EXCURSION WAASLAND POLDERS AND LAND VAN SAEFTINGHE

19/03/2013

Afternoon Program

Katrien Heirman - Iason Jongepier - Tine Missiaen - Peter Vos

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1. Drowned Land of Saeftinghe

2 Coastal evolution of the Province of Zeeland

Regional coastal evolution of Zeeland

The coastal landscape of the southwestern has been formed during the present interglacial time period – the Holocene. Due to extensive geological, archaeological and historical research which has been carried out in the southwestern part of the Netherlands during the past few decades, it has become possible to reconstruct the coastal landscape evolution and the increasing role of man in the landscape development. The sources of this reconstruction are the publication on the coastal genesis history of the province of Zeeland by Vos & Van Heeringen (1997) and the TNO report on the coastal delta in the southwestern Netherlands, 5000 years and retrospective (Vos et al., 2002).

The Holocene started about 11.500 years ago. The major driving force in the coastal genesis in this region was the relative rise in the sea level. In addition, the morphology (or geometry) of the early Holocene landscape (Pleistocene valleys and ridges), the locations of the tidal inlets and the courses of the rivers, the availability and supply of sediments, and human interference have played important parts in the shaping of the coastal landscape of the Netherlands.

The Holocene drowning history of the southwestern Netherlands has been visualized in a series of 12 palaeogeographic maps for the period 5500 BC till present. The palaeolandscape maps could be reconstructed by using geological, archaeological and historical data.

10000-8000 BP (9000-7000 BC): Continental

phase (before the marine inundation)

At the beginning of the Holocene the sea level was very low (over 35 m below the current mean sea level). England was still

connected to northwestern Europe through a land bridge. Sea-driven flooding did not yet occur in the coastal areas of the western

Netherlands and those days. As a result of the rapid rise in the sea level at the beginning of the Holocene – which was due

to the warming of the climate which caused large masses of land ice to melt off from the ice caps at the North Pole and the South

Pole – the area of the area was flooded. The first drowning in the lower parts of the western Netherlands - the

Rhine- Valley - took place about 9000 years ago.

8000-5500 BP (7000-4400 BC): Inundation 9000 BP and development of the tidal basin

During the first half of the Holocene the rise Holocene sea-level curve of the – Meuse area in the sea level in particular was the driving (after Hijma & Cohen, 2011)

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force in the evolution of the coastal landscape. As a result of the rapid rise in the sea level the major part of the

southwestern Netherlands was drowned. About 5500 BC this area had been 9000 BP changed into an extended tidal

landscape with tidal channels, mud flats, and salt marshes. The peat areas lay in the transition area between the tidal

area and the higher Pleistocene sands in 10.500 BP Brabant and Zeeuws-Vlaanderen. The Scheldt River merged during that time into the lower lying Rhine and Meuse fluvial flood basin. At about 4500 BC the sea reached the most far inland position in Zeeland.

4500-2500 BP (3100-600 BC): regressive coastal development, the largest extent of the “ Holland P eat”

From that time onwards the coastal evolution took a turn from transgressieve to regressive development. The decline of the rise in the sea level was the Drowning of the North Sea. Lines with arrow: location of the reason. The raising (elevation) of the coastline at 10.500 and 9000 BP. coastal area due to sedimentation

Black box: Territory of the Province of Zeeland outpaced the rise in the sea level. About 3000 BC this resulted in a strong silting- Purple box: Saeftinghe / area up of the tidal areas. This process caused that intertidal mud-flats, salt marshes and peat areas to expand seaward. During the next period the storage area - water storing capacity of the tidal area during high tide - decreased further due to sediment accretion and this led to considerable reductions in the tidal channels and the tidal outlets. Due to these reductions extended coastal barriers and dunes formed along the coastline. In the course of the next millennia these coastal barriers increasingly protected the tidal area in the hinterland from the sea.

An almost closed coastline was formed between 2000 and 1500 BC with coastal barriers and dunes. Only at those places where rivers such as the Scheldt flew out into the sea openings in the coastline (tidal inlets) remained. Due to this closing off the back-barrier coastal area became isolated from the sea and the coastal peat areas could expand strongly.

