Flood + Forest: A Migration Corridor ForReconnecting the Brussels Landscape

by  Wim  Wambecq  &  Bruno  De  Meulder

Published in Scenario 06: MigrationSummer 2017

Brussels’ ecology and urbanity

Belgium’s topography, formed during the “tertiary” pre-ice age, slopes down fromSouth to North, towards the coast. However, Belgium’s main natural systems are East-West oriented, following the gradient of eolian deposits from the Quaternary Period:heavy sand soils wouldn’t travel as far as the lighter loamy soils when blown inlandfrom the sea [1]. The map of Potential Natural Vegetation below shows the cleardemarcation of zones of plant communities [2]. In reality, these zones are expressed asa continuous gradient, following the equally soft gradient of soil types. Similarly, forestplants distribute in a mosaic of communities corresponding to vegetation zones, soilconditions, and topography.

The main rivers crossing the Brussels Metropolis – the Dyle, the Senne, and the Dender– run along the tertiary topography perpendicularly across the landscapes thatnaturally develop under the soil gradient. These river systems are consideredfundamental in connecting different communities and habitats. In the face of climatechange and temperature rise, they will only gain importance as corridors for themigration of species that are in search for new habitats where they can survive,following their ideal climatic condition northwards [3].

Figure 1. The zonal Potential Natural Vegetation maps illustrate the distribution ofplants species in and around Belgium, illustrating the geological sequence of east-west

oriented ecological entities and the alluvial river valleys crossing. Legend left: 1-2Coastal-polder system (dune and alluvial forest); 3 Tidal river landscape; 4 Poor Oak-

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Beech forest; 4bis Poor sand, heathland, and coniferous forest; 5 Rich Oak-Beechforest; 6 Beech forest; 7 Winter oak and birch forest; 8 summer and winter oak forest.

The Brussels Metropolis lies squarely in the way of the Senne River Corridor. Bymarginalizing the main water course, the metropolis blocks migration of plants, fish,amphibians, birds, insects and other, in favor of urban movement [4]. Urbaninfrastructure has manipulated the landscape up to a critical point. In other words, theBrussels metropolis jeopardizes the possibility for nature to adapt to climate change [5].

Figure 2. The Potential Natural Vegetation in and around Belgium more closely to animage of reality: a continuous forest with gradually changing forest plant

communities.

Brussels was founded between the forested plateau of loamy soils in the East and thewet, productive alluvial plain of the Senne to the West. The Quaternary deposits on thesteep slopes in between, eroded over time allowing the sandy “Brusselian” tertiary layerto outcrop and create a system of sandy slopes. These slopes mark the transitionbetween the upper and lower city. In the city center, they formed iconic spaces: theNational Administrative Center, “Mont des Arts,” the justice palace, and “sablon,” nowone of the most prominent public spaces in Brussels whose name refers directly to theexploitation of (slightly clayish) sand. In the South, the forested sandy slopes of ForêtDrogenbos were amongst the most attractive spaces for housing due to their greensetting and often-spectacular panoramas over the Senne Valley [6].

Today Brussels has overpowered its geological base. Anthropogenic interventionsdominate development logic. This is most apparent in Anderlecht-Drogenbos, wherethe project discussed here is located [7]. The area is highly fragmented by the large-scale city infrastructures that cross the southern Senne Valley: the canal, the railways,the Brussels ring way and their industrial offspring. Each of these pieces ofinfrastructure changed the topography of the valley, leaving natural flows largelyinterrupted or crippled [8].

Figure 3. The four sites that formed the subject of research-by-design, commissionedby the Brussels Capital Region and the Flanders region, including Brussels city center.

Figure 4. Gradual fragmentation of the Senne valley south of Brussels over time.

The cultural landscape impacts the “continuum natural,” or ecological structure, in itslithological, geomorphological, hydrological and even atmospheric constitution andthus jeopardize the possibility for the Senne valley to serve as a migration corridor forall sorts of species [9]. The cultural colonization of the landscape was neveraccompanied with any concept on how this ecological continuum might be safeguardedor compensated, or what Ian McHarg stated applies well to this case: “This growth, wehave seen, is totally unresponsive to natural processes and their values” [10].

