SEA LEVEL RISE, TRANSGRESSION PHASES AND STORM SURGES IN MARITIME FLANDERS TO THE END OF THE 16th CENTURY. A STUDY OF THE LANDSCAPE, ECOLOGY AND CLIMATE FROM A HISTORICAL POINT OF VIEW1

Dr. Beatrijs AUGUSTYN GENERAL CONCLUSION The object of this dissertation is to extend the debate on sea level changes, transgression phases and storm tides via historical research. Consequently, three elements were examined:

1. The influence of long-term movements of the sea level on the coastal plain in historical times. In other words, we reopen, via the historical way, the discussion whether the sea level has risen or not since the Subatlanticum (which is shortly before our era).

2. The influence of the half-long-term movements of the sea, the so-called transgression and regression phases which are supposedly cyclical periods of rises and falls of the sea level or eras of increased or decreased influence of the sea on the land.

3. Finally, the consequences of the factor storm tides of which, according to some, frequency and intensity in historical times are closely connected with the half-long-term movements of the sea level

This study was undertaken as a result of the interdisciplinary colloquium organized in Ghent in 1978 about “Transgressions and the history of the settlement in the coastal areas of Holland and Belgium” which focused on the extent in which geologists and soil scientists require purposive landscape research about the Northwest European plain in order to be able to solve the fundamental problem which rises in connection with the discussion of the sea level rise in historical times. This problem is part of the controversy between the actual inductive research into the rising of the sea level which, following Jelgersma’s curve from 1961, excludes a noticeable rise of the sea level since the beginning of the Subatlanticum, on the one hand, and the transgression phase theory developed by means of deduction, still very much alive today, which stands for climatologically determined cyclical phases of strong sea level rises in historical times, on the other hand. In imitation of the Dutch soil scientist Bennema, the adherents of the second theory accept that a new Subatlantic transgression phase started in 1870 which will continue until after the year 2100 expressing itself through a “physical sea level rise” of 15 cm per century. Possibly anthropogenic factors for the rise of the sea level, which have been recorded by several meteorological coastal stations in the Netherlands since the end of the 19th century, have been rejected by them. Our treatise consists of 5 parts.

1 English summary of the general conclusion of the thesis by B. AUGUSTYN, Zeespiegelrijzing, transgressiefasen en stormvloeden in maritiem Vlaanderen tot het einde van de XVIde eeuw. Een landschappelijke, ecologische en klimatologische studie in historisch perspektief, Brussel, Algemeen Rijksarchief, Studia 37-38, 1992 (reprint 2000).

The first part inevitably had to be made up of a critical analysis of the literature. We particularly wanted to explain how the current Dutch sea level curves, drawn up at the State Geological Service by Jelgersma and Van de Plassche, who enjoy world-wide recognition for their inductive method, the severe selection criteria of the index points at the basis of the peat layer and the statistic processing of them, have brushed aside all earlier sea level curves including those of Bennema and Roeleveld. Examining the Belgian literature with respect to soil science, we feel it is important that we have been able to show that the transgression phase theory finds its origin in an axiom formulated by Raoul Blanchard in his thesis “La Flandre” of 1906. We suppose that only few people still realize that he “designed” Dunkirk-II-transgression phase and that he imagined our coastal plain to be transformed into an area with “wadden flamands” in post-Roman times, in the course of which the Older Dunes were swallowed up by the sea. In 1948, when the “Soil map of Belgium” was drawn up, this “wadden phase” was split up into the three Dunkirk transgression phases. This has left its mark on Northwest European soil survey with respect to the dating of clay layers. The meteorological phenomenon of storm tides obviously got ample attention as well. We drew attention to the extent to which the present knowledge, with respect to past storm surges, is the result of the research of the late mrs. Gottschalk who, in the margin of the sea level research, collected all available historical information concerning storm surges and the damage they caused in the Netherlands, North Germany and Flanders. Her research led her to draw two conclusions which we consider to be of fundamental importance. As a result of her conclusion that storm tides never swept the entire Dutch coast but sometimes the south, at other times the north, she put that there are no indications in the historical archives authorizing the use of the notion sea transgression phases. Consequently, she felt that maritime deposits in historical times should only be interpreted regionally. Our findings confirm this point of view. Nevertheless, we do not entirely agree with the purely climatological interpretation of her basic criterium, the size of the damage, which led her to place a peak storm tide intensity in the 16th century. We feel that political and economical factors can be set against this view. Before the establishment of the meteorological institutes in the 19th century, a calculation of the frequency of storm tides remains also impossible according to us. In the second part we have tried to fit our research into the study of sea level rises and transgression phases by collecting and analyzing the information about the rises of sea walls and flood levels at the Wester Scheldt estuary. In our opinion, the historical documentation material about the height of the dikes along of the Wester Scheldt in Zealand Flanders from the beginning of the 13th century until the end of the 16th century, is unique for the whole of the Northwest European Plain. Furthermore, these data allowed by their remarkable precision, such as the determination of the height with respect to the tidal level as well as to the ground level, for statistical comparison with sea dike heights from the 20th century at this estuary. Due to this we could show that the sea walls of the Wester Scheldt, laid out since the Reclamation period (from the 12th to the 13th century) were probably no

