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The Seine River from Ile-de-France to Normandy: Geomorphological and Cultural Landscapes of a Large Meandering Valley Jean-Pierre Peulvast, François Bétard, and Christian Giusti

Abstract

Rich in historical and cultural heritages, the stretch of the Seine valley that links Île-deFrance to Normandy, between Mantes-la-Jolie and the Eure and Andelle confluence zone, belongs to one of the major sets of entrenched meanders known in the world. The valley presents steep hillsides punctuated by white chalk pinnacles alternating with deep funnels, contributing to the picturesque landscape of the valley segment. The geomorphic history of the Seine valley is inseparable of the Quaternary bioclimatic history, with its alternating glacial-interglacial and stadial-interstadial periods. All along the Pleistocene, periglacial processes interacted with fluvial erosion, leading to the formation, deepening, enlargement, and migration of the large meanders. The resulting, present-day geomorphological landscapes are enriched by many cultural treasures. Its emblematic sites are the medieval castles of La Roche-Guyon and Les Andelys (Château-Gaillard) which were built on rocky promontories on the concave sides of two large meanders. The mid-Seine valley is also known as a high place of the impressionism, the founder and master of which, Claude Monet, settled here for the second half of his life and created the wonderful gardens of Giverny on the lower Epte River. He and many other impressionist and postimpressionist painters, sensitive to a certain harmony of the local landforms, magnified and immortalized the surrounding landscapes. Keywords

Meanders • Chalk erosion • Periglacial features • Impressionism • Castles

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J.-P. Peulvast (*) Geomorphology, University of Paris-Sorbonne, Paris, France e-mail: [email protected] F. Bétard Physical Geography, Paris-Diderot University, Paris, France e-mail: [email protected] C. Giusti Physical Geography and Environmental Sciences, University of Paris-Sorbonne, Paris, France e-mail: [email protected]

Introduction

Among the regions of France where remarkable geomorphological landscapes also represent invaluable historical and cultural heritages, the stretch of the Seine valley that links Île-de-France to Normandy, between Mantes-la-Jolie and the Eure and Andelle confluence zone, is one of the most present in the collective memory. Due to moderate heights, it does not display the most spectacular landforms in any specific geomorphic type, although it belongs to one of the major sets of entrenched meanders known in the world. It rather owes its fame to events and constructions linked to its position on the most active way linking Paris to the sea and on the historical border of Normandy, as well as to the numerous literary and pictorial representations of its landscapes. The valley

M. Fort and M.-F. André (eds.), Landscapes and Landforms of France, World Geomorphological Landscapes, DOI 10.1007/978-94-007-7022-5_3, © Springer Science+Business Media Dordrecht 2014

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Fig. 3.1 Vétheuil (in the background, right side) and the concave side of the Moisson meander of the Seine valley, from Haute-Isle (Photo J.P. Peulvast, January 1982). Only the lower half of the slope is shaped into

the Campanian chalk (pinnacles), whereas the upper half corresponds to Cenozoic layers. A winter flood underlines some lateral channels outside the main one (island on the right side)

presents steep sides punctuated by white chalk pinnacles and pierced by caves and troglodyte dwellings (Fig. 3.1). Its emblematic sites are the castles of La Roche-Guyon and Les Andelys (Château-Gaillard), ancient lookouts on the Seine valley, the latter having been harshly disputed in the thirteenth century between the Duke of Normandy and King of England, Richard the Lionheart, followed by John Lackland, and the King of France, Philippe August. But the mid-Seine valley is also known as a high place of the impressionism, the founder and master of which, Claude Monet, settled here for the second half of his life and created the wonderful gardens of Giverny on the lower Epte River. He and many other impressionist and postimpressionist painters magnified and immortalized the surrounding landscapes. Beyond the quality of the light, all these artists were sensitive to a certain harmony of the local landforms. A more scientific approach helps in understanding the layout of these landforms and discovering a rich geomorphological heritage which contributed to justify the preservation of part of them in the “Parc naturel régional du Vexin Français.”