The vocation of the Southern Senne Valley: Brussels’ major flood plain

The Anderlecht Drogenbos site, located south of Brussels and known as the “SouthernSenne Valley,” holds a unique ecological and urbanistic position. Here, on the transitionbetween middle-high and low Belgium, the river valley widens, before bottleneckinginto the Brussels’ urban tissue. What if we can regain a momentum to establish an

ecological corridor for migration by giving the site a main metropolitan vocation: here,the millions of liters of water entering and threatening the city could be halted andstored in an enormous floodplain, effectively ending Brussels flooding problems.

Figure 5. The main topography in the transition from middle-high to low Belgium:Brussels lies squarely on the Senne River. Site four of the research-by-design is

strategically located upstream and shows a wide valley, opening possibilities forstoring water.

The re-establishment of nature as driver does not attempt to romantically turn backtime. Instead, it embraces, even relies upon cultural interventions—the highway dyke,Catala industrial compound, the industrial islands in the valley—as an addition to thegeological base, or what is now called the “Anthropocene” [11]. If applied correctly, anew urban ecology can appear that builds on a superposition of layers of infrastructuralintervention, such as the canal, railway, and highway, just as ecological communitiesbuild upon geological strata. The multiplication of dams will allow huge amounts ofwater to be stored temporarily, while simultaneously creating a continuous ecosystemof wetlands, flood plains and dry forested areas along the Senne River. Solving the city’sflood problem is the perfect alibi to redesign the natural landscape with its piecemealcultural interventions into a migration corridor with a high diversity of habitats.

Figure 6. A system of dams creates a reoccurring system of wet to dry landscapes thatform interconnected stepping-stones for a high level of biodiversity.

Reconstructing Ecology: soil, water, and forest

To understand the biodiversity of ecosystems, it is necessary to appreciate the centralorganizing role played by a dynamically varying physical environment [12]. Landscapedynamics shape the urban environment. Urban development typically leads to thereduction of dynamic change and flexibility since these properties introduceuncertainty into an otherwise ordered and engineered system. In this way, peak waterflow is calculated and “safely” guided towards a piped system; trees are removed sincethey might fall or their roots might lift sidewalks; unstable soil is fixed by mineralizededges to prevent potential erosion. Many of these securities are only temporarysolutions or limited in their effectiveness. They are mere illusions of safety.

Soil, water, and vegetation are determining aspects of ecosystems [13]. Themanipulation of soil alone has the potential to reconfigure the Southern Senne Valley.Through cut and fill operations, preferably with a zero soil balance, water can beredirected, halted or redistributed. Water must be allowed to return to the site and “actnaturally,” which means developments can no longer simply guide it towards the safestlinear system, the most direct route off of a site, but instead contemplate where watercan be, permanently or temporarily, tolerated [14]. The movement of soil and re-

naturalization of water creates continuous dynamic gradients of wet to dry and clay tosandy soils. On this rich base, vegetation communities, mostly composed of diverseforests, can reclaim their place. By piecemeal operations, the valley can be shaped intoan ecological corridor.

Figure 7. Gradually building habitats: cut and fill operations over time allow forwater scraping, which in turn leads to the establishment of forest and the habitat.

Figure 8. Targeted, easily feasible interventions in time condition the flood plaintowards a future “natural” state. The engineered landscape becomes dynamic and

resilient.

The river alluvial soils are composed of a range of unique geological formationsresulting from different cycles of eolian, riverine, glacial and coastal deposits and bycultural adaptations. The alluvial plains can be in some locations dense and continuous,in others locally extremely heterogeneous. Together, they compose Belgium’s variedecological entities. This diversity comes from natural elements of Belgium’s landscape,but it can also be more intentionally activated for the purpose of ecological continuity,corridor function and the system of stepping-stones that emerge from the soilbiodiversity.