lower than the dikes at the eve of the storm tide disaster of 1953, which casts doubt on a considerable raising of the sea level since the 12th and 13th centuries. In this research we were only confronted once with a real heightening of the sea walls. After the storm surge of 1424, the sea dikes of the Land of Saaftinge and the Land of Beveren on the southeast Wester Scheldt bank were raised from 14 to 18 feet at the sovereign’s command. 15th century trials concerning the Wester Scheldt as a shipping route include hydrographic information which we analyzed in connection with the study of the heights of the sea walls. They show that the raising of the sea dikes by one meter can not be attributed to an escalating storm tide intensity during the so-called “late-medieval sea transgression phase”, but has to be connected with higher flood levels along the Flemish banks of the south-eastern part of the Wester Scheldt as a result of hydrographical changes which came about in these parts. The river channel had shifted to the Femish bank and, furthermore, had become wider and deeper as a result of coastal erosion and the widening of the estuary of this seagate. The current flow and the rate of flow increased which in turn caused the flood level to rise. A scunding report of the Wester Scheldt estuary of 1549 provided supplementary confirmation. In addition, parallels could be found in the manuscript of the 16th century “waterstaat” expert, Andries Vierling (an expert on dikes) who mentioned only anthropogenic and no physical-climatological nor physical-geographical factors for the flood level rise and the widening of the Zealand estuaries. In a third part we tried to fit our study within the broader framework of the dune erosion and the withdrawal of the Flemish coast in historical times and the possible anthropogenic factors of this phenomenon, because we felt this could also provide us with information about the three “Dunkirk-transgressions” and the supposed “wadden-phases” associated with them. At the same time, we verified what was true of Blanchard’s interpretation of the land along the Flemish coast swallowed up by the sea during the late Middle-Ages, a phenomenon which he attributed to a regularisation mechanism which is supposed to be typical for sandy coasts. This theory indeed continues to live on in the literature on soil science. From the very beginning of this study based on texts, it appeared that on the eve of the great Reclamation Period, the so-called Older Dunes – of which actually local leftovers were recently found also along the east coast of Belgium, and not only along the west coast – were probably still virtually intact, forming a stable sea wall for the salt marshes and peat moors lying behind them. The destabilization of the Older Dunes probably only started during the Reclamation Period especially from the 12th century onwards. This was no direct consequence of physical-climatological causes such as the rise of the sea level nor from ground mechanical coast regulating phenomena, but of human interference in this natural environment. From the 12th century onwards, the count of Flanders was able to turn the dunes into a profit as a result of the changed political-economical structures and a population increase. This happened at the cost of the protective function of this natural sea wall. During the construction of the ports of Calais, Gravelines, Dunkirk an Nieuport in the 12th century and Ostend and Blankenberge in the 13th century, the Older Dunes were locally flattened and their forests cleared. This did not remain without consequences. Ostend and Blankenberge were swept by storm tides and partly given up to the sea no later than one century after their construction.

