Journal of Coastal Research 175-184 Royal Palm Beach, Florida Winter 1998 The High Sands of the Danish Wadden Sea-Especially the Ebb-Tide Delta, Soren Jessens Sande, and its Incorporation with the Island of Fane N. Kingo Jacobsen Institute of Geography University of Copenhagen 0stervoldgade 10 DK-1350 Copenhagen K, Denmark ABSTRACT _ JACOBSEN, N.K., 1998. The high sands of the Danish Wadden Sea-especially the ebb-tide delta, Seren Jessens ,tflllllll:. Sande, and its incorporation with the island of Fane. Journal ofCoastal Research, 14(1I, 175-184. Royal Palm Beach (Florida), ISSN 0749-0208. ~.~ ,., A 7f This article attempts to accountfor the coastal morphology south of Blavandshuk,western Jutland, Denmark.This coastal section is dominated by a barrier beach development, behind which lies the Danish part of the Wadden Sea. There is a description of the results of borings that were made in order to understand the dynamics at work since the very first offshore bar development. The effectof the changingsea-level since the Weichsel Glaciation, which has been accompanied by differenttidal conditions and stormfloods of varying magnitude during the past 3000-8000years is also described. The originand balanceofsediments is dealt with;especially the high sands and shoalsofthe DanishWaddenSea with particular reference to the evolution of the ebb-tide delta, Seren Jessens Sande, which is described in detail with the use of maps. Howand when its incorporation with the island of Fane took place is described. ADDITIONAL INDEX WORDS: -Coastal morphology, sediment transport, sedimentary budget, barrier island, bar, shoal. INTRODUCTION series of deepwater channels that function as water exchang­ If Denmark, within the Nordic context, is to be considered ers between the North Sea and the Wadden Sea which lies representative of a geomorphological landscape complex that between the barrier islands and the mainland. The Wadden contributes to the Scandinavian sub-continent as a whole, it Sea consists of several basins each with networks of dendritic is without doubt because of the coastline to the south of Bla­ channels (the Danish priel channel systems). In relation to vandshuk in southwest Jutland with its estuaries, saltmarsh the tide, the priel channel networks behave like pulsating and tidal flats. The barrier islands of Skallingen and the bellows or the lungs of the sea. Figure 3. north Frisian Islands are found here too. Figure 1. (II) The sediment that has built the Wadden Sea tidal flats Located in this unique natural area is the field station originates from further along the coast or the North Sea. It Skalling Laboratory, owned by Copenhagen University Ge­ is transported to the Wadden Sea by the coastal current, ography Institute. It represents an important research centre waves and tides. Vast volumes of water are sucked into the studying the dunes, tidal flats and saltmarsh. The high sands Wadden Sea at high tide through the priel channel networks represent one of the special landscape elements under study. and sucked out again at lowtide (Figure 3). The high sands An account of their genesis and dynamics necessitates an un­ are important landforms in this coastal zone. Their distri­ derstanding of the entire set of coastal geomorphological pro­ bution relates to the continuous battle between the ingoing cesses. Figure 2. and outgoing water masses, and in particular to the position The current picture of the coastal dynamics, involving the in­ of the dendritic flood and ebb tidal channel networks. The teraction of waves, tides and sediments, represents but a fleet­ high sands are thus determined by both flood and ebb tidal ing point in time in the overall development of the changing conditions. Nevertheless, it is essential to understand that coastline of the North Sea. The coastal zone studied stretches the high sands are a product of both current coastal dynamics southwards from Blavandshuk on the west coast of Denmark to as well as much older processes; such as the origin and evo­ Den Helder in Holland. From the mainland, it extends seawards lution of the Wadden Sea itself once the North Sea became (westwards! as far as the 10m deepwater mark. post-glacially tidal-that is to say that the North Sea was THE COMPLEXITY OF THE WADDEN SEA re-established as a consequence of the post-glacial sea-level COASTAL ZONE rise in the Atlantic Period. (I) In the west, the coastal zone consists of a row of barrier (III) Borings taken from the barrier island complex have islands called the Frisian Islands. They are separated by a helped ascertain the genesis of-the whole region (Figure 8). Useful datings have fixed the chronological development. 