Bart Reusers, NEXT Architect’s co-founder, to Dezeen magazine.
Bats need different roosting conditions at different times of the year and they will often move around to find a roost that meets their needs.
To optimize the suitability of the bridge for bats, the main structure is made out of concrete. During hibernation, also known as an extended period of deep sleep that allows animals to survive cold winters, bats need cool roosts that remain at a constant temperature. The mass of the concrete provides a stable and pleasant climate both in winter and summer.
For several weeks in summer, female bats gather in warm and dry maternity roosts to have their babies. The walls, decks and concrete foundation were thickened to an average of 0.75m so that the bridge temperature could be relatively stable.
Another Fine Example of an Ecological Bridge
During the design process of the bridge, the architects consulted Herman Limpens from the Netherland’s Mammal Society, one of the leading experts in bat behavior.
“There is no other bridge like it that is specifically designed to house bats,”said Limpens.
Nevertheless, another well-known, bat-friendly bridge is the Ann W. Richards Congress Avenue Bridge in downtown Austin, Texas. The difference between the Congress Avenue bridge and Vlotwatering is that the former’s reconstruction engineers weren’t expecting that new crevices beneath the bridge would make an ideal bat roost.
Today, the Congress Avenue Bridge is home to the world’s largest urban bat colony, with 1.5 million Mexican free-tailed bats emerging from under the bridge, offering a spectacular view to the hundreds of people gathered to witness the bat’s flight. This unusual and fascinating tourist attraction generates ten million dollars in tourism revenue annually.
The architects hope that a large colony of various species will be encouraged to grow around the Vlotwatering bridge, making it a similar eco-tourism destination.
Why Spend Time, Energy and Money on a bat Habitat?
Despite the popularity of the bat bridge in Austin, bats are still among the world’s most endangered and least appreciated animals. Unfortunately, besides suffering from habitat loss and environmental pollution, the primary cause of bats’ decline is persecution from humans. Is it time to give bats a break by not falling for the old myths describing them as scary and dark creatures?
Hopefully, you will even like them a bit by learning about their ecological, economic, and scientific value. For many people, the truth might come as a surprise: bats are gentle and sophisticated animals and bat-watchers have nothing to fear if they don’t try to handle bats. In addition to the economic impact, the Austin bats alone are making the world a better place to live through their nightly eating of 10,000 to 20,000 pounds of insects, including agricultural pests. Bats eating all these insects means fewer chemicals and poisons will be used on crops; equal to a healthier life for all of us.
The Bridge as the Entrance of a Recreational Area
Vlotwateringbrug is part of a greater development project called the Poelzone, an elongated recreational area in the Westland, aiming to transform the surrounding river banks of Gravenzande, Naaldwijk and Monster into a green public zone in which natural and recreational values complement each other, as well as create new habitats for indigenous wildlife. The unique bridge marks the ideal entry for the Poelzone.
The ecological landscape design is led by landscape studio LOLA Architects. The main features of the 21-hectare zone right through the greenhouse-filled Westland in the Netherlands, are an elongated line of ecological banks, a 1.5 km winding bicycle route, 15 plots for new houses and an innovative setup of a 2.2 ha spawn site for fish.
Nature and Functionality
The Vlotwatering bridge breaks the conventional perception of a bridge as a structure that allows people to cross from one side to the other. Not only does it connect pedestrians and bikers of the town to a recreational area, but also offers an ideal habitat for roosting colonies of bats. This is exactly the kind of project that inspires us to follow ecological thinking to make the world a better place. The Batbridge is a great example of how you can enhance the harmonious coexistence of humans and nature.
This feature originally appeared in Landscape Architects.
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