300-1000 AD: Inundation of the peat landscape and, for the second time, the formation of a tidal basin

The situation of an almost closed coastline with a couple of river outlets remained until about 500 BC. Between 500 BC and the beginning of our era the coastline in the present Zeeland gradually broke down and in the hinterland small “slufter-like” tidal areas developed . The breaking down of the coast line in Zeeland was connected with the deficiency of sediment which started to occur before the coast of Zeeland in those days. A Pleistocene headland which had been present before the coast of Belgium during a long time had supplied the sand for the coast of Zeeland until those days. In the course of the Iron Age this stock of sand got depleted. Before the coast of Zeeland a deficiency arose because sand was moved to the central part of the coast of Holland through tidal-driven

4 Palaeogeographical maps of the Province of Zeeland

8000-5500 BP (7000-4400 BC): Inundation and development of the tidal basin

5500 BC 4500 BC

4500-2500 BP (3100-60 0 B C) : r eg r es si v e c oas tal dev el opment, the l ar g est extent of the “Hol l and Peat” 3000 BC 1500 BC

500 BC 100 AD

Legend Beige: Pleistocene outcrop, sand Yellow: Barrier ridges / dunes Blue: North Sea, tidal channel, river channels Light Green: Intertidal area, sand and mudflats Purple box: Saeftinghe / Doel area Green: Supratidal area, salt marshes Grey area: Belgium Brown: Peat bog 5

300-1000 AD: Inundation of the peat landscape and, for the second time, the formation of a tidal basin 500 AD 1000 AD

1000 AD – present: Period of human influence 1250 AD 1500 AD

1750 AD 2000 AD

Legend Beige: Pleistocene outcrop, sand Yellow: Barrier ridges / dunes Purple: Embanked areas (‘’polders’’) Light Green: Intertidal area, sand and mudflats Blue: North Sea, tidal channels, river channels Green: Supratidal area, salt marshes Purple box: Saeftinghe / Doel area Brown: Peat bog Grey area: Belgium

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coastal currents. The coastal barriers and dunes before the coast of Zeeland were used to meet this deficiency of sand. Because of this coastal erosion occurred, the coastal barrier breached and the sea could locally penetrate the peat areas in the hinterland. The sea did not yet reach far because the peat in the hinterland had grown up to 1 m or more above the maximum storm surge level.

Man took advantage of new situation of the landscape in Zeeland. During the Iron Age, but in particular during the Roman times (around 100 AD) the tidal channels through the coastal barriers were used to drain the high peat areas in the hinterland. Ditches and channels were connected to the tidal channels such that the higher elevated peat areas in the hinterland were drained and became habitable. The drained peat was also extracted at a large scale for industrial purposes. Thus the peat was used among others as fuel for cooking seawater or the purpose of salt production.

The draining of the peat resulted in subsidence causing the peat surface to get lowered. Also the extraction of peat contributed to the lowering of the peat surface. Due to the anthropogenic lowering of the surface the sea could enhance its hold on the peat area. This process was reinforced because of the fact that through the channels and the ditches the sea could penetrate the heartland of the peat areas where the surface was lowered artificially as well. The process of lowering of the peat surface occurred in particular during the second and third centuries of our era, due to the large- scale pear extractions which took place in those times in the peat areas of , the western parts of Zeeuws-Vlaanderen and Zuid-Beveland and Schouwen.

The consequences of these large-scale Roman extractions were disastrous. Because of the lowering of the surface major parts of the peat areas were flooded and the tide storage area increased considerably. In turn the tidal channels adjusted to the increased tide storage areas en increased strongly in size. Because of this the erosive force of the tidal channels increased and the peat near the tidal outlets was eroded away completely. In contrast to e.g. sand, peat gets largely lost for the sediment balance. Sand which is eroded remains largely in the tidal system and just shifts to different places. Peat, on the other hand, vanishes to a large extent because it contains a relatively large rate of water whereas the organic material decays. Thus the peat that is cleared through the tidal channels “vanishes” from the sediment balance system. This process of ‘’peat disappearing’’ led to a further increase in the tidal storage capacity and connected thereto a further expansion of the tidal channels. About 270 AD a self-reinforcing process of peat erosion, lowering of the surface, increase in tidal storage capacity and expansion of tidal channels came into being causing the Roman peat excavation areas to be completely submerged by 350 AD such that habitation and peat excavation in those areas had become impossible.