Flood + forest urbanism: new urban realm

Floods and forests shape the territory. Floods define “no-go” places for urbandevelopment. Forests instead can accommodate the urban. What if we accept thatforests are a necessity for the functioning of migration corridors, and for a strongecological community? We would be forced to imagine an urban realm that develops atthe grace of the forest, much like Brussels initially developed at the grace of the SonianForest.

Forests that develop in the wet, frequently inundated lands of the alluvial plain aredense and difficult to penetrate. These closed forests only allow for urban settlement attheir edges or in a clearing. Forests on sandy soil that are less fertile develop a moreopen forest structure. Instead of carving out clearings in the forest, urban developmentcan nestle inside its open matrix. In between clearings and nestling inside a range ofurban-forest conditions [15]. If the forest represents the architecture of ecology, thenwe should find an urbanity that fits this architecture.

Figure 9. Flood (Water – W), Forest (F) mediate a new migration corridor from thehinterland (H) into the city (C). A range of urban figures appears that fit into the

ecological conditions of the migration corridor.

Figure 10. Enlarged plan of intervention, the ecology of the Senne Valley pushesthrough the urban tissue, conquering space for an ecological continuum however

possible: from large (forested) floodplains to a system of smaller linear corridors. Theurban system adapts to and benefits from these new landscape conditions.

A pebble in the valley

The project site in the industrial area of Catala, a former paper factory up forredevelopment, sits squarely on the Senne River. If the narrow passages of the Sennearound the industrial platform are conditioned to allow only a certain amount of waterto pass through, a vast floodplain emerges that can store up to one million cubic metersof water that otherwise would have to be flushed through the Brussels piping and canalsystem.

The industrial site is like a large pebble in the water. A dense, partially productive,partially residential program could be welcomed here. Surely this unique location as apebble in the water, and a clearing in the dense alluvial forest would be the pretext for adifferent urban lifestyle. One could understand the disruption the clearing means in theecological system, and simultaneously understand that it is exactly this pebble thatmakes the ecological corridor function at the scale of the metropolis.

Water and forest: the metabolism of the city

On the border between the Brussels-Capital Region and Flanders, the valley has beeninvaded and encroached on by a lot of “peripheral” industrial functions, which havebeen pushed away from the city center. Most of them use water for industrial processes:the energy plant uses water for cooling, the chemical plant uses it in their productionprocesses. Here the Senne is seen as part of an industrial network, which is easilyconsidered damaging, problematic or incompatible with a sustainable water ecology.

What if we embrace these operational aspects of the river and incorporate them withinan ecological system, rather than considering them off-limits? By closing the watercycle for each of these processes and making the different water functions of theindustries work together, a new habitat can be created that finds its origins in theindustrial processes. This habitat is not fragile and does not survive “despite” theindustrial processes, but “at their grace.” In turn, the landscape can even take up a rolein the industrial process (e.g. in contributing to decreasing water temperature or aidingin water purification processes).

The privatized nature of industry would allow the ecological corridor to remain largelyuntouched. Here, the alluvial forests would not be publicly accessible since they are partof the operational frame of the industries and must to be protected. Nature can thrive.Sporadic “machines,” part of the industrial operations that organize the waterexchanges, would be tolerated in this landscape since they strengthen the function ofthe water landscape.

Figure 11. Urban metabolism: different flows join through a Combined Heat andPower plant that uses waste as a resource. Urban functions support pioneer

vegetation in the valley.

An industrial urban forest

The industrial islands in the alluvial plain in Anderlecht are synonymous withecological disaster. Flooding is frequent, hence the safe islands and the relativetemperature is higher than elsewhere in Brussels due to the extent of paving and theurban heat island effect. What if we radically overthrow the notion of the “island”? Canthe island be synonymous for the ecological transformation into a piece of the SenneValley migration corridor?

Here, the components of the island are exploited: the sandy plateau allows for an openforest to absorb the industrial buildings and to introduce infiltration andevapotranspiration to combat the temperature problems. The island serves as amanagement system to rationalize the use of space. The internal mineral circulation isgiven up for afforestation, yet space for intensified industrial activities can be found.

