Coastal dunes development on an industrial port complex, the example of the Port of Dunkirk, Northern France

Transcription

1 Colloque international Gestion des dunes côtières Merlimont juin 2014 Coastal dunes development on an industrial port complex, the example of the Port of Dunkirk, Northern France Gestion des dunes littorales sur un complexe industrialoportuaire, l exemple du Grand port maritime de Dunkerque, Nord de la France A. Tresca 1, M-H. Ruz 2 1 IDRA Environnement Centre d affaires CREANOR, 2 route de Bergues, Coudekerque-Branche antoine.tresca@idra-environnement.com 2 Laboratoire d'océanologie et de Géosciences, UMR CNRS 8187 LOG, 28 avenue Foch, Wimereux, France ruz@univ-littoral.fr

2 Located 40 km from the English port of Dover, 10 km from Belgium, the port of Dunkirk extends along a frontage of 17 km Photo: PAD 1994 Western Harbour Eastern Harbour

3 An artificial shoreline Etat Major map from the mid 20 th century, the blue line corresponds to the presentday shoreline. Source : Geoportail, Serveur de visualisation de données géographiques et géolocalisées, IGN 2012 The extension of Dunkirk port since the mid 20 th century resulted in the creation of an artificial shoreline.10 km² of land was reclaimed from the sea. Aerial photograph of 1932 and present-day shoreline (blue line). Source : Sextant, Serveur de donnée géoréférencées marines, Ifremer 2011

4 Eastern harbour: «La digue du Break» was built in 1963, to protect a deep-water basin Construction of a 6 km long dike (source : archives GPMD, 1962) A very popular site.

5 1994 Photo PAD Construction of the Western harbour , the «Canal des Dunes» was excavated, creation of a sand platform Source: Objectif Vidéo Photo GPMD 2010 Today, a «natural» area, with protected species (Eryngium maritimum, little tern )

6 Beach and coastal dunes Asphalt dike Photo : Ruz 2010 Photo : Ruz 2005 Plage du Clipon Digue du Break

7 Dunes du Clipon: Incipient and established foredune development Photo : Ruz 2009 Photo : Ruz 2005 Source: Tresca, 2013

8 One of the aim of this study was to test the efficiency of sand fences in order to enhance coastal dune development Source: Tresca, 2013

9 Source: Tresca, 2013 Most of them rapidly captured a large amount of sand, especially sand fences erected well above the highest water levels

10 Landward slope dunes Dike crest dunes Basin edge dunes Dike toe dunes Several types of dunes were identified. According to Nordstrom ans Arens (1988) they are opportunistic dunes, resulting from unintended human actions. On the dike, «coastal» dunes also naturally developped. The «digue du Braek» was built in 1963, and in 1988 dunes were covering an area of 7900m².By 2009, the cumulative area of dunes was reaching m². Source : Tresca, 2013

11 Sand accumulation updrift the jetty allowed the formation of a wide upper beach and embryo dunes development at the toe of the dike Dike toe dunes formation m² in 1983 > m² in 2009 Source: Tresca, 2013 Orthophotoplan I2G PPIGE

12 Basin edge dunes Under direct onshore winds, aeolian sand transport from the upper beach to the lee side of the dike resulted in the formation of what we called «basin edge dunes» Dunes de bordure de bassin Source: Tresca, 2013

13 Landward slope dunes Dunes de revers de digue Source: Tresca, 2013

14 (Clichés, Tresca, 28/07/2010) Here dune formation was initiated by Ammophila arenaria germination in numerous cracks, parallel to the dike slope. Vegetation growth was possible as, beneath the asphalt coating, the core of the dike is sandy. Vegetation trapped sand wind-blown from the adjacent sandy beach, resulting in the formation of parallel lines of embryo dunes along cracks. Sand then continues to accumulate and progressively embryo dunes coalesced resulting in the formation of continuous dunes covering the landward face of the dike (Tresca et al., 2014).

15 Dike crest dunes In the central part of the dike, dike landward slope dunes developed and reached the crest of the dike forming a ridge of 1 km long that covered the dike crest.they exceed 2 m above the dike crest elevation and are well stabilised by marram grass. Their morphology is quite similar to a foredune ridge. Dunes de sommet de digue Source: Tresca, 2013

16 Sand transfer from the seaward to the landward face of the dike is still active and requires costly dredging and removal operations. In 2010, for example, m 3 of sand was removed from a 500 m long road section at the landward toe of the dike (Tresca, 2013).

17 Sand fences were erected on the dike in order to limit sand drifting. The most efficient fences were the fences installed close to a sand source, at the beach-dike contact (D1), and behind the dike-toe dune deflation corridors (D5 D6). Less efficient fences were synthetic mesh and wooden slats installed mid-slope on the seaward face of the dike. Source : Tresca, 2013

18 Cakile maritima (A et B) and Eryngium campestre (B) (Tresca 28/07/2010) Naturally developing dunes on harbour infrastructures could help to improve the diversity of landscapes along such human-altered shorelines. In Dunkirk seaport, dune development on the dike favoured natural development of protected species like Eryngium campestre. Furthermore, in a context of climate change inducing sea level rise, dune development on the crest of a sea dike can act as a buffer during storm surges and prevent dike overtopping by storm waves. These experiments will enable the Port of Dunkirk to build a management plan of its shoreline, in order to preserve the diversity of landscapes, habitats and species and meanwhile, to control sand invasion on the dike and reduce costly sand removal operations.

19 Photo : Ruz 2014 Photo : Ruz 2014 These results will also help in coastal dune rehabilitation, after the construction of a gas terminal. The Dunkirk LNG terminal will have an annual regasification capacity of 13 billion m 3 of gas, representing around 20% of France and Belgium's annual natural gas consumption. Photo : Ruz 2014 Source: DKLNG, avril 2014

20