Sete site description

Goal of the monitoring site

Along the Mediterranean coasts, new soft techniques of defence against coastal erosion have been deployed over the last decade, such as geotextile wave breaker, groins and beach dewatering systems. The evaluation of the effectiveness of these techniques in microtidal environments remains rare as it is difficult to link the observed changes to presence of the structures. This is mostly due to the lack of frequent data on morphological and spatial distribution of near shore waves and currents.

At the site of the Lido of Sete a number of these techniques were implemented to protect the local beach and beach road. This popular beach was restored after significant loss of sand and damage to the local road. The location provides an exceptional full scale laboratory to analyse coastal behaviour associated with these soft defences.

Figure 1 - Design of the location at Sete (taken from Balouin, Longueville, Colombet 2015)

The Argus video monitoring system

To monitor the shore dynamics and near shore morphodynamics at a high frequency, an Argus video monitoring station was installed by BRGM and Sete Agglopole Méditerranéein 2011 and has been operational ever since. The Argus system consists of two 20 meters high masts with 8 cameras (indicated as Mat 1 & 2 in the image). The masts are 2.5 km apart. The images of both masts are merged to cover over 3 km of the area of interest.

Figure 2 – snapshots and combined rectified images from the 8 cameras.

From the images, the coastline and the presence and evolution of nearshore bars are detected and wave and currents are analysed. The figure below shows the evolution of the nearshore bar pattern and the shoreline before and after the implementation of a geotextile submerged breakwater.

Figure 3 - timex Images illustrating the response of the bar/shoreline to the implementation of the geotextile submerged breawater (Bouvier et al., 2017).

Results and future work

The monitoring of the Lido of Sete beach before and after the deployment of soft defenses permitted to obtain a very detailed and quantitative information on the nearshore bars and beach response to the geotextile. Monitoring is still on going.

BRGM is presently looking into the applicability of cBathy in this area. Cbathy derives waves from the images and determines the underlying bathymetry though wave inversion.

References

  • Bouvier, C., Balouin, Y. et Castelle, B. Video monitoring of sandbar-shoreline response to an offshore submerged structure at a microtidal beach. Geomorphology: 295: 297-305.

  • Bouvier, C., Balouin, Y. et Castelle, B. Nearshore bars and shoreline dynamics associated with the implementation of a submerged breakwater: topo-bathymetry analysis and video assessment at the lido of Sète beach. Coastal Dynamics 17: 534-543.

  • Balouin, Y., Longueville, F. and Colombet, Y., 2016. Video assessment of nearshore and beach evolution following the deployement of a geotextile wave breaker. SI 75. J. of Coastal Research, pp. 617-621 .

  • Balouin, Y., Longueville, F. and Colombet, Y., 2015. Video monitoring of soft Coastal defenses at the lido of Sète, France. Proceedings of CM² International conference, Paralia, 191-196.

  • Balouin, Y., Rey-Valette, H. and Picand, P-A., 2014. Automatic assesment and analysis of beach attendance using video images at the Lido of Sète beach, France. Ocean and Coastal Management, 102:122-144.

  • Gervais, M., Balouin, Y. and Certain,R., 2013. The major control parameters of storm morphological evolution on a micortidal beach. Proceedings of 7th Coastal Dynamics Conférence, Arcachon, 24-28 June 2013, pp. 151-160.

  • Balouin, Y. and Gervais, M., 2013. Morphological feedback between nearshore bars and shoreline dynamics during storm events – video observations at Sète beach, France. Proceedings of 7th Coastal Dynamics Conférence, Arcachon, 24-28 June 2013, pp. 151-160.

  • Balouin, Y., Tesson, J. and Gervais, M., 2013. Cuspate shoreline relationship with nearshore bar dynamics during storm events – field observations at Sete beach France. Journal of Coastal Research. SI65(1): 440-445.

  • Gervais, M. Balouin, Y., Thiebot, J., Certain R., Bélon, R., Pedreros, R., Robin N. and Berne, S., 2011. Morphodynamic evolution of nearshore bars in response to winter storms (Lido de Sète NW Mediterranean. Journal of Coastal Research, SI 64 (2011) 1855-1860.

  • Gervais, M., Balouin, Y. and Belon, R., 2011. Morphological response and coastal dynamics associated with major storm events along the Gulf of Lion Coastline, France. Geomorphology, 143-144: 69-80.