An intervention which proved to be even more dangerous in the long run and one which would finally lead to the total destruction of this eco-system at the end of the 14th and the beginning of the 15th century, was the general reclamation of the Older Dune area turning it into pastureland for cattle, horses and sheep and hunting grounds, to replace the embanked salt marshes and the cleared forests of Inner-Flanders. This led to a real deforestation of the Older Dunes. It is remarkable that after the Ghent Revolt (1379-1385), during which the dune regulations appear to have been violated in all respects, mention is made for the first time in historical sources of a not to be stopped land inward “vloge van den zande” (sand drift). A catastrophe could not longer be avoided. The storm tide of 1404 turned out to be the final blow. The Older Dune massif almost completely disappeared except for a strip along the west coast. The beach embankments on which the dunes rested were to a large extent swallowed up by the sea and a large number of taxable polders had to be crossed off the lists of apportionment for the direct taxes, the so-called Transport of Flanders. The coast erosion was obviously worst at the estuary of the Wester Scheldt. Wulpen, a flourishing island before Cadzand, disappeared for ever in the waves with its five parishes and the small port of Waterdunen. This also caused the major silting up of the Zwin, the waterway to Bruges, shortening its estuary by many kilometres. The Younger Dunes as we know them at present, with their unstable and almost bare dune peaks still subject to sand drifts and moves, only came into being in the late Middle-Ages, at the end of the 14th, beginning of the 15th century, as a consequence of anthropogenic factors which destroyed the Older Dune massif. These Older Dunes were not swept away by successive transgression phases since the beginning of the Subatlanticum. This also means that no longer can any credit be attached to the three Dunkirk-wadden-phases. This view is in keeping with the examination of the dunes executed by the Dutch State Geological Department. Behind such a broad and high Older Dune belt, the vegetation of the high moorland which is sphagnum peat rising above the sea level and fed by rainwater since the beginning of the Subatlanticum, can no longer be a problem in maritime Flanders. In the past we were already confronted with criticism on the reaserch carried out previously in connection with the peat digging in the Noth Flemish high moors not covered by marine clays. This criticism was connected to faulty notions which we were able to counter within the framework of this study. According to a number of Belgian soil scientists, moorland vegetation in areas close to the coast would have been impossible as a consequence of the supposedly progressing sea level rises because the groundwater level would have risen as well preventing all moorland vegetation. The supposed Dunkirk transgressions would, according to these scientists, have covered most of the coastal plain and the area of the Wester Scheldt with clay during Dunkirk I or at latest during Dunkirk II. As we were able to refute this view, moorland vegetation was possible as well as a large scale exploitation of this outcropping moorland. Renewed study in the fourth part of our thesis of the richly documented micro-region, the Land of Beveren, does not leave one in any doubt. We studied the foundation of