Finally, the island no longer represents a safe distance from the alluvial plain. Theisland is an integral part of the ecological system, containing gradients from dry to wet,from sand to clay to loam. The Senne River will be allowed to meander through theislands and thus permeate the industrial tissue as a network of narrow ecologicalconnections. If the connections are not generous in size, at least there are many.

The island approach allows for growth and development over time. Island by island,zones can transform at their own pace. At the speed of a growing tree, the urban forestemerges.

Figure 12. Weaving the urban forest through the industrial islands by inverting spacemanagement from individual to collective.

Forest intimacy and panoramic views

The eastern slope of Brussels forms an iconic edge between the valley and the forestedplateau. In the city center, the slope is accentuated by a system of iconic places. In thesouth, the slope should represent a different urban and ecological approach. Theextension of a tram line along the edge, to fill in the mobility gap between tram andtrain, is evident. Could this tram extension break from the “business as usual, transit-oriented densification”?

The tram extends towards Beersel Castle, serving as the destination of a voyage throughthe forests of the eastern slope. Much like the Tervuren tram connection, the use ofpublic transport is more than a functional habit. The voyage is an alternatingexperience of the open panoramas on the Senne Valley and the closed intimacy of theslope’s forests. A democratization of this quality should exist, and densification of thetram line can be done punctually. The future research question is then clear: whatwould an urban form look like that embraces this view and the intimacy, withoutcompromising this experience from the tram?

Figure 13. New dams hold the water. The gradient of landscapes from bottom to topillustrates the rich and continuous biodiversity created close to the city, ideal for the

migration of species. The urban overlooks the floodplain. A new scenic and functionaltramway traverse the forested flanks of the migration corridor.

Conclusion

The project illustrates the intention to restore ecological continuity through three mainsteps: first, a clear vocation was given to the migration corridor: the major flood plain ofBrussels. This mentally prepares the site for a major transformation, gathering thedifferent stakeholders needed to realize such an ambition. Secondly, the classic conceptof “city building” is overthrown. We should no longer add to the urban proliferation ofintervention with a sole purpose of urban evolution. Each cultural intervention, bydifferent stakeholders or in different moments in time, should contribute toestablishing the “continuum natural,” or ecosystem. Natural and cultural forces shouldbe synchronized to accommodate natural processes. Finally, the urban realm is in needof a paradigm shift. Housing development should be embedded in the new ecologicalstructure, not deny it, nor ignore it, but actively search for it and exploit its manyopportunities. An urban realm that forms a critical part of the ecosystem is more likelyto support and defend it. The notion of “forest urbanism,” an urbanism that fits inside avariety of forest types, and is capable of inhabiting, not erasing the diversity of localvegetation communities of Belgium, could be valuable to explore in support of thesenew ways of living.

Credits

This project was developed within the framework of “Metropolitan Landscapes,” aresearch-by-design study commissioned by the Brussels Capital Region and theFlanders region in 2015 to investigate the role of open space in the Brussels Metropolis.The author of this project is WIT Architects with the Research group for Urbanism andArchitecture (RUA) of KU Leuven in collaboration with Annabelle Blin and PhilipStessens. Figures 9 and 10 represents the further development of the project design byJoris Moonen (WIT and RUA) and Wim Wambecq (RUA) that is currently displayed at

the Vlaams Bouwmeester office in Brussels.

Wim Wambecq (1984) is an architect (2007), and urbandesigner (2009) graduated from the universities KULeuven,IUAVenetië, TUDelft, and UPCBarcelona. After a few years inthe practice of urbanism and architecture at Brussels andMilan-based Italian office Studio Associatio Bernardo Secchi –Paola Viganò, he is currently working on a doctoraldissertation that investigates the interplay between urbanismand forestry in the nebulous Flemish city. Except for European

Urbanism, he is also active in design studios on landscape urbanism in East and SouthAfrican development contexts.

Bruno De Meulder (1960) studied architecture at theUniversity of KULeuven where he also developed a doctoraldissertation on urbanism in the Belgian Congo. Currently, heteaches urbanism at the KULeuven where he is director of thepost-graduate programs of human settlements and urbanism.In his research theory and practice, analysis and design,history and contemporary urban practices cross.

