OZCAR-RI OTHU Yzeron experimental catchment - France

The Yzeron catchment (150 km2) is located to the south-west of Lyon city, France. It forms part of the Observatoire de Terrain en Hydrologie Urbaine (OTHU, 2011) long term observatory. It is representative of French periurban areas and is characterised by a marked topography. The outlet reaches the Rhône river at the elevation of 162 meters and the highest point culminates at 917 m above see level. The slope map calculated from a 25 m resolution Digital Elevation Model (DEM), derived from IGN BDTopo® shows that more than 50% of the catchment has slopes larger than 10%. The geology is contrasted with crystalline formations (granite, gneiss ) in the western part of the catchment and more alluvial and glaciar formations in the eastern part. The land use is heterogeneous. The upstream and western part of the basin is limited by a range of hills covered with forests. The intermediate part is mainly covered with grassland and cultivated lands, mixed with urban nucleus. Thin green corridors remain along rivers, covered with deciduous trees. The downstream part is mainly covered with densely urbanized areas. A fast progression of urbanisation is observed since the eighties.
The area is prone to sharp Mediterranean-type flood events due to its steep topography in the upstream part and limited soil water storage capacity overall. The water coming from combined sewer overflow devices is rich of sediments and pollutions, causing quality problems in the rivers, especially during summer storms, where most of the water reaching the river comes from urbanised areas via SODs. Increased erosion of the river banks has also been evidenced with impact on the ecosystems.
The catchment is instrumented since 1997 in particular in two sub-catchments with different land uses (Mercier: agriculture and forest) and Chaudanne (agriculture and urban) with rainfall and discharge data. Some information about physico-chemical characteristics are also available.