Evaluation of slopes delivery to catchment sediment budget for a low‐energy water system: a case study from the lingèvres catchment (normandy, western france)

Abstract

Quantification and characterization of hydrological and sedimentary transfers are now major challenges to preserving uropean soils and water resources (aw on ater, ater ramework irective). In northwestern rance, stream water quality is currently reduced by suspended sediment. However, in these low‐energy water systems, sediment origin and dynamics into the catchment remain difficult to analyze from a local to a regional scale because of intermediary traps caused by landscape structure (hedgerow areas) and land use organization on the slopes. To provide a better understanding of sediment dynamics in these systems we proposed to analyze runoff dynamics on slopes and to assess slopes' contribution to the sediment budget of a catchment. This study is based on sediment connectivity analysis, used to accurately determine runoff dynamics between producing areas and the outlet of the catchment. This work is focused on the Lingèvres catchment (15 km²), a typical feature of the low‐energy water system located in the western part of rance, in between open‐field and bocage landscapes. The results demonstrate that in a hedgerow landscape, known for its protective role against runoff connection to the river, sediment delivery from slopes is more important and efficient than in an open‐field area where no obstacles are observed. This is explained by diverse drainage densities and spatial organization of roads, and ditch and plot entries which induced differentiated sediment delivery from agricultural plots and the river. However, they also underlined the weakness of sediment delivery from slopes compared with sediment fluxes exported from the catchment. Conversely, they highlight the fundamental role of erosion processes due to agricultural practices and landscape organization in headwater systems, which seem to be the main functional area at the sub‐catchment scale.

Key words:

• slope erosion
• sediment connectivity
• sediment yield
• headwater systems
• drainage density

Additional information

Notes on contributors

Vincent Viel

Vincent Viel, Université Paris 7 – Diderot, UFR G.H.S.S., Site Olympe de Gouges, 5 rue Thomas Mann, 75-013 Paris, France

E‐mail: [email protected]

Daniel Delahaye

Daniel Delahaye, Romain Reulier, Laboratoire LETG‐Caen GEOPHEN, UMR 6554 CNRS, Université de Caen Basse‐Normandie, Esplanade de la Paix, 14-032 Caen Cedex, France

E‐mail: [email protected]; [email protected]