Projects

Background

Since 2001, high concentrations of bacteria have been found in shellfish harvested in the Aber Benoît estuary. The effect has been to reduce the number of shellfish sold commercially, dampen the local shellfish economy and cast a shadow on the reputation of the Abers in general.

Against this background, the intermunicipal authority, Communauté de Communes de Plabennec et des Abers, decided to commission a study to determine the causes of shellfish contamination incidents and the circumstances in which they occurred.

Services provided

SAFEGE began by building a model to analyse hydrodynamic processes in the estuary and assess water exchange and flushing in shellfish waters. At the same time bacterial loadings from tributaries, treated sewage and stormwater discharges, agricultural runoff, on-site sewage disposal systems and industrial effluents were assessed.

A first series of simulations was conducted to determine the risk of shellfish and bathing water contamination from different sources and in different tidal and wind conditions. At the same time the model itself was assessed to determine its sensitivity to hydrodynamic simulation parameters.

Shellfish contamination processes were then evaluated based on simulations over a single lunar cycle. The results demonstrated the extent to which contamination varied with loadings from different sources and with tide and wind conditions.

Finally, longer- term simulations (over two months) were performed to examine shellfish and bathing water contamination in realistic load, wind and tide conditions.

The study thus made it possible to determine the vulnerability of shellfish waters in the estuary, while clarifying the impact of the different sources of contamination and the limits of the insights to be derived from the model.