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Abstract: On 10th March 2008, the high energy storm Johanna hit the French Atlantic coast, generating severe dune erosion on Vougot Beach (Brittany, France). In this paper, the recovery of the dune of Vougot Beach is analysed through a survey of morphological changes and hydrodynamic conditions. Data collection focused on the period immediately following storm Johanna until July 2010, i.e. over two and a half years. Results showed that the dune retreated by a maximum of almost 6m where storm surge and wave attack were the most energetic. Dune retreat led to the creation of accommodation space for the storage of sediment by widening and elevating space between the pre- and post-storm dune toe, and reducing impacts of the storm surge. Dune recovery started in the month following the storm event and is still ongoing. It is characterised by the construction of “secondary” embryo dunes, which recovered at an average rate of 4–4.5cm per month, although average monthly volume changes varied from −1 to 2m3.m−1. These embryo dunes accreted due to a large aeolian sand supply from the upper tidal beach to the existing foredune. These dune-construction processes were facilitated by growth of vegetation on low-profile embryo dunes promoting backshore accretion. After more than two years of survey, the sediment budget of the beach/dune system showed that more than 10,000m3 has been lost by the upper tidal beach. We suggest that seaward return currents generated during the storm of 10th March 2008 are responsible for offshore sediment transport. Reconstitution of the equilibrium beach profile following the storm event may therefore have generated cross-shore sediment redistribution inducing net erosion in the tidal zone. [Copyright &y& Elsevier]

Abstract: The 9.5km2 Illgraben catchment, located in the Rhône valley in the Central Alps of Switzerland, is one of the most active debris flow torrents in the Alps. In this paper we present sediment yield data collected in 2006 for segments where hillslopes and channels form a fully connected network and contrast these with sediment yields measured for disconnected hillslopes. The data reveal that sediment yields are 1–2 orders of magnitude larger in segments where hillslopes are connected with the channel network than on disconnected hillslopes. Support for this conclusion is provided by observations made on 1959, 1999 and 2004 aerial photographs that the vegetation cover in the disconnected segments is still intact, whereas denudation rates of several centimeters per year in the connected segments have inhibited the establishment of a stable vegetation cover. Furthermore, sediment supplied from hillslopes during the past 40 years has temporarily accumulated along the Illgraben channel, indicating that the channel aggraded over this period and has not yet recovered. An implication of this observation is that initiation of debris flows in the Illgraben catchment is limited more by the availability of intense rainfall than sediment. In contrast, on disconnected hillslopes, sediment flux does not appear to be driven by precipitation. The petrographic composition of the Illgraben fan deposits indicates two distinct sediment sources, one related to rockfall and the other to landslides and debris flows. The presence of clasts from both sources implies multiple processes of erosion, deposition, mixing and re-entrainment in the catchment before the material is exported to the Illgraben fan and to the Rhône River. In addition, delivery of large amounts of coarse-grained sediment to the Rhône causes a modification of the flow pattern from meandering or anastomosing upstream to braided downstream. Hence, the direct connectivity between hillslope and channelized processes in the Illgraben catchment causes not only rapid topographic modifications in the catchment, but also morphologic adjustment in the Rhône valley downstream. [Copyright &y& Elsevier]

Abstract: Since 1834 the Seine estuary (France) has been the site of numerous construction projects with the aim to accommodate and secure boat traffic. Since 1978, the increasing of the activities of Le Havre port, located at the mouth of the estuary, has accelerated the construction work rate. Several dykes, a bridge, and new port facilities have been constructed in rapid succession, modifying considerably the hydrodynamic conditions which sustain a partially vegetated sandy–muddy tidal flat located in the North bank of the estuary between the new port of Le Havre and the Normandy bridge achieved in 1995. The present study deals with the morphological evolution of this zone from 1978 to 2005. The use of a low altitude remote sensing technique combined with traditional methods of ground survey and probes allow to demonstrate the impact of human activities on sedimentary and vegetation dynamics. The Northern mudflat of the estuary is the most affected by these human activities, which surface have reduced of 62% during the last 27 years with an intensified local erosion during the last 27 months corresponding to a loss 1250000 m3 of fine-grained sediment. At the same time, the general sanding up in the channel of the zone has caused a loss of more than 31% of the tidal prism, more than three quarters of which occurred during the last three years. Results also establish that the response times of the sedimentary or topographic readjustment to an installation depend on the extent and the nature of the construction. In fact, the sedimentary readjustments to an installation can be delayed by up to 10 years in the case of the Seine estuary. This delay is explained by a rapid succession of construction works which may occult the effect of a single installation. Except in the case of a dyke built perpendicular to ebb and flood currents, the impacts of these installations reach a hydro-sedimentary equilibrium on the level between 1 and 7 years after their completion. [Copyright &y& Elsevier]

The greatest change in particle roundness, sphericity, and size in most fluvial systems generally occurs in the initial first few kilometers of sediment transport. Observations in natural settings and laboratory experiments have shown that changes, such as increased grain rounding and decreased size due to particle breakage, wear, and attrition, tend to be progressive along the dispersal path. In marked contrast, this study records highly variable and poorly developed particle-texture trends downslope along short (<5 km) channels that extend directly from a high-relief carbonate source area down to the shore of Lake Annecy in the western Alps, SE France. The observed inconsistent patterns are measured in both a region-wide analysis using all collected samples and also in a more specific survey of samples in six different channels incised on the steep, topographically irregular mountain flanks that border the lake. The major factor responsible for the irregular downslope patterns of roundness, sphericity, and size in the Annecy study area is the lateral introduction of sediment into the fluvial channels along dispersal paths. Episodic failure of mechanically unstable sediments and their transport down steep valley walls bring less-abraded sediment of variable shape and size along the dispersal paths. The valley wall sediment influx factor warrants further examination to better interpret sedimentation processes in dissected, high-gradient terrains that border coastal areas. [ABSTRACT FROM AUTHOR]