Mireille Provansal

Geomorphological evidence for fluvial change during the Roman period in the lower Rhone valley (southern France)

Abstract The hydrological and geomorphological dynamics of the lower Rhone river (southern France) are studied during the Roman period (2nd–1st centuries BC, 2nd–3rd centuries AD). The crossing of archaeological and radiocarbon dating methods allow to study events at a pluridecadal to centennial scale. From the Avignon town to the delta, the 15 sites where Roman fluvial dynamics were recorded show higher flooding frequencies, higher energy levels during floods, rises in the marshes or groundwater levels, and/or active morphological dynamics such as channel migrations from 1st century BC to 1st–2nd centuries AD, with respect to the encircling periods. Although this fluvial change does not reach the amplitude of great climatic events such as the Little Ice Age in the Rhone valley, we show that it is also perceived in other parts of the catchment and could have a climatic origin. However, this event is not recorded in the immediate Mediterranean environment of the lower Rhone, so that the Rhone appears to efficiently transmit a foreign climatic change.

Recent morphological channel changes in a deltaic environment. The case of the Rhone River, France

Abstract Channel morphological changes were measured at two sites within the Rhone delta along the main channel of the Rhone River over one century. Results show an average erosion rate of 2.8 mm year−1 during the 20th century and decreasing to

High frequency variations of water flux and sediment discharge during the Little Ice Age (1586–1725 AD) in the Rhône Delta (Mediterranean France). Relationship to the catchment basin

During the 17th and 18th centuries, the Rhone delta recorded high frequency fluctuations in water and sediment influx. These variations resulted from the drastic climatic changes that took place during the Little Ice Age, which were intensified by dense land settlement in the catchment basin. The use of complementary types of information (iconographic and textual archives, photo-interpretation of traces of fluvial metamorphosis, grain size distribution and mineralogy of alluvial infillings) allows a precise study of the major change that affected the Rhone delta in the second part of the 17th and the beginning of the 18th centuries. This change corresponds to a rapid response by the fluvial system and the occurrence of floods that were higher and more frequent on the lower Rhone. It resulted in a rapid change in fluvial environments, i.e. channel infilling, raising of river banks, appearance of crevasses and secondary channels, and accelerated delta progradation. It is associated with the influx of an abundant and exceptionally coarse-grained bottom load. The provenance of these sediments is discussed, using the heavy mineral assemblages they contain, with reference to reworking of previous alluvial deposits, probably due to changes in the active band and episodic loads in the whole catchment basin. The short response time to hydrologic impulse and the importance of the metamorphosis are related to the sediment influx from the Massif Central, whose steeply inclined rivers are close to the delta. The contribution of the northern Alps and the durancian basin (southern Alps) is not as important because of their distance from the delta and the time lag affecting the bottom load transfer downstream. The aims of this study are to investigate the response time, transfer velocity of sandy deposits, and the contribution of different catchment sub-basins to the supply of the Rhone delta. The role of climatic and anthropic factors are also discussed.

Evidence for an early land use in the Rhône delta (Mediterranean France) as recorded by late Holocene fluvial paleoenvironments (1640-100 BC)

Abstract The overall objective of this paper is to describe the late Holocene (1640–100 BC) sedimentary and biological evolution of the Rhône–delta–plain, to interpret the sedimentary facies and palynofacies as the result of the effects of fluvial dynamic fluctuations and relative sea level change and to evaluate the paleohydrological constraints in the development of the land use and settlements of the Camargue. Focus is made on the upper part of VIII core drilled on NE of the Vaccares lagoon. By combining sedimentology, palynology, magnetic susceptibility and archeological data, this study allowed to identify the superposition of three types of paleo-environments (marsh, fluvial floodplain, levee/crevasse splay). This sequence indicates a gradual extension of fluvial environments between the end of the second millennium BC and the 1st century BC. The variability of fluvial dynamic is evident during this period with important flood events which contrast with periods of low flow. Pollen record can be a good marker of the fluvial dynamic variability. The expression of the riparian tree pollen grains in the coarser floodplain deposits could correspond to increased fluvial influence and probably to erosion of riverbank during flood events. The local plants are associated to the low energy sedimentary environments. Focuses are made on the relations between the evolution of the environment and land use. The development of the cereal culture in the floodplain of the Rhone delta has been demonstrated between 1640–1410 and 100 BC. The last alluviation of the Rhone perturbs the research of the archaeological sites in the central part of the delta but the existence of the rural villages from the first part of the first millennium BC is highly possible.

