The Parisian urban region is currently experiencing Europe’s largest urban transition centered around a 200 km mobility network (the Grand Paris Express) and intended to project the city beyond its historic boundaries and into the 21st century. This inevitable urban restructuring is reconfiguration spatial, socio-political, and cultural relations between the urban center and the periphery but is also considerably affecting the ecological functioning of the larger riverine territory of the Seine Basin from which it depends on. This thesis investigates the ecological, geological, and hydrological consequences of material extraction needed to construct the Parisian Urban Project, looking most notably at sand and aggregate quarries used in the production of concrete. While this graduation project does not look to offer an alternative to extractivism, it looks at applying a material practice of repair on damaged landscapes to mend for past destructive actions and reintegrate post-extraction sites into a larger production system. This project first constitutes a joint narrative between the urban project of the Grand Paris and the territorial project of the Seine watershed. This relational outlook is intended to form nonlinear and dynamic links between the urban and the territorial, land and water, and culture and matter to uncover the uneven and exploitative practices occurring in and around the river system. This project then follows urban matter - materials associated with the construction of the urban - through a forensic exploration, associating socio-cultural crisis with political and economic agendas and their physical manifestation beyond the conventional urban boundaries, looking at cultural and physical forces applied on geologies and the processes of de/re-territorialization of matter. Finally, this thesis formulates a territorial vision embedding a new material cycle in the Seine River Basin and proposing a design intervention towards repair in La Bassée, the last remaining upstream wetland in the watershed. This vision provides a dual social and ecological rehabilitation of post-extraction sites towards an integrated multi-species riverine landscape adapted to the instabilities of the New Climatic Regime.