right side, marks the entrance of the valley in Normandy (Fig. 3.2a). Upstream, the Seine River separates the Vexin Français (north), from the Mantois region (south); both units belong to the same plateau area. Whereas the Seine River flows to NW, from 19 to 8 m a.s.l. downstream of Les Andelys, this plateau largely dedicated to farming gently slopes to southeast, from 150 to 160 m in the tabular Vexin Normand to 120–140 m around Mantes-la-Jolie. Therefore, increasing heights (up to 140 m) characterize the valley sides. More and more spectacular downstream, they form outstanding historic and touristic sites (Château-Gaillard, Côte-des-Deux-Amants; Fig. 3.3a, b). In the Vexin Français, north of Mantes-la-Jolie, narrow WNW-ESE alignments of wooded buttes overlook the plateau close to the valley, reaching 206 m a.s.l. near Vétheuil (Fig. 3.2a). The valley floor is generally wide (1–2 km), although it locally narrows to 600 m, between Giverny and Vernon. However, the presence of a few confluence zones and, above all, the meandering outlines of the main valley explain considerable variations in width as well as strong asymmetries in the valley sides. Left-side tributaries remain scarce and short down to the wide confluence plain of the Eure River (Fig. 3.2a). Downstream of the narrow Vaucouleurs valley, which cuts through the low fluvial terrace forming the urban site of Mantes-la-Jolie, a few deep and mostly dry valleys only incise the rim of the otherwise weakly dissected plateau. On the right side, short tributaries also dissect the rims of the Vexin Français and Vexin Normand. Only some of them are drained by permanent creeks, in their downstream reaches.

3.2

Geographical Setting

Sheltering two important cities, Mantes-la-Jolie and Vernon, the studied segment of the Seine valley crosses the border between Île-de-France and Normandy 50–100 km downstream from Paris. It includes two sets of large meanders separated by a 20 km long rectilinear segment, from Vernon to Gaillon. The confluence zone of the Epte River, on the

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The Seine River from Ile-de-France to Normandy: Geomorphological and Cultural Landscapes of a Large Meandering Valley

Fig. 3.2 The Seine valley and its surroundings between Mantes-la-Jolie and the Eure-Andelle confluence zone. (a) 3D representation, from SRTM DEM (F. Bétard). Note the importance of large enclosed depressions on the valley floor, mainly downstream of Mantes-la-Jolie: active

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and former sand pits. (b) The Gaillon-Les Andelys meander. Note the chalk pinnacles around Les Andelys (the small city on the right side), the large sand pits in the alluvial plain and the Port-Mort dam and lock. Red strip: the abandoned meander of Daubeuf (Photo J.P. Peulvast)

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Fig. 3.3 The concave side of the Les Andelys and Poses meanders at les Andelys, from Château-Gaillard (a) and at Amfreville-sous-les-Monts, from the Côte-des-Deux-Amants (b) (Photos J.P. Peulvast). Inherited periglacial landforms (Richter slopes, chalk pinnacles) overlooking a narrow “modern” alluvial plain

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The Seine River from Ile-de-France to Normandy: Geomorphological and Cultural Landscapes of a Large Meandering Valley

However, two bigger rivers coming from the humid Pays de Bray, to the north, form wider confluence zones. The lower Epte valley, a well-calibrated fluvial trough, only widens at Giverny, separated from the Seine valley on its last 5 km by an elongated plateau strip reduced to a low crest near La Roche-Guyon. On the contrary, the lower Andelle valley, also turning from SSW to WSW, directly opens on the 3–4 km wide Seine-Eure confluence zone at Pîtres, below a protruding spur named Côte-des-Deux-Amants. The sinuous parts of the valley, with wavelengths of 4–5 km, classically display low convex and asymmetric lobes gently sloping to the downstream side, opposite to high, abrupt, and partly rocky slopes sharply cut into the concave sides, either directly into the plateau or into the upstream side of the inner lobes. The most of these convex lobes are elongated perpendicularly to the general trend of the valley, over 6–7 km. With altitude decreasing from 80 to 90 m to the floor, they entirely belong to the valley domain, the total width of which is therefore highly variable. Moreover, blunt hillsides with concave outlines, disconnected from the river, draw ancient contours of meanders which later migrated downstream, also contributing to increase the total width of the valley, up to 2 (Vernon, Port-Mort) to 4 km (BuchelayMantes-la-Jolie, Gaillon) or even 6 km (abandoned meander of Daubeuf, west of Les Andelys) (Fig. 3.2b).