96034 received and accepted in revision 6 April 1996. Post-glacially, the Wadden Sea was initially a gigantic la- 176 Jacobsen Ebbevej . Ebb · raad Olernning, Dam Grcense , Fronti~r ... "'....£ ......4. Skrcen t, Cliff 'RIBE= F---------------------q Klit, Dune san ds REJS8Y OIGE Bakken, Old mO/dine l­ w '"w o Hedeslette. SKA:RBA:K Out wAsh plain Mars k . ssu: marsh .. .... , ... 1". ".."'.. .. ''1.,. Vade. Tida' flill Figure 1. The Danish Wadden Sea. The dashed line represents th e littoral equilibrium line. a. Gradyb Knudedyb Juvre Dvb Lister Dyb Total km' % km' % km? % km" % k rn! % Total area 126 15 164 20 131 15 415 50 836 100 Tidal-flats 76 60 127 77 112 86 274 66 589 70 b. Gradyb Knudedyb Juvre Dyb Lister Dyb mill.m' rnill.rn" mill.m' rnlll.rn! Outgoing 145 175 150 ab, 525 Ingoing 130 180 160 abo 525 Rest current to Ihe North + 15 - 5 - 10 Figure 2, Statistics on the Danish Wadden Sea: (a) tidal area water balances (b) the tidal prisms, Journal of Coastal Research. Vol. 14, No, 1, 1998 Coastal Morphology in Jutland 177 A H.W . MIGRATING SHOAL BARS LW BAR9 L.W. STABLE OUNE LAGOON LW BARRIER SEA WADDEN MARSH PRIEL . :.. - . .... ' B - OIAEClM)N 01" TJO~ -. EBB-OOMINATED .. ..'.. ', '.' , TIDAL CVRAtN1S nOAl WAIEIitSHEO cw.... HnOfl Figure 3. Models of the Danish Wadden Sea showing: (a) the creation of barrier islands and the Wadden Sea caused by rising sea-level (b) the circular transport pattern of fine-grained sand. (redrawn from Carter, 1988). goon in which peatbog developed. Approximately 3,500 Be rial by the aforementioned processes has led to the barrier the bogland was invaded by mixed oakwoodland. Later, this island chain and west coast dune landscape as we recognize was transgressed by the sea. Borings off the coast at Ballum them today . Several points along the west coast of Jutland show the upper 10-50 em to consist of tidal-flat sand below have functioned as hooks to which the Wadden Sea barrier which there is a layer of peat and the remains of the former island chain from Skallingen to Sild has attached itself. mixed oakwoodland; oak, hazel, birch. This layer lies above These points are; Blabjerg, Hjerting, Hornsrev, Emmerlev, the earlier podsolized outwash plain (JACOBSEN, 1964). Fig­ Sild, Fehr, Amrum, Eiderstedt (Set. Peter). ure 4. It is thus a very dynamic landscape which is under discus­ sion. The Wadden Sea is an important element. Its creation CREATION OF THE WADDEN SEA is a result of tidal action behind the barrier island chain. The The formation of the barrier island chain started with the tidal waters have cut channels in the island barrier. Twice creation of beach ridge systems in the Skallingen, Fane and daily, 1 cubic kilometre of water passes backwards and for­ Rarna area that now lie at a depth of 25-30 m as confirmed wards through the 4 deeps. The tidal range is about 2 m at by borings (Figure 8). The continuous arrival of more mate- Hejer and 1.5 m at Esbjerg. Journal of Coastal Research, Vol. 14, No.1, 1998 178 Jacobsen R0M0 M0LBY HAVNEBY (2) m m m m +3 +3.0 +0.8 0 silt blown sand - 1.1 0 0 sano.coarss clay -0.8 -3.2 -20 sill and line sand clayey silt -4.5 -5 -5.4 peaty sand shells send. medium - 5 -7.4 sand and clay rarnina ted -6.3 -83 stony gravel - 10 -9.7 sand and gravel sand - 10 -12.4 -10.5 slony sand shells -13.5 clay - 12.0 -139 -15 silt sand and gravel - 15 -182 - 17.0 sand. fine sill and line sand - 20 -22.4 sill -21.0 -23.4 silt and line sand -24.3 -25 - 25 clay - 30 -290 ~::.~ ::.;.~., - 30 .' •... !t •.•" •. '4. ,0: .0· •..• 0 sand and gravel - 35 D.··:". ..-. - 35- 0,",0 : "'~" ~ - 37.0 Figure 4. Borings from the barrier island complex (Skallingen-Fan0-Mand0-R0m0). Skallingen lies above the Eem layer, located at minus 21.8 m DNN (Nordmann, 1928), and Manda above the black-brown Tertiary clay, located at minus 23.5 m DNN. On the other hand, Fane and R0m0 lie above trangression layers of gravels and stony sands located at minus 20 m DNN and minus 29 m DNN, respectively. The general pattern is the regular alternation of transgression and regression layers that occurs in all boring samples. The first change occurs between a depth of minus 8 m and minus 10 m DNN. The regression layer of clay or clayey sand is usually between 3-10 m thick located at a depth between minus 29 m and minus 14 m DNN. Finally, regression layers, usually comprising peat, are found everywhere in the horizons minus 7-8 m DNN and minus 4-5 m DNN. The barrier consists therefore of an interesting "sponge cake" reflecting the climatic fluctuations of the post-glacial era. However, the total picture lacks the effect of storm­ floods, which play their part in climatic fluctuations.