Because of the inundation of the peat areas and the enlargement of the tidal channels the coast of Zeeland had been breached completely. During the subsequent centuries, the sea could penetrate the peat areas in the hinterland even further. The process of drowning of peat eras continued there until about 800 AD when almost the whole of Zeeland was flooded

After 800 AD a change occurred in the coastal evolution. From those times onwards the natural sedimentation (deposits of clay and sand) began to outweigh the process of lowering of the peat surface again. Consequently, the tidal area which had come into being between the third and eighth centuries of our era started to gradually silt up again. The process of silting up led to the expansion of the salt marsh areas (which are called “schorren” in Zeeland). The silting-up process continued during the next centuries and as a consequence that the salt marshes which had risen by accretion were flooded less frequently. Around 1000 AD parts of the newly formed salt marshes even fell dry permanently and Flachsiedlungen were built on these highly elevated salt-marsh deposits. Investigations of mottes (châteaux à motte) in Zeeland have revealed that during the 11th century the Flachsiedlungen – which are located below the dwelling mounds – were elevated by soil such that about 1 m high dwelling mounds were formed. Obviously, during the 11th century the occupants were troubled more often by storm surges than during the 10th century.

7 1000 AD – present: Period of human influence

In the course of the 11th century man locally began to dike in parts of the salt marshes, e.g. Tubindic and Isenkike in Zeeuws Vlaanderen. However, the systematic, large-scale diking in of the salt marsh area in Zeeland took place during the 12th and 13th centuries. Around 1250 AD, the major part of the salt marsh area was already diked in. The embankments had far-reaching consequences for the landscape and the tidal processes in the areas that were not diked-in. Because of the embankments the seawater could not spread anymore over the salt marshes any more during storm surges. Since the storm waters did not have an outlet anymore, it was dammed up against the dikes and the storm surge level was raised. Before the 11th century - when no dikes existed - the water did not raise higher than 0.5 – 1.0 m above the then high silted-up salt-marsh surface but during the 14th century this level had raised to over 3 m above the local salt-marsh surface at the times of extreme floods.

By building sea walls in Zeeland man created a landscape situation which was favorable for the occurrence of flooding disasters. Not only the embankments of large parts of the salt-marsh areas had caused a significant rise of the maximum storm surge levels, but also the surface levels of the diked-in polder areas were lowered due to human interference. The most significant lowering of the surface level occurred in those polders where the soil consisted mainly of peat. The peat area s which were artificially drain by Man were extremely sensitive for subsidence. Also the clay excavations for the building of dikes and peat digging for salt production contributed to the artificial lowering of the surface. Due to the mentioned human actions, the difference between the maximum storm-surge level in the open sea branches and the lowered surface level in the reclaimed polders became several meters. When a dike breached, this had catastrophic consequences: the seawater streamed violently into the lower lying polders.

The flooding’s have led to long-lasting and even permanent loss of land in certain parts of the southwestern Netherlands. The area around the Braakman in the central part of Zeeuws Vlaanderen was inundated during the flooding’s of 1375/1376 and 1404 (St. Elisabeth Flood). It has taken 600 years for the area to be silted up sufficiently high such that it was reclaimed completely. Areas which have gone lost for a large part until present are the drowned Land of Zuid- Beveland and the drowned Land of Saeftinge. The drowned Land of Zuid- Beveland went lost during the St. Felix Flood in 1530 (St Felix quade saterdag) and the Drawing of the castle of Saeftinghe from 1505 storm surge of 1532. The lost of drowned Land of Saeftinghe was not cause by a storm catastrophe. During the military conflict between the Spanish troops and the Dutch army (siege of ) the dikes were cut deliberately by the Dutch in 1585 to stop the Spanish invasion to Antwerp.

The St. Felix Flood has had yet another important consequence for the landscape: it caused the Westerschelde to become the main outlet of the Scheldt River. Until 1530 AD the Oosterschelde had been the main connection between the Scheldt and the sea. The Westerschelde was navigable only during high tide because there was a bar between Saeftinghe and Bath. The shallowness at this place about 1500 AD was due to the fact that it was the location of a watershed where the tidal currents of the Westerschelde and the Oosterschelde met. The strength of the tidal currents in the watershed area was low. Therefore, the tidal channels in this zone were relatively shallow.