3.3

Geology

Downstream of Mantes-la-Jolie, picturesque outcrops of Cretaceous chalk form an increasing proportion of the valley-side profiles (Fig. 3.3). Unique among landforms usually covered by soils and superficial deposits, they announce the white vertical cliffs of the Normandy coast and reinforce the scientific interest of landscapes which may be considered as potential geomorphosites (Reynard et al. 2009). They reflect the entrenchment of the Seine valley into the oldest of the layers that form this part of the Paris Basin, to the west and northwest of the Cenozoic plateaus of Île-de-France. After a long period of emersion since the end of the Jurassic, a marine transgression occurred in the Paris Basin in mid-Cretaceous times (Aptian-Albian). This was the beginning of a long sequence of high sea levels during which carbonate sediments were deposited on vast regions, in warm and shallow water. Hundreds of meters of chalk layers were deposited over large parts of northwestern Europe. Here, the last of them were deposited in the Campanian (83–70 million years), after which the basin progressively emerged and was submitted to erosion. Older chalk layers (Santonian, Coniacian, Turonian) outcrop in the lower parts of the valley slopes, downstream of Bonnières and mainly on the right side. All of them generally contain more or less regularly spaced flint layers and nodules which contribute to increase their relative resistance to weathering and slumping. This

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resistance allows the formation and preservation of steep cliffs along rivers and shores. The Cenozoic sediments that overlay the Late Cretaceous chalk are only represented to the southeast (Vexin Français) and to the south, between the Seine and Eure valleys. Paleocene sediments are absent, except in tiny depressions where reefal and peri-reefal limestones are preserved along paleo-fault scarps (Vigny). In the Eocene and Oligocene, the sea invaded periodically the center of the Paris Basin from the English Channel, along a low Seine corridor limited to the north by the NW-SE Bray antiform. After a lacustrine phase in the Ypresian (Sparnacian clays), the last important layer of Lutetian marine limestone (“calcaire grossier”) was deposited in a large bay. It presently forms structural surfaces in the Vexin Français and south of the Seine River. Continued by lacustrine and lagoonal sand, marl, and limestone locally interbedded with gypsum and silcretes of Late Eocene age, this series was finally covered by thick littoral sand layers deposited in the old marine corridor and in the Fontainebleau gulf, capped by thin lacustrine silicified clay (“meulière”) closing the sedimentary cycle in ChattianAquitanian times. The later erosion of this series was induced by shallow inversion of the basin, accompanied by the progressive formation and incision of a paleo-Loire-Seine drainage axis oriented to the Channel along NW-SE structures (Seine fault, shallow synforms and antiforms). Leading to the formation of the surface that presently forms the main plateau, this phase of denudation resulted in partial erosion of the upper layers of the Cenozoic series. It only preserved the narrow buttes of Oligocene sand capped by hard silcrete (“meulière”), which form the remote frame of the valley in the Vexin Français and Mantois regions (Fig. 3.4). Before the PlioQuaternary dissection, these buttes were overlooking a large plain where structural surfaces shaped into the Cenozoic limestone layers merged to the west (Vexin Normand) with the exhumed sub-Eocene erosion surface cut into the chalk layers (Dewolf 1982). Reworked until the Pliocene, this surface corresponds to the “flint clay surface” identified in Normandy. Pockets of reddish flint clay are visible under this surface, in quarry walls around Vernon (Fig. 3.5a). They indicate the contribution of subsurface karstic processes to its shaping and the preservation of weathering products in depressions and pits formed by dissolution.

3.4

Landforms and Quaternary Evolution

The landscapes of the Seine valley were formed during the incision phase that followed the last planation stages, the age of which is given by alluvial deposits of the paleo-LoireSeine preserved on the plateau and known as “sables de Lozère” or granitic sands – i.e., produced by weathering of granitic gravels transported from the Massif Central. The

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Fig. 3.4 Geological profile of the Seine valley and southern Vexin Français between Vétheuil and La Roche-Guyon (From Pomerol and Feugueur (1974), modified). mi silcrete (“meulière de Montmorency”), Chattian; mii Fontainebleau sand, Stampian (Rupelian); m marl and green clay,

“Sannoisian” (Early Rupelian); e3 marl, “Ludian” (Priabonian); e1 Beauchamp sand (Bartonian); eii−i limestone (“calcaire grossier”), Lutetian; eiii Cuise sand (Ypresian); eiv plastic clay, “Sparnacian” (early Ypresian); c8 white chalk, Campanian; c7 white chalk, Santonian-Coniacian

