[2019] DésiVille: Tools to assist in the desilting of artificial soils: methodological developments for the evaluation of desilting potential and a catalog of solutions applicable to cities

The artificialization of urban soils combined with climate change is confronting our cities with various phenomena that are detrimental to the comfort, well-being and, more globally, the health of city dwellers (in terms of urban heat islands (UHI), flood risk, biodiversity and biogeochemistry, etc.). When this artificialization is accompanied by surface sealing, ecological fragmentation is added to the increase in stabilization and compaction of the substrate, the alteration of the urban albedo, the loss of fertility, storage capacity and regeneration of the soil... all nuisances likely to amplify the above-mentioned phenomena.

This sealing, which is generally induced by a change of use of the premises, is not necessarily irreversible. It is legitimate to anticipate, by means of de-sealing, to restore certain natural cycles (water - groundwater recharge, carbon, oxygen, etc.) and to favor the natural regulation of the ambient air temperature in particular. However, this reversibility must not overlook certain side effects related to the rising water table or the sequestration of pollutants such as carbon in the soil and the related risks of resurgence or propagation of pollutants to groundwater.

DésiVille is a 36-month interdisciplinary project that aims to provide an integrated response to the issue of urban soil sealing. Indeed, it is necessary to take into consideration in this dynamic all the "components" of the studied system and more precisely: the uses and choices of redevelopment (social, aesthetic and economic stakes in particular), the atmosphere, the surface coatings, the subsoil and the groundwater, and to model all the flows (energy, water, potential pollutants, etc.) which characterize it before / during / after deseepage The proposal mobilizes different scientific modalities. The articulation will be ensured by means of geoprocessing carried out in a GIS.

The actors of the project are thus committed to developing, in the context of DésiVille: 1) a methodology for evaluating the potentialities and vulnerabilities of the waterproofed interstices of the territory, making it possible to select the most relevant surfaces to be desoiled, 2) a catalog of desoiling solutions integrating, on the basis of the positive and negative impacts identified, a set of recommendations, 3) a test of the method and the catalog within the framework of a redevelopment project for an existing urban area in the Nantes agglomeration.

In order to deal with the transfers on the ground/interface/subsoil, but also with the complexity inherent to the diversity of the scales and phenomena at stake (local climate hazard/UHI phenomenon, soil pollution hazards, flooding by rising water tables, groundwater vulnerability, space amenities, etc.), a multidisciplinary consortium was formed. ), a multidisciplinary consortium has been brought together, associating researchers from BRGM, CEREMA, CNRS and the Nantes School of Architecture, IFSTTAR, and experts in operational urban planning (design office, developer-NMA) in interaction with the local authority (Nantes Métropole). It will benefit from the expertise, data and results acquired in the framework of the European projects Urbinat and Nature4Cities, and the Muse project co-financed by ADEME.
The expected results are manifold: dissemination of scientific knowledge, production of an atlas of potentialities and vulnerabilities (maps and data layers relating in particular to the potential for desilting will be proposed for integration into the Nantes OpenData), a report describing the index of potential for desilting and the evaluation approach, a report grouping together the catalog of solutions, the method of evaluation of combinations at risk and the recommendations approach, etc.