Notes

[1] Michael Borremans, Geologie van Vlaanderen (Gent: Academia Press, 2015).

[2] The forest plant community that would naturally settle and thrive under the dynamics of natural processes if nottaking into account the notion of time, as proposed by Tüxen in 1956.

J. Cornelis, Martin Hermy, B. Roelandt, L.De Keersmaeker, and Kris Vandekerkhove, Bosplantengemeenschappenin Vlaanderen: een typologie van bossen gebaseerd op de kruidlaag, (Brussel: Agentschap voor Natuur en Bos,2009).

[3] Sebastiaan Van der Veken, “Range dynamics of forest plant species in the face of climate change,” (Leuven:K.U.Leuven Faculteit Bio-ingenieurswetenschappen, 2008).

[4] Many species would benefit from the proposed project, amongst which some of the “most wanted” species on theBrussels wish list: the iris, Iris pseudacorus, symbol of the Brussels Capital-Region, the Salamandra salamandra(“Fire Salamander”), the hawk, the peregrine or also the Garden Dormouse (Eliomys quercinus) that is on the IUCNRed List of Threatened Species, would benefit from a landscape that not only find continuity along the river, butequally on the slopes and the plateau through continuous forests and bocage landscape. Also, day butterflies arestrongly affected and might make a spectacular uprise if it can reclaim its habitat of humid forests, forest edges oropen forests.

Rapport over de staat van de natuur in het Brussels hoofdstedelijk gewest Jaarverslag (Brussels: LeefmilieuBrussels, 2012).

[5] R. Hamdi, O. Giot, R. De Troch, A. Deckmyn, and P. Termonia, “Future climate of Brussels and Paris for the2050s under the A1B scenario,” Urban Climate 12 (2015): 160-182.

[6] H. Meert, De aardrijkskunde: driemaandelijks tijdschrift van de Vereniging leraars aardrijkskunde 13 (1989):277-304.

[7] This was the study area of the project within the frame of Metropolitan Landscapes. The site starts more or lesssouth of the Brussels pentagon.

[8] Joris Moonen, Wim Wambecq, Philip Stessens, Annabelle Blin, Guido Geenen, and Bruno De Meulder,“Metropolitan Landscapes. Ontwerpend onderzoek in en rond de zuidelijke Zennevallei” (Leuven: KU LeuvenOnderzoeksgroep Stedenbouw en Architectuur, 2015).

[9] Manuela Raposo Magalhães, M. Abreu, M. Lousã, N. Cortez, Estrutura ecológica da paisagem: conceitos edelimitação-escalas regional e municipal (Lisboa: ISA Press, 2007).

[10] Ian McHarg, Design with Nature (New York: John Wiley and Sons, 1992), 57..

[11] Sverre Raffnsøe, Philosophy of the Anthropocene: The Human Turn (London: Palgrave Macmillian UK, 2016).

[12] N. LeRoy Poff, J. David Allan, Mark B. Bain, James R. Karr, Karen L. Prestegaard, Brian D. Richter, Richard E.Sparks, and Julie C. Stromberg, “The natural flow regime,” BioScience 47(11) (1997): 769-784.

[13] Eugene P. Odum, Fundamental of Ecology, (Philadelphia: Saunders College Publishing, 1971), 211.

[14] McHarg, Design with Nature, 56.

[15] This spatial aspect of the forest is called the “light climate,” with four main categories: dense forest with largeclearing and white light; a dense forest with a small clearing and reddish light; an open forest with blue-greyish light;and closed forest with yellow-greenish light.

Jan Den Ouden, Bart Muys, G. M. J. Mohren, and Kris Verheyen, “Bosecologie en bosbeheer.” (Leuven: Acco, 2011).

Cite

Wim Wambecq and Bruno De Meulder, “Flood + Forest: A Migration Corridor for Reconnecting the BrusselsLandscape,” Scenario Journal 06: Migration, Summer 2017, https://scenariojournal.com/article/flood-forest/.

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