Pliocene to Early Pleistocene (Gelasian) age of these sands is established from outcrops in the region of Fécamp, close to the English Channel coast, which also registered a regional uplift of 60–100 m since that time (Quesnel et al. 2003). Combined with lowering sea levels and repeated Quaternary episodes of emersion of the Channel, this uplift determined the incision of the lower Seine valley in the former plain. Although deprived of part of its water by the diversion of the Loire River to the Atlantic in the Early Pleistocene, the Seine River maintained its former direction, but its incision in a slowly uplifting region was accompanied by the formation of large meanders progressively entrenched into the plateau. This history is inseparable of its bioclimatic context, with the alternating glacial-interglacial and stadial-interstadial periods of the last 2.6 million years, succeeding to warmer Pliocene conditions. Like the rest of Western Europe, the region suffered increasingly severe, long, and frequent periods of periglacial climate during the Pleistocene, especially in the last 700,000 years and until the end of the Younger Dryas, 11,500 years ago. In such cold and mostly dry conditions, with continuous permafrost blocking water infiltration, rock disintegration was more efficient than dissolution in carbonate rocks, especially in the chalk, which suffered deep frost shattering. Mass wasting was efficient in steep slopes formed by fluvial sapping and submitted to processes such as rock falls, solifluction, debris flows, or superficial runoff (Fig. 3.5b). Large quantities of waste were provided to the Seine River which, under periglacial climates, carried and deposited thick

layers of sand and gravels. These alluvial deposits often contain huge blocks (“blocs démesurés”) of sandstone or limestone transported on ice floes during powerful flows triggered by seasonal thawing of snow and fluvial ice. Also efficient in the affluent valleys, owing to impermeability of the frozen bedrock, these processes interacted with fluvial erosion all along the Pleistocene, leading to the formation, deepening, exaggeration, and migration of the large meanders. In a magisterial study of the Quaternary geology in the middle course of the Seine valley, F. Lécolle (1986) described the alluvial deposits preserved in the form of wide glacis on the lower parts of the convex lobes of the meanders and the original type of evolution that characterized this segment deprived of true fluvial terraces (Fig. 3.6a). The system of meanders evolved both by continuous deepening and by progressive lateral migration of the river, leading to the formation of “conservative meanders.” From a detailed study of the large sand pits opened in the alluvial cover of the convex lobes down to the modern alluvial plain, F. Lécolle evidenced series of 100 m wide stepped terraces shaped into the bedrock and separated from each other by scarps of 1–2 m (Fig. 3.6b). Each step bears oblique and partly embedded sets of deposits defined as “alluvial nappes,” the lower and upper limits of which are those of the major erosion phases which shaped the bedrock steps or paleochannels (Fig. 3.6b). In the meanders of Guernes and Moisson, 16 of them were identified, corresponding to Mid- and Late-Pleistocene sequences of Late Elsterian to

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The Seine River from Ile-de-France to Normandy: Geomorphological and Cultural Landscapes of a Large Meandering Valley

Fig. 3.5 Weathering mantle and superficial deposits on the Seine valley sides (Photos J.P. Peulvast). (a) Karstic pits and flint clay at the edge of the Vexin Normand plateau above Sainte-Geneviève-lès-Gasny. (b) Stratified talus over longitudinal debris flow deposit and frost-shattered

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chalk and flints at the mouth of a short periglacial gully incised in the lower Epte valley side between Sainte-Geneviève-les-Gasny and Giverny. Legend: 1 Frost-shattered chalk, 2 Longitudinal debris flow deposit, 3 Lateral colluvial deposit

Fig. 3.6 Meanders and alluvial deposits in the Seine valley between Mantes-la-Jolie and Freneuse. Slightly modified from F. Lécolle (1986). (a) Map of the alluvial deposits and paleochannels showing the downstream migration of the entrenched meanders of Guernes and Moisson. Legend: 1 Altitude, 2 Limit of the Mantes-la-Jolie agglomeration, 3 Sand or gravel pit, 4 Holocene deposits, 5 Early and mid-Weichselian deposits, 6 Saalian deposits, 7 Elsterian deposits, 8 High level terrace

