Abstract
Tidal sand banks are common along the coast of northern France facing the North Sea, where they form linear shore-parallel or slightly oblique sand bodies from shallow coastal areas to depths of tens of meters. Hydrographic surveys have been carried out since the 1830s for mapping the seabed of the coastal zone. An analysis of the bathymetry evolution shows significant morphological changes have occurred across the shoreface since the early 19th century, largely due to cross-shore and longshore sand bank migration. Our results show that nearshore sand banks mainly migrated onshore and gained sediment, especially during the 20th century; acting as temporary sediment sinks, which can in turn serve as sand sources for providing sediment to the coast. Alongshore, the migration and elongation of sand banks can be related to tidal asymmetry that is mostly directed to the east-north-east in the region. Shore-perpendicular movement can likely be explained by the action of shore-normal storm-waves in the nearshore zone after their refraction over shallow offshore sand banks. A seaward displacement of sand banks was also observed. This may be related to the combined action of waves and tidal currents which can induce erosion on one side of the bank, decreasing its width, and eventually leading to its seaward migration. Our observations point out that some nearshore sand banks respond to the action of currents and waves, and interact between each other via feedback morphodynamic processes induced by sand bank morphological changes. The substantial morphologic changes that affected the nearshore zone of northern France during the last centuries probably had large impacts on coastal hydrodynamics and associated shoreline evolution.
Highlights
Different types of tidal sand banks are present in a wide range of water depths from the outer continental shelves to the shallow coastal environments, and several theories have been proposed to explain their origin and maintenance
In order to better understand the large-scale evolution of this area, which is exposed to strong hydrodynamic forcing, this study aimed to analyze the evolution of the nearshore morphology between the Belgian border and the Dover Strait (Figure 1) and to assess the potential impacts of changes in sand bank morphology and position on coastal dynamics
This paper presents a large-scale evolution of nearshore and offshore sand bodies located in the macrotidal environment of the southern bight of the North Sea
Summary
Different types of tidal sand banks are present in a wide range of water depths from the outer continental shelves to the shallow coastal environments, and several theories have been proposed to explain their origin and maintenance. As well as storm-generated shear stress, and the post-glacial rise in sea level, have all been called upon as mechanisms that are responsible for the formation of sand banks [1,2,3,4,5,6,7,8]. Tidal sand ridges are a characteristic feature of tide-dominated continental shelves, with large available sand volumes. Their generation requires a source of mobile. ElEolnognagtaetetitdidalalbbaannkkssaabboouunnddinintthheessoouutthheerrnn NNoorrtthh SSeeaa [[22,,55,,1100––1133]] ((FFiigguurree 11iinnsseett))aannddmmaayybbee eiethitehreracatcivtieveoromr moroibriubnudn.dA. cAticvteivseasnadnbdabnaknskasreargeegneenraelrlayllfyorfmoremdeadt awtawteartedrepdtehpsthshs aslhloawlloewr tehratnha3n0– 5030m–5, 0wmhe,rwe htiedrael tciudrarlecnutsrraernetsstarroensgt,reoxncge,eedxicnege0d.i5ngm0·s.−51 m[14·s]−, a1 n[1d4m], aayndmmigaryatme iingrraetsepionnrseestpoopnrseesteont hypdrersoednytnhaymdircopdryoncaemsseics p[9r,o1c5e,1s6se].sM[9o,1ri5b,1u6n]d. sManodribbuannkdssaarnedgebnaenrkasllyarpergeseennetrainllydeperpeesrenwtaitnerdsewepheerre thweactuerrsrewnthreergeitmhee cisurtroeonwt reeagkimtoe cisautosoe awcetiavketsoecdaimuseenatcmtivoevesmedeinmt,eonrt minovloewm-eennte,rogryinshlaolwlo-wenweragtyer arsehaasll[o9w,17w].ater areas [9,17].
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