The Seine Basin is a vast territory stretching from Burgundy to Normandy, encompassing more than 18 million inhabitants. The multiple tributaries of the Seine form a spectacular array that traverses, irrigates, and connects rural areas, metropolises, valleys, and plains. This is the result of nature's slow work over centuries, shaping the landscapes of our daily lives.

The Seine Basin is a living environment for humans as well as other animals and plants, hosting a diversity of life. Its benefits for ecological and evolutionary processes are a resource to protect and adapt human societies in the face of global changes.

This territory is significantly influenced by human activity: the forest density is low while agricultural activity and urbanization are heavily present around the major waterways. The Seine estuary receives the discharges of 30% of the French population (18.3 million inhabitants), 40% of national industry, and diffuse pollution from 25% of national agriculture (1). Climate change leads to both water scarcity (the average flow of rivers is gradually decreasing, and agricultural needs have increased) and an increase in extreme phenomena (floods, droughts). In response to these challenges, rainwater infiltration and more responsible consumption are key to creating more resilient societies and territories.

As part of the 43rd session of the International Urban Planning Workshops, the Ateliers de Cergy propose to place water at the heart of territories. How can our territories ensure the long-term preservation, accessibility, and quality of water in the Seine watershed and its tributaries? How does our relationship with water reconfigure our territories and lifestyles to address the major challenges of this century, at both the Seine and local scales? What renewed relationship can be established between the river, its tributaries, and our human activities (energy, food, mobility, leisure, etc.)?

The Ateliers thus invite the territories of the Seine Basin and various water stakeholders to join this reflection, culminating in an international urban planning workshop. Twenty young professionals and students from around the world will work in teams for 20 days in September 2025 to collaboratively and creatively propose bold ideas to outline a grand "Seine Garden."

(1): Data from the Agence Seine Eau Normandie