The seismic data acquired during the Stockline survey mainly aimed in estimating the volume of sediments available for the natural supply of coastal areas of the Normandy coasts. This task was part of the Regional SELINe project and Elise Grenard-Grand's PhD.

Although Elise Grenard-Grand abandoned her PhD in October 2021, all the seismic data from Stockline 19 were processed and analyzed. Thanks to these data, in addition to other seismic data acquired during previous survey and which Elise Grenard Grand had listed and used (Figure 3), isopach maps of soft sediments (sandy) above a substrate considered as "non-remobilizable" were produced. These maps thus made it possible to define, at the scale of the Normandy coastline, the areas rich in mobilizable sediments and those devoid of sediments (Figure 4).

Furthermore, these seismic data and the comparison of old bathymetric data served as a basis for defining the major trends in the evolution of available sand reservoirs since the beginning of the 19th century. The results obtained, not currently published (a publication almost completed at the time of Elise Grenard Grand's abandonment, has yet to be finalized and submitted: Grenard-Grand et al. Long-term mobility of subtidal sand stocks, combination of seismic and bathymetric data, Normandy, France), show several evolutionary trend patterns (Figure 5). Very generally, in the Seine Bay domain (from the NE Cotentin  to Antifer), 2 modes of evolution occur: stocks in the outermost cells are rather stable or in accretion, while those in the most coastal cells, with the exception of those associated with the mouth of the Seine, are subject to strong to moderate erosion, or are stable. In the Northern Seine-Maritime region, sediment stocks in all cells are stable or eroding since 1830 (with the exception of the areas closest to the mouth of the Somme, which are in accretion). More precisely, stable areas are in the southwest and gradually shift to increasingly eroding areas towards the northeast. However, this SW-NE gradient is reversed for the most coastal cells. The interannual sediment flux data obtained from the comparative analysis of sonar or SMF data on sedimentary bodies such as hydraulic dunes generally confirm the trajectories of stock movements on a secular scale.

Note that all the coastal VHR seismic data acquired during the Stockline 2019 survey, in addition to data also acquired in the Bay of Mt St Michel and the Eastern Bay of Seine, made it possible to produce a synthesis of the different depositional architectures and construction steps of coastal sedimentary wedges associated with estuarine mouth context of the Normandy coasts of the English Channel (Tessier et al., 2020, ASF Brest; 2022, Tidalites 2022)

The surface sampling data in the "Orne" and "Antifer" boxes have not been used to date. The data from their analyses are the subject of part of Clément Frigola's thesis work (Intechmer).

Figure 3. Position map of all seismic surveys listed to assess the volumes of mobile sediment stocks along the Normandy coast (Grenard-Grand et al., in prep.; Grenard-Grand, 2021, PhD intermediate report; Lesourd et al., 2022, final report SELINe project)

Figure 4. Seismic profile (Boite Baie des Veys) indicating the method of identification of the depositional unit considered to be remobilizable (Unit 4). Isopaque maps of the sedimentary cover along the prospected coasts: at the top, for all the sedimentary units recognized on seismic lines above the geological substratum (mainly Holocene cover, even upper Pleistocene); at the bottom, for the sedimentary unit considered as remobilizable (Unit 4) (Grenard-Grand et al., in prep.; Grenard-Grand, 2021, PhD intermediate report; Lesourd et al., 2022, final report SELINe project)

Figure 5. Very general trends in the evolution (gain or loss) since the beginning of the 19th century of mobile sediment stocks along the Normandy coast, estimated from the recognition of remobilizable sedimentary units on seismic lines and from the comparison of bathymetric data (Grenard-Grand et al., in prep.; Grenard-Grand, 2021, PhD intermediate report; Lesourd et al., 2022, final report SELINe project)