In a macrotidal environment, the Authie Bay near Berck sur Mer, France, is characterised by meanders of the coastal river which regularly threaten the dunes of Bois des Sapins on the right bank. Strong erosion occurred in 2011 and 2018. The meander approaches and erodes the dunes under the combined action of currents and waves. During these events, many trees fell on the beach. The dune cordon loses an average of 10 m of sand. The littoral drift pushes the sandbanks and the river towards the coast as long as the river does not manage to cut the bank with tidal currents and too low river flows.
In an attempt to reduce this coastal erosion, a flexible development prototype has been implemented in the bay as part of the ENDURE project. The system is made up of nets which reduce currents and thus promote deposits. The low porosity system provides turbulent dissipation of the kinetic energy of the currents through multiple threads assembled in the shape of an inverted ‘V’. The sediments are trapped near the bottom through successive layers. The net (100 m long) was installed in March 2019 and morphological development monitoring was implemented. After 3 months, the main channel was pushed 50 m off the shore, and deposits of 0.5 to 1 m were observed in the area of the development. Between 3 and 6 months, the configuration had stabilised.
Due to its limited length, the development has a local effect of protecting the cove of the Bois des Sapins. However, the development proved to be effective throughout the year of the experiment and met the objectives set for it, namely to push the main channel offshore.
In view of the cyclical effects of the Authie's meanders, a longer trial period is recommended to confirm the effectiveness of the system over the long term. A greater length of the device is also recommended to maintain the river permanently offshore on the entire north shore of the bay.