8 As a result of St. Felix Flood in 1530 AD - which resulted in the drowning of eastern part of Zuid- Beveland - the watershed between the floods coming from the Oosterschelde and Westerschelde shifted from the line Bath-Saeftinghe to the line Bath-Woensdrecht. As a consequence of this shift, the current velocity in the area between Bath and Woensdrecht in the Oosterschelde decreased markedly and the Oosterschelde tidal channel sited up there rapidly. As early as 1572 AD, on their advance towards Goes, the Spanish troops could wade through the Oosterschelde channel at low tide. During the subsequent centuries, because of the silting up, the area could be diked in in several stages. The tidal areas of the Westerschelde and Oosterschelde were definitive cut off from each other when the dike for the railway connection – Roosendaal was completed in 1867 AD.

Big flooding disasters such as the St. Felix Flood have occurred less frequently during the past few centuries, in particular due to the better quality of the dikes. The disaster of 1953 has taught us that the danger of flooding should never be underestimated and that necessary maintenance work and improvement of the dikes must be continued. If in the future a big flooding disaster would occur, the catastrophe (in terms of human and material losses) would, due to the considerable increase in the population in the Dutch coastal delta, even be much bigger than the one of 1953. Thus, it is best to assign the highest priority to the protection of the coast in the political decision-making process and to prevent the error from the past, when necessary maintenance was postponed for political and economic reasons.

References

Vos, P.C. & R.M. van Heeringen, 1997. Holocene geology and occupation history of the Province of Zeeland (SW Netherlands). In: M.M. Fischer (ed.), Holocene evolution of Zeeland (SW Netherlands). Meded. NITG-TNO, nr. 59, Haarlem, 5-109.

Vos P.C., 2002. Delta-2003, 5000 jaar terugblik, kaartatlas met toelichting. Landschapsreconstructie van de kustdelta van Zuidwest Nederland in opdracht van het project GEOMOD van het Rijksinstituut voor Kust en Zee (RIKZ) van het Ministerie van Verkeer en Waterstaat. TNO-rapport NITG 02-096-B.

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A cross section of the typical soil structure shows (from bottom to top): late Pleistocene cover sand, mid and late Holocene peat deposits and the medieval and post-medieval flooding sediments.

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The Drowned Land of Saeftinghe

The “Drowned Land of Saeftinghe” is one of the most important and largest salt marshes in Europe (3000 ha approximately). The landscape, consisting of of mudflats, shallows and salt marshes crisscrossed with water channels, is widely varied in flora and fauna. Its location on the sourthern rim of the Westerschelde estuary means that salty water from the North Sea mixes with the salt marsh channels turning them brackish. The area has a mean tidal range of 4.5 meters. Mean spring and neap tides are resp. 5.2 and 3.6 m.

Fauna and Flora

The plant life in the salt marshes reflects the impact of the brackish tidal waters. Scurvy grass is one of the many unusual plants you will find here along with other saltwater loving plants such as spear- leaved orache, sea purslane, sea aster, saltmarsh bulrush, sea arrow grass and sea couch. In the east, where the influence of freshwater is greater, you will find various reed beds that have evolved over the centuries.

Saeftinghe is also rich in birdlife. Thousands of coastal birds come to this area to breed, such as herring gulls, black-headed gulls, common terns and oystercatchers. The reeds are important brooding areas for species on the endangered list such as the bearded reedling, bluethroat, reed warbler and marsh harrier. In the latter part of summer sometimes more than 100 marsh harriers from the Delta area gather in Saeftinghe. In the course of autumn most migrate to the south and Saeftinghe is also an important port of call for many migrating and over-wintering birds. Of the geese species the greylag goose is the most prevalent with some 50,000 of them in the area at any one time. In addition the number of wigeons, shelducks, pintails and spoonbills is of international significance.

Legend

The legend of Saeftinghe is an old Dutch folk tale that explains the drowned city of Saeftinghe, tells how the Saeftinghe grew to be the most prosperous city on the fertile lands of the Scheldts but the inhabitants grew vain and proud. The farmers dressed in silk, their horses wearing silver and even the thresholds of homes were made from gold. The wealth attracted poor immigrants but the people of Saeftinghe showed no mercy and chased the migrants away with sticks and dogs. Greed corrupted the hearts of men and turned them blind for imminent threats.