(Elsterian ?), 9 Loess, 10 Pre-Quaternary bedrock. I, II, III, IV: numbers of the alluvial “nappes” (see b). (b) Profile of the alluvial nappes and paleochannels in the Guernes meander. Note the oblique pattern corresponding to the lateral migration accompanying the progressive incision and the lack of fluvial terraces. Legend: 1 Chalk; 2 Ice-transported block; 3 Pebbles, gravel, sand, 4 Frost-shattered pebbles; 5 Sand; 6 Silt; 7 Fluvial clay, 8 Soil, with pedogenetic reddening; 9 Cryoturbation features

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The Seine River from Ile-de-France to Normandy: Geomorphological and Cultural Landscapes of a Large Meandering Valley

Mid-Weichselian ages, as determined from their degree of weathering and cryoturbation as well as from their fossil fauna and their prehistoric industries. A large part of these deposits reflect catastrophic sedimentation events in cold, periglacial conditions with strong seasonal contrasts. Erosive stages might correspond to the beginning of milder periods with liberation of water giving to the river an increased transport capacity. Their disposition, their superficial truncation by wide glacis, as well as the preservation of stepped paleochannels on the convex side of the valley floor result from simultaneous lateral migration of the river and vertical erosion in the meandering segments. This migration both reflects an exaggeration of the sinuosity and a downstream migration of the valley meanders (Fig. 3.6a). On convex lobes as well as on all concave sides of the meanders, a narrow strip of modern alluvial deposits separates the hill slopes from the river. Spectacular chalk pinnacles alternating with steep funnels and rectilinear slopes ornate the right side of the valley in the meanders of Moisson, Les Andelys, and Poses. Capped in the southeast (Limay, Vétheuil) by a short cornice of Lutetian limestone which slightly receded by sliding over the Sparnacian clay (Figs. 3.1 and 3.4), these hillsides bear the marks of periglacial processes. Rectilinear profiles (Richter slopes) are well-developed downstream of Les Andelys (Côte-des-Deux-Amants; Fig. 3.3b) and on concave segments of the left side, face to the north (Bonnières-Port-Villez). Their contact with the alluvial plain is sharp, reflecting the scarcity of talus deposits. With their alternate layers of fine gravel and bigger debris, these “grèzes” reflect the variable efficiency of frost shattering in the Late-Pleistocene cold stages and the redistribution of

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fine-grained material by superficial solifluction. Another type of deposit was observed at the bottom of one of the regularly spaced funnels that separate the pinnacles, east of Giverny. Here, thick layers of heterometric material reflect transport and accumulation processes involving debris flows along the talweg (Fig. 3.5b). This might confirm the suggestion of C. Pomerol (Pomerol and Feugueur 1974) that seasonal thawing of snow patches and of the permafrost active layer might have activated combined processes of gully incision and mass wasting in slopes exposed to SW, S, and SE.

3.5

Landscapes: Human Impact, Cultural Perspectives, and Preservation

The most famous sites of this region result from historic valorization of the steepest hillslopes and pinnacles on the right side of the valley. The medieval castles of La Roche-Guyon and Château-Gaillard were built on rocky promontories of the concave sides of the Moisson and Les Andelys meanders, opposite to large convex lobes, offering excellent views on the river and some of the widest panoramas over the valley (Fig. 3.7). Although largely destroyed after being won by Philippe August in 1203, the Château-Gaillard still presents imposing remains, including an enormous keep, of a fortress which had been built at the top of a narrow chalk promontory, over the confluence zone of the Cambon and Seine Rivers. The natural site itself had been modified in order to make it impregnable (unsuccessfully!), with the excavation of a deep moat isolating the pinnacle from the plateau. The site of La Roche-Guyon was also fortified at the end of the

Fig. 3.7 Medieval castles in the Seine valley. A. Château Gaillard, Les Andelys (Photo C. Giusti)

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Fig. 3.8 The human impact on the landscapes: Haute-Isle (E of La Roche-Guyon). (a) The Assumption troglodyte church, seventeenth century (Photo C. Giusti) (b) Haute-Isle: the chalk pinnacles, toward Vétheuil. Postcard, ca 1900, coll. J.P. Peulvast. Note the importance of the cultivated area, even on steep slopes (orchards); compare with Fig. 3.1. Upslope, the Lutetian limestone cornice is excavated by multiple quarries, now abandoned

