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) long term observatory. It is representative of French periurban areas and is characterized by a marked topography. 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 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 urbanization is observed since the seventies. 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 rain water is mainly collected through combined sewer systems, equipped with combined sewer overflow devices (SOD) that overflow in the river when the sewer capacity is exceeded. This water 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 urbanized areas via SODs. Increased erosion of the river banks has also been evidenced with impact on the ecosystems.
The OTHU observatory is an interdisciplinary platform that documents in situ water and contaminants fluxes generated by the city or by urbanizing areas during dry or rainy weather. It also studies their impacts on aquatic environments (small rivers and groundwater). The Yzeron catchment is representative of periurban catchments with small intermittent rivers. Using the observations collected in the catchment, the following objectives are addressed:
- Improve our knowledge of the water cycle in periurban areas, in particular through integrated modelling including sewer networks;
- Improve the knowledge of rainfall variability and the resolution needed to understand hydrological processes in periurban catchments;
- Assess the hydrological and ecological impact of artificialization of periurban areas;
- Document and model water and pollutant fluxes and their fate in the river /hyporheic compartments of the system;
- Study interactions between river and artificial networks during urban flooding events.
Sites and measured variables
The research instrumentation that started in 1997 in the Yzeron catchment is complementary to operational networks of Lyon Métropole (5 rain gauges at 6 min from 1985) and from DREAL (two stations draining 48 and 129 km2 since 1969 and 1988 respectively). It includes 5 rain gauges (1997, 2005, 2008), one meteorological station (2008) and 5 nested sub-catchments (discharge, water temperature): Mercier station (1997 – 6.8 km2, forest and agriculture), Chaudanne upstream SOD station (1997 – 2.1 km2, agriculture and urban), Chaudanne Léchère station (2005 – 4.1 km2, more urbanized), Ratier station (2010, 19.2 km2) and Charbonnières station (2009, 23.2 km2), plus discharge in the sewer network (Chaudanne since 2000). Since 2017, monthly measurements of physico-chemical parameters, metal and bacteria contents are sampled at three locations in the Mercier and Ratier catchments. Two soil moisture profiles have also been installed in the Mercier. In the Chaudanne catchment , a site has been instrumented since 2000 to study the impact of the SOD. Measurements of physico-chemical and microbiological parameters have been acquired during campaigns and projects on this site.
Partners and further information
The monitoring of the Yzeron catchment is performed by INRAE (Unité de recherche RiverLy) and the Laboratoire d’écologie microbienne (LEM, CNRS/Lyon 1/INRAE/VetoAgroSup/BioEnvis/IdexLyon2016). OTHU is funded by Lyon Métropole, Rhône-Méditerranée & Corse Water Agency, the Ministère de l’éducation nationale, de la jeunesse et des sports and the Région Auvergne Rhône-Alpes. SAGYRC also provides funding for the Yzeron catchment monitoring. The OTHU is a workshop site of the Zone Atelier Bassin du Rhône (ZABR).