Dredging, a necessity
Due to tidal currents and variations in the flow of the Seine, sand and mud enter or move around in the river. Most of this sediment returns to the sea but some of it settles to the bottom.
If the Port did not take action, the channel would become partially blocked by these sediments and would no longer allow commercial ships to pass through.
Dredging operations are therefore carried out throughout the year. They consist of removing this sediment from the shipping channel and berths so that ships can safely navigate and dock in the harbour.
On average, 4.8 million m3 of sediment are dredged each year to maintain nautical access to the Port of Rouen.
Depending on the sites and their exposure to the currents, the sediments resulting from maintenance dredging are of different natures:
- in the downstream part of the estuary, from the mouth of the Seine to Vieux-Port, they are a mixture of sand and mud brought by the tide (which represent 90% of the volumes dredged).
- in the upstream part of the estuary, from Vieux-Port to La Bouille, they are generally made up of sand.
- in the upstream port area, from La Bouille to Rouen, they are mainly made up of mud.
The dredged sediments systematically undergo physico-chemical analyses carried out by an approved independent laboratory. The results show that they meet the various standards set by the regulations.
The dredging operation
Dredging operations are mainly carried out by suction dredgers. These ships travel at low speed while sucking sediment mixed with water through a long pipe called a suction tube. The dredgers remove the water and then store the sediment on board in wells. It is then transported and deposited either at sea (referred to as immersion or dumping) or on land.
Dredging operations are mainly carried out by suction dredgers. These ships travel at low speed while sucking up sediment mixed with water through a long pipe called a suction tube. The dredgers empty the water and then store the sediment on board in wells. It is then transported and deposited either at sea (referred to as immersion or dumping) or on land.
The Port of Rouen manages the dredged sediments according to their nature and location:
- The sediments dredged in the lower estuary are deposited at sea. This is called dumping. Since 1977, it has been deposited at the mouth of the estuary, at the Kannik site. Since 2017, it has been deposited at a new site, Machu, located 11.5 km from the mouth of the estuary. A small amount is deposited ashore at a transit site in Honfleur for recycling in the construction sector.
- The sediments dredged in the upper estuary are deposited on land. The coarser sediments are discharged into one of the 5 transit facilities in Honfleur, Lillebonne, Saint Wandrille, Jumièges or Moulineaux. The finest sediments are used to fill former sand and gravel quarries in water (gravel pits).