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The Seine River from Ile-de-France to Normandy: Geomorphological and Cultural Landscapes of a Large Meandering Valley

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Fig. 3.9 The Seine River at Lavacourt, painting by Claude Monet, 1880. Dallas Museum of Art, Munger Fund (Public Domain). Note the partly vegetated sand banks in the middle of the shallow channel

twelfth century, in order to watch both the Seine and Epte valley from the top of a 38 m high keep built on a crest between two steep funnels. Reinforced by two surrounding walls in the thirteenth century, it later lost 22 m of its height. Subterranean stairs connect it to the modern castle built in the sixteenth to eighteenth centuries in the partly artificial cliff shaped below the old keep. Like the castle, the surrounding village comprises many troglodyte dwellings, called “boves.” Natural caves are scarce and rather small in the porous chalk (Rodet 1991), but many cavities perforate the pinnacles. Most of them were hollowed out as premises for breeding pigeons or making wine. They are already mentioned in the seventeenth century by the poet Boileau, the nephew of whom ordered the excavation and construction of a troglodyte church in 1670, at Haute-Isle (Fig. 3.8a). The concave sides of the meanders are also known for their vegetation adapted to the high lime content of their thin rendzina soils. Although rich in protected species of Mediterranean-alpine affinities representing heritages of warmer Holocene times, the grass formations typical of the steepest slopes exposed to the south between the funnels tend to recede owing to the abandonment of the former pastoral activity. Among those that are progressively occupying these slopes and closing the landscapes, many

tree species derive from the fruit trees which formerly were grown here together with vine. Photos and postcards dating to the beginning of the twentieth century show an entirely cultivated landscape, with narrow plots elongated in the slopes, even in their steepest parts (Fig. 3.8b). This may explain the erosion of the already thin soils. Currently, actions of protection (such as the classification of the “coteaux de La Roche-Guyon” as ZNIEFF or zone of faunistic and floristic interest) hardly succeed in maintaining the calcicole grasslands in spite of their botanic value (various species of orchids, in particular). However, grasslands are maintained around Château-Gaillard, owing to the Natura 2000 program which helped restoring sheep breeding (Dumont-Fillon 2002). These spectacular landscapes face convex lobes where vast sand pits and other shallow depressions reflecting former sand and gravel extraction only leave scattered rural or wooded areas, around isolated villages and farms. Some of them were reforested or used as golf links (Moisson), whereas others, excavated below the water table, were transformed in lakes dedicated to nautical leisure (Sandrancourt, Lavacourt, Poses) or bird protection and reproduction (Guernes, Moisson, Bernières, Poses). The river itself was strongly modified: its shallow mobile channels and islands,

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still visible on Monet’s paintings (around 1880) (Fig. 3.9), were replaced by a large fluvial way artificially deepened through dredging and construction of dams and locks (Méricourt, Port-Mort, Amfreville; Fig. 3.2b). Only big winter floods resuscitate for a while the former systems of anastomosing channels in the modern alluvial plain (Fig. 3.1). These heavily transformed landscapes are hardly reminiscent of those represented by Corot, Maugendre, Monet (Skeggs 1988), and the other artists who had visited the region or settled there. However, not only the changing parts of the landscapes were painted but also the fields, crops, curtains of willows, alders and poplars along the Seine River, and natural or artificial water stretches reflecting variable skies. Permanent elements were also immortalized such as Château-Gaillard and the chalk pinnacles at Les Andelys, by Joseph M. W. Turner, Paul Signac, or Félix Vallotton, and the hillsides of Vétheuil, Rolleboise, and Giverny by Claude Monet, Theodore Robinson, or Maximilien Luce. Even the twentieth century comics art valorized some of them, since the site and castle of La Roche-Guyon were used by Edgar P. Jacobs (2007) as the scenery (between the Cretaceous and an apocalyptic future!) of “Le Piège diabolique,” one of the adventures of Blake and Mortimer. Thus, in spite of the extractive activity, still ongoing in parts of the valley floor, the harmony of the landscapes is preserved forever through these famous works which contribute to give this region its unique

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combination of natural and cultural heritages, making it a high place of “cultural geomorphology” (Panizza and Piacente 2003).

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