Caractérisation hydrologique et microbiologique du bassin versant de Sainte Anne (Plouzané)

The coastline has many activities related to water quality such as bathing activities. Coastal catchments are known to be source of microbial input to the marine environment, their flows and runoff bringing important quantities of sediment, bacteria and other particles. Thus, a network of monitoring and modeling may be necessary to prevent economic losses such as a closure of beaches due to contamination. Hence, within the framework of project GIRAC, a modeling of river and E. coli flow in the Sainte-Anne catchment was developed. To implement the model AVSWAT on the catchment, a data collection (stream gauging, E. coli analyses) and work on GIS was necessary. The aim of this study is the hydrological and microbiological characterization of the catchment. The Sainte-Anne catchment spread over 5 km² as a characteristic of being mainly covered with arable land and urban areas. Its rivers have a deteriorated water quality based on the parameter E. coli and they suffer frequent point source pollution (waste water treatment plant and failing septic systems). Moreover, when heavy rainfall (about 2-3 mm/h), its main stream, the Nevent, suffered significant damage due to microbiological runoff on arable land, pasture and urban areas. It also has a low speed, that could triple, reaching a peak flow (about 0.12 m3/ s) in case of heavy rain. The surface runoff lag time of the catchment is very short (2-3h) and E. coli flows of 5,8.108 ufc/m3/s have been observed at its outlet, impacting undoubtedly the quality of coastal waters.