Morphosedimentary behaviour of the deltaic fringe in comparison to the relative sea-level rise on the Rhone delta

Abstract For the first time, mareographic data obtained by the ‘Compagnie du Salin du Midi’ have been used to estimate the relative sea-level rise (RSLR) in the Rhone delta. The results were compared with the data obtained in the Marseille region which is known to be a tectonically stable zone, at least, on the secular time scale. The magnitude of relative sea-level rise is equal to 2.1 mm/year, from which 1 mm/year could be attributed to subsidence. The morphosedimentary behaviour of the deltaic fringe has been analyzed in order to see if the amount of sediment input is sufficient to allow the wetlands to continue to exist with RSLR. The horizontal variations (erosion and progradation) have been quantified from land surface changes obtained by shoreline variation analysis. The vertical accretion is measured using isotopic dating ( 137 Cs). It appears that the eastern part of the mouth of the Rhone is characterized by high sediment input, sufficient enough to offset the recent rise of sea level. The western part remains vulnerable due to the lack of sediment in this area.

Evidence for an early land use in the Rhône delta (Mediterranean France) as recorded by late Holocene fluvial paleoenvironments (1640–100 BC)Preuves d’une mise en culture précoce de la plaine deltaïque du Rhône (France méditerranéenne) enregistrées par les séquences fluviales de l’Holocène récent (1640–100 av. J.-C.).

Abstract The overall objective of this paper is to describe the late Holocene (1640–100 BC) sedimentary and biological evolution of the Rhone–delta–plain, to interpret the sedimentary facies and palynofacies as the result of the effects of fluvial dynamic fluctuations and relative sea level change and to evaluate the paleohydrological constraints in the development of the land use and settlements of the Camargue. Focus is made on the upper part of VIII core drilled on NE of the Vaccares lagoon. By combining sedimentology, palynology, magnetic susceptibility and archeological data, this study allowed to identify the superposition of three types of paleo-environments (marsh, fluvial floodplain, levee/crevasse splay). This sequence indicates a gradual extension of fluvial environments between the end of the second millennium BC and the 1st century BC. The variability of fluvial dynamic is evident during this period with important flood events which contrast with periods of low flow. Pollen record can be a good marker of the fluvial dynamic variability. The expression of the riparian tree pollen grains in the coarser floodplain deposits could correspond to increased fluvial influence and probably to erosion of riverbank during flood events. The local plants are associated to the low energy sedimentary environments. Focuses are made on the relations between the evolution of the environment and land use. The development of the cereal culture in the floodplain of the Rhone delta has been demonstrated between 1640–1410 and 100 BC. The last alluviation of the Rhone perturbs the research of the archaeological sites in the central part of the delta but the existence of the rural villages from the first part of the first millennium BC is highly possible.

Geomorphic Changes in the Rhône Delta During the LIA: Input from the Analysis of Ancient Maps

The morphogenesis of the mouths and shores of the Rhone river delta has been strongly influenced by changes in hydrology associated with climatic deterioration during the Little Ice Age (LIA). The present shape of the delta is related to two avulsions. The progradation of delta-mouth lobes, their morphology (digitated or lobate), and their reworking by marine processes are described here from ancient maps, the interpretation of which has been comforted jointly by the critical viewpoint of the historian and input from previous geomorphic studies. The impacts of climatic oscillations proper to the LIA are analysed and confronted with other factors implied in deltaic morphogenesis such as sediment transfers, accommodation space, marine processes and human interventions, notably from an engineering perspective. The successive metamorphoses of the Rhone delta are, thus, seen to be related to the conjunction of some or all of these factors, depending on the time frame under consideration.

The Lower Valley and the Delta of the Rhône River: Water Landscapes of Nature and History

Linking the Mediterranean to northern Europe, the lower Rhone valley is the major axis of communication in the south of France since the antiquity. The valley ends by a large deltaic plain rich in history and landscapes of international renown. It annually attracts thousands of tourists and nature lovers and artists through several festivals and exhibitions. Original water landscapes were built in the valley and at the contact between the river and the sea (delta). Their development over the centuries is the product of a complex evolution between the natural environment and human history. Numerous archaeological excavations reflect man–environment interactions, emphasising the strong constraint of fluviatile–deltaic environments, and how human societies, since the Greeks and the Romans, found some parades to mitigate the fluvial risk. The geomorphology of the landscapes is most of the time discrete, and we must learn to decipher the old and recent landforms derived from fluvial, lagoonal or marine environments. The landforms are now subject to different aggressions (erosion, pollution) and metamorphoses related to human activities combining with the natural dynamics: the protection of the “nature” has become a real challenge.