When assessing the extent of anthropogenic river transformations, many geohistorical studies focus solely on the main channel at the expense of the floodplain. In addition, the quantification of river planform changes often derives from the superposition of maps, regardless of the information provided by the written record. To address these issues, this contribution presents the geohistorical research conducted on the Bassée alluvial plain in the Seine River valley (France). Located upstream of Paris, this geomorphic entity results from the conjunction of biophysical and human factors over time. Although not “natural” nor “undisturbed”, the early-19th century river and its floodplain still had features of a functional system, with frequent flooding, wetlands, and space for geomorphic processes to occur. However, from the 1850s onwards, land reclamation policies, river engineering and gravel extraction have deeply modified the Seine and its floodplain. While the Bassée has been studied for more than 20 years by the PIREN-Seine program, no research had been conducted on the impacts of hydraulic works on the floodplain. Using both a quantitative and qualitative approach, we show how past developments have disrupted flow patterns and disconnected the Seine River from its floodplain. A classic diachronic analysis was conducted with a geographic information system and the building of transition matrices. We interpreted changes in agricultural land use as environmental proxies revealing more or less wet conditions in the plain. Historical documents reveal that these transformations are linked to various scales of decision, from the local landowner to the State, with conflicts arising between and within each level. Although the trajectory of the Bassée is similar to that of other floodplains in France and Europe, we support the idea that its particular legacies must be considered to define sustainable water resource management goals.

Mathilde Resch (1) and Laurence Lestel (2)
(1) ARCEAU Île-de-France (2) Sorbonne Université-CNRS-EPHE, UMR 7619 METIS

 
ID Abstract: 677