Nature Based Solutions from practitioners’ perspective: a paradigm shift. The example of bioengineering techniques for riverbank erosion control in urban context: « We work with the living » A management paradigm shift in practitioners’ perspective on riverbank soil bioengineering

International audienceSoil bioengineering are construction techniques based on living vegetation, frquently used for riverbank stabilization to control erosion (Bonin et al. 2013). Compared with civil engineering (e.g. riprap)structures based on, soil bioengineering offers many advantages such as cost reduction, limited impact on environment and production of ecosystem services (Evette and Frossard 2009). Such techniques are typical of Nature Based Solutions (NbS), as they promise to reduce water related-risk, conserve biodiversity, and cope with climate change (Cohen-Schacham et al. 2016).The NbS concept has quickly found success in the academic field and on political agendas (Cousins 2021). However, a knowledge gap still exists on the issues of NbS implementation and the “territorialization" process , with a lack of knowledge in stakeholder involvement and motivations.In this paper, we explore the practitioners’ perspective, by exploring the following question: “to what extend NbS requires a shift in management paradigm?” Our conceptual framework is based on the concept of management paradigm, ie as a way to define a problem, to make a diagnostic and to propose an action (Halbe, Adamowski, and Pahl-Wostl 2015; El-Zein and Hedemann 2016).We focus on soil bioengineering techniques for riverbank protection in urban context, with several case studies from the Rhone Alpes basin (France). We interviewed 17 practitioners : scientific institutes, local authorities, design offices, and construction companies. We analysed these semi-structured interviews with qualitative methods (Olivier de Sardan 2004). Our results reveal that switching from civil engineering to soil bioengineering is not only a technical change, but also requires a paradigm shift. First, soil bioengineering techniques lead to redefine the performance of engineering structures, by widening the perspective of performance assessment and including new performance criteria such as ecological performance or landscape integration. Second, bioengineering techniques question the risk acceptance and risk sharing between practitioners. At last, bioengineering requires a posture change, with new soft skills (humility, ability to question, daring) and a new collective organization (collective feedback, peer-to-peer exchanges) . Finally, such techniques implies a shift from a “predict and control” paradigm to an “adaptive management” paradigm.Our contribution addresses both the question of operationalizing NbS in urban areas and the role of management paradigm in every-day engineering practices