On a foggy day, a fisherman caught a mermaid on the waters of the . From the nets, the mermaid warned him Saeftinghe needed to change its ways or suffer the inevitable dire consequences. When the mermaid's husband surfaced and asked for his wife to be set free, the fisherman refused and yelled at him. The merman cursed the fisherman and his city, screaming "The lands of Saeftinghe will fall, only its towers will continue to stand tall!"

The people of Saeftinghe, occupied with greed, forgot to take care of their dikes. One day, when a maid went to get water from a well, she noticed cod and other fish swimming in it. The sea was nearing, the water turning salt. With the All Saints' flood (1570), a huge tidal wave washed over the lands of Saeftinghe, destroying the towns of Sint-Laureys, Namen and Casuweel, killing all inhabitants.

Saeftinghe withered and soon only its towers testified of its prosperous past until the city finally sank into the muddy swamps. On foggy days, the tower bells call for help from what was once a wealthy place but is now a doomed world covered in mud, captured by the sea.

11 Holocene landscape evolution of Saeftinghe

During the early Holocene the area of the drowned Land of Saeftinghe was not yet covered by Holocene sediments. The Pleistocene cover sands were still exposed. The Saeftinghe area is located on a relative high Pleistocene sand ridge which had a northeast – southwest. The ridge separated the Zeeland tidal basis from the Scheldt river flood basin during the early Holocene.

The dry landscape conditions on the Pleistocene sand ridge changed between 5000 and 3000 BC. Due to the sea-level rise and infill of the Zeeland tidal basin, the groundwater seepage zone reached the area of Saeftinghe. Because of the high groundwater table the landscape became very Sand ridge landscape of NW Flanders and the southern Netherlands. wet. As a result peat growth It extends across the current Scheldt river trajectory started in the area. The peat growth on the Pleistocene ridge of Saeftinghe area continued for a long time because of its far inland location. It was consequently sheltered from the marine transgression which started after 270 AD in the western part of Zeeland. Around 800 AD, the tides of the sea gradually influenced the margins of the Saeftinghe peat area and clays were deposited in these margin areas. During the next centuries, the Westerschelde connection with the Oosterschelde became more and more prominent. From then onwards, the tides affected and influenced the whole area of Saeftinghe. The sedimentation of marine clay stopped in the area when Saeftinghe was diked in during the 12th and 13th century. Five villages were located in this area: Saeftinghe, Weele, Namen, St-Laureys and Casuweel. Because the subsurface consisted mainly of peat, the surface subsided significantly when man started to drain the clay-on-peat land by ditches. This lowering caused permanent loss of land after the military inundation in 1585. Due to the low lying surface, the tides flooded the area during every tidal cycle. Large tidal channels were created. The flooding of the area of Saeftinghe resulted in renewed clay sedimentation and elevation of the land. Parts of the lost land silted up and were diked in the next centuries after the inundation. The present day drowned Land of Saeftinghe is the last part of the in1585 inundated land which was never diked in again. The sedimentation still continues and this resulted in an enlargement of the salt marsh area between 1750 and 2000 AD. Because of the continued sedimentation the surface level of the salt-marsh areas of Saeftinghe are higher than the surface of the surrounding older polders.

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The Waasland Scheldt polders from the Late Middle Ages onward

Around 1000 AD the Northern Waasland area existed of a large swampy area, intersected by two embranchments of a Pleistocene sand ridge. In this swampy area we found extensive peat lands, which were excavated from the 12th century onward. Towns were located on top of the sandy ridge. By the end of the 16th century, almost the entire area was embanked but the large scale tactical inundations of the late 16th century resulted in an almost complete drowning of the area. A large tidal inlet developed as a consequence of this drowning. From the 16th to the 20th century, the area was re-embanked, mainly under the influence of rich citizens and nobility. The present day “Land van Saeftinghe” is the only reminder of the former tidal marsh.

th I. Jongepier End 16 C. 1654 1688

1784 1846 19th C. Saeftinghe

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Evolution of the (natural and man-made) landscape of the Land of Saeftinghe

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Google Earth image (2013) of the Drowned Land of Saeftinghe with the probably location of the villages of Saeftinghe (by approximation)

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Saefti ghe

Map of the 'Land of Saeftinghe' from 1575

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Map of the area at the end of the 16th century

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