the moorland colonies Kieldrecht and Verrebroek and were able to compare them to the 16th century Dutch colony Veenendaal in Gelderland. We proved that in the period of the Great Reclamations peat digging in North Flanders took an ‘industrial’ shape because of the increased need for fuel in the quickly developing cities within the county of Flanders and as a consequence of the clearing of the forests lost in this way for fuel consumption. In the spongy moorlands complex and expensive infrastructure works were necessary before the peat could be exploited. This required a thorough knowledge of hydraulic engineering. The draining was regulated via a complex system of dikes, sluices, canals and wooden drainpipes. The high cost of fuel forced up the value of the peat enormously so that embanking the salt marshes was imposed by the authorities by means of sanctions set down in the dike laws. In this way, the moors in North Flanders were protected against storm tides by sea dike lines. At the same time, we opposed Hendrik Van der Linden’s “Cope” theory of 1956 which still dominates the historical-geographical research in the Netherlands. He put that the cultivation of the Holland-Utrecht peat moors happened during a period with climatologically favourable circumstances and a lower sea level (before the so-called late-medieval transgression phase) in which the moorlands are said to have become drier as a result of natural causes and could be cultivated as farming land without hydraulic infrastructure works. Van der Linden rejected what he called the “compulsion to embank” as had been accepted previously by Fockema Andreae. To prouve our point of view in this matter we devoted our attention in a fifth part to the formation of fenland meres. We feel that the history of their origin has been strongly influenced by the “Cope” theory: when the Holland-Utrecht moors were supposedly cultivated without a refined drainage system consisting of dikes, dams and sluices, uncontrolled drainage must have led to a differentiated peat soil compaction resulting in the formation of lakes not long after the cultivation started. By means of a case-study of the reclaimed lake “De Lage Moere” of Meetkerke close to Bruges, we have tried to show that intensive peat digging, followed by peat dredging below groundwater level lies at the basis of the existence of this lake. However, this does not imply that we consider the factor peat soil compaction to be of no importance. As the research into the Land of Beveren points to a good knowledge of water level control in the moors since the period of the Great Reclamations, we considered the phenomenon of peat soil compaction to be of limited importance before the period in which water control regulations were violated, economic motives being the reason. According to us, this happened at the earliest from the end of the fifteenth century onwards when the peat dredging started and the hydraulic infrastructure was neglected and finally dismantled. The uncontrolled peat exploitation undoubtedly stimulated the compaction of the soil which helped to bring about the existence of extensive linked fenland meres. To conclude we can put that we have tried to work out via four different ways to what extent transgression phases and the rising of sea level have influenced the maritime history of Flanders. Our temporary conclusion is that there are no indications for the existence of transgression phases nor for the rise of the sea level in historical times. Human activities seem to have played a part in the destruction of the ecosystems

studied, the dune belt and the zones of moorland in Flanders. In our opinion, a precise chronology of the diking in the coastal plain could in future teach us a lot about the clay layers of maritime Flanders which in large part were probably only deposited at a later date than many publications lead us to believe now. The research we have carried out permits us to formulate findings which transcend the span of our study. Indeed should the late medieval climatological optimum (annex transgression phase) be no longer valid, then the Little Ice Age will de facto fall of its pedestal. In that case the known general melting away of the glacier massives in the Northern part of the Hemisphere since the late 19th century, the slow temperature rises recorded since that time in the meteorological stations in Western Europe and the East of the United States and the rise of the sea level measured at the coastal stations in the Netherlands can no longer be attributed to climatic changes, but these phenomena must then be viewed against the light of the Industrial Age, a view shared at present by many climatologists. The existence of a current climatologically determined sea transgression phase rests on a theory developed by Bennema after the storm tide disaster of 1953 which heavily ravaged the Netherlands, but the theory remains unproven. Our study of the dunes and the high moorlands also opens new perspectives for the historical-geographical research into the Northwest European Lowland and will, we hope, permit a better evaluation of historical landscape relicts. We think to have shown convincingly to what extent the Dunkirk transgression phase theory has had a restraining effect on the research of the landscapes of the areas close to the coast by postulating repeated phases of total land destruction in the period preceding the diking in movement. Differential development of the coastal landscape can be considered if the historical geography of the coastal plain can be separated from the narrow chronological framework of the physical-deterministic theory, and anthropogenic factors are put forward instead. Our vision was also influenced by the essay of the Amsterdam professor G. Borger “De bedreiger bedreigd” (The intimidator intimidated), whose thoughts concerning the interaction between anthropogenic and natural processes, in our opinion, are directional for future climatological and landscape ecological investigations of coastal regions. In the essay he puts that “any attempt to picture the interrelated dependence in the relation man-nature as straightforward and predictable is questionable” and “that regional processes active in landscape development and specifically man as a landscape shaping factor explain much better a number of such phenomena” (especially the fluctuations of the sea level). With our research we associate ourselves with the ecological vision of the English “post-modern” historical-geographical school of A. Baker which sees man as the motor of landscape changes and for that reason stresses “areal differences” and goes much less in search of “spatial regularities”. We hope, even though we had to limit ourselves to test regions and purposive problems because of the abundance of sources and the ample issues, that our empirical examination of the literature and the sources will lead specifically to two results.

Firstly, that those who have read our thesis will understand that to date the research of the coast has been hampered by too many insufficiently argued axioms. Secondly, that a renewed interdisciplinary debate about these problems will start up in which historical investigation will be assessed at its value.