OZCAR-RI SNO_Karst : Karst Craie - France
OZCAR-RI SNO_Karst : Karst Craie
Parent Site Name
The Chalk Karst observatory groups different karst sites on the Cretaceous Chalk located at the Paris Basin (Norville, Radicatel, Yport, Saint-Martin-Le-Nœud). These karst watersheds range from 10 to 200 km2 and the land use consists of agriculture and grazing under oceanic climate. There are characterized by chalk plateaus covered with clay-with-flints owing to chalk weathering constituting a fairly impervious layer and with quaternary silts. These surficial formations range from 3 to 20 meters depth and are highly susceptible to crusting, compaction, and erosion, particularly during autumn and winter. A numerous swallow holes locally penetrates the chalk through the above-mentioned impervious layer, resulting in a strong connection of the surface with the aquifer inducing infiltration of turbidity releases at spring and well used to drinking water (up to 500 NTU). These Chalk karst sites are one the sites of the French SO-KARST labellised by INSU-CNRS and are a part of the French RBV-Network and ZA Seine.
General Characteristics, Purpose, History
Norville karst site is located at 40 km of Seine estuary on the right river bank. It composed by three sampling sites : i) a swallow hole on the chalk plateaou where Bebec creek water (10km2) is fully infiltrated in a geological fault, ii) a spring on the foot of the chalk plateau at the contact with Seine alluvial deposits which is hydrologicaly connected with the swallow hole, and iii) a well in the Seine alluvial deposists which is drilled in the chalk for drinking water supply. The norville chalk karst hydrodynamic depends to tidal range in the Seine river. Radicatel spring is located at 20 km of Seine estuary on the right river bank and Yport well is located in the chalk plateou near the Channel sea. They supply Le Havre city in drinking water after sanitation by treatment stations due to turbidity, microbiology and pesticides releases. The watersheds (200 km2) are composed by numerous farming and houses with septic tanks. They are penetrated by numerous swallow holes (up to 500). These three chalk karst sites allow to improve knowledge on i) the role of surficial cover in fast and low infiltration into the chalk, ii) the links between the porosities of matrix, fissure and karst conduit (water quantitiy and quality exchanges), iii) the impact of tidal range on karst hydrodynamic and transfer, iv) the relationships between piezometric variations and climate indices, v) the transfer of turbidity and environmental microbiology to evaluate sanitary risk.
Affiliation and Network Specific Information