An overview with engineer Vanessa Villeneuve and architects Frank Wallenborn and Beate Heigel.
Building a new urban site on the industrial wasteland of Belval required major reorganisation of water management, which had to be not least rethought in the light of sustainable development criteria. From the integration of existing piping into a new urban planning concept to the structuring of an innovative rainwater retention system and wastewater management, the task was colossal… and very challenging for the AGORA team. An overview with engineer Vanessa Villeneuve and architects Frank Wallenborn and Beate Heigel.
What were the main challenges for water management at the very beginning of the Belval adventure?
Vanessa Villeneuve: “In the beginning, it was an abandoned industrial site with a ghostly appearance. There was already piping and on this we had to put a concept of urban planning and develop it while considering the existing networks. There was also the river network, the historical stream, the Wenschelbach, which had been channelled for the needs of the factory operation. It has been diverted, partially reopened and renatured: it has been one of Belval’s great challenges to bring value to this stream. In general, our task was to start from an existing and complex hydrological situation, to graft a new urban plan onto it, to make sure that it works with the natural environment and to deal with pollution issues. It was also necessary to respect the history of this territory: to echo the natural watercourse and the uses of water in the former industrial context.”
Frank Wallenborn: “Initially, the Belval rainwater retention concept was a requirement of the Luxembourg legislation, which the Belval site wanted to comply with even before the law was published. The first thoughts on this subject date back to 2002.
Upcoming and current legislation requires retention capacities within each PAP (Special Development Plan).
However, the transposition of this requirement to each of the fifteen or so PAPs, intended to cover the Belval development, seemed neither feasible from a technical point of view, nor satisfactory from the point of view of landscape integration.
It was decided at the time to establish a water management concept for Belval, taking into account the imperatives of water retention, but also the desire to integrate the necessary retention capacities into a coherent landscape concept, covering several PAPs. The solution adopted was to centralise the retention surfaces in landscape elements common to the PAPs at strategic locations (the Waassertrap) and to create additional capacity in existing structures such as the Arbed ponds. In this way, the flow of water into the stream has been regulated and the stream is not overloaded downstream.
From this global concept, we tried to build a common urban plan: not only did we want to build retentions, but also to marry them with beautiful landscaping. This concept was born 20 years ago, and was an avant-garde project at the time. Today it is still to be considered as a pioneer project in this area in the Grand Duchy.”
What makes the Waassertrap, or water staircase, a unique and avant-garde concept?
F.W.: It is truly one of Belval’s great features! It is designed to collect up to 6,300 m³ of rainwater through 24 retention steps. Each step contributes to the gradually slowing down and controlled discharge of the significant precipitation volume. It is a centralised retention system that collects water from Belval North, Belval South, part of the Square Mile and Um Belval Park. From all these areas, a large part of the rainwater flows through both open and underground networks to the Waassertrap. Engineering is thus combined with a unique and very original landscape concept. When it’s not raining, the steps are available to city dwellers and blend into the natural landscape. They are also part of our compensatory measures of the biotope plan: they have specific vegetation and constitute a living environment, with a fine diversity of species.”
V.V.: “Specifically wood was used for the construction of the steps, which act as barriers. We had to remain within an ecological framework, to work on precise engineering to move towards making the best use of the water so that there is no waste. It is a really interesting project, and 100% embedded in an ecological and sustainable development vision.”
Was the Waassertrap also imagined as an aesthetic project, creating beauty in the park and in the city?
Beate Heigel: “Absolutely. This was achieved, for example, by taking into account that rainwater retention in the park will not be a permanent requirement – our design leaves these areas free for other uses during the rest of the time and integrates harmoniously with the landscape and green spaces. Retention ponds, as often seen near highways or supermarkets, are created as purely functional structures. Since they are not used for part of the year, they sit there like gaping holes, looking like concrete structures, surrounded by fences and unattractive. And there is nothing like that in Belval. In the immediate vicinity of the Waassertrap, the Belval South Park, also designed with an open rainwater drainage system, completes the scheme and connects to it.
What were the challenges in wastewater management?
V.V: “The wastewater from the site to be converted was discharged into the Wenschelbach and underwent treatment in the ARBED lagoons. We immediately wanted to separate wastewater from rainwater to create two independent systems. The new wastewater system would send the water directly to the Esch-Schifflange wastewater treatment plant for effective treatment. The Schifflange plant was being modernised at the time in order to have the capacity to receive, among other water, all the wastewater from Belval depending on its future development.”
In Belval, water was the central element of a happy marriage between engineering, landscaping, ecology and leisure. A positive contribution of water, in an unconventional urban development.
Interviews with Agora employees, partners and experts, with the ” Défis urbains ” series discover the values promoted and developed by AGORA.
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