Проблеми структурної модернізації регіонального ринку трудових ресурсів АПК в експертній оцінці працівників органів регіонального управління

Barriers and sandbars are ubiquitous natural coastal features, whose variability often determines nearshore morphological evolution. Wave-dominated beach profile evolution results from the interaction between wave non-linearities, wave-breaking induced turbulence, undertow, infragravity motions and swash processes. To explore each of these contributions to the sediment transport, the full-scale Barrier Dynamics Experiment (BARDEX II), performed in the Delta Flume in June 2012, provides a new dataset for the rigorous testing of the performance of beach profile evolution models in the case of steep beaches. This new experiment will improve our knowledge on (1) swash zone processes, including infiltration and exfiltration of water into the sand and subsequent groundwater table response, (2) bore-generated turbulence inducing suspend sediment transport, (3) surfzone sandbar dynamics and (4) overtopping/overwash impact on barrier dynamics. This study aims at testing the ability of the process-based beach profile model 1DBeach in the case of a steep beachface and a predominance of plunging breakers. In this context, we tested the model with a morphological sequence characterised by onshore and subsequent rapid offshore sandbar migration for time-invariant wave forcing and falling tide. A simulated annealing algorithm is used to calibrate the model. In this paper, we discuss the model configuration and associated results, as well as the need of intensive high-frequency full-scale data to further develop and improve process-based models

Modelling the alongshore variability of optimum rip current escape strategies on a multiple rip-channelled beach

Rip currents are a leading cause of drowning on beaches worldwide. How bathers caught in a rip current should attempt to escape has been a subject of recent debate. A numerical model of human bathers escaping from a rip current flow field is applied to a 2-km long section of the open beach of Biscarrosse, SW France. The study area comprises 4 rip channels that visually appear similar from the beach, but exhibit different morphologies. Simulations are run for 2 representative hazardous summer wave conditions. Results show that small changes in the bar/rip morphology have a large impact on the rip flow field, and in turn on the alongshore variability of the optimal rip current escape strategy. The overall flow regime (dominant surf-zone exits versus dominant recirculation), which is found to be influenced by the alongshore dimensions of the sand bars adjacent to the rip channel, is more important to rip current escape strategy than rip velocity. Flow regime was found to dictate the success of the stay afloat strategy, with greater success for recirculating flow. By comparison, the dominant longshore feeder current and rip-neck orientation determined the best direction to swim parallel toward. For obliquely incident waves, swim parallel downdrift then swim onshore with breaking waves was highly successful and can become a simple safety message for beach safety practitioners to communicate to the general public. However, in SW France where rip spacing is large (∼400 m), surf-zone eddies have large spatial scales of the order of 100+ m, requiring a large distance (100+ m) to swim to reach safety, therefore requiring good swimming ability. This also shows that in addition to rip current intensity, rip flow regime and the depth of adjacent sand bars, rip spacing is important for defining rip current hazard and the best safety message. Our results also indicate that for normal to near-normal wave incidence, rip current hazard and best rip current escape strategy are highly variable alongshore due to subtle differences in bar/rip morphology from one rip system to another. These findings challenge the objective of developing a universal rip current escape strategy message on open rip-channelled beaches exposed to normal to near-normal wave incidence, even for seemingly similar rip channels

La construcción del espacio rural en el siglo XIX : la introducción del alambrado en la pampa bonaerense

Fil: Caggiano, María Amanda. Instituto Municipal de Investigaciones Antropológicas de Chivilcoy. Universidad Nacional de La Plata; ArgentinaFil: García, María Soledad. Laboratorio de Análisis Cerámico (LAC). Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Paleo, María Clara. Laboratorio de Análisis Cerámico (LAC). Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Adam, Sandra Gabriela. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Dubarbier, Virginia. Laboratorio de Análisis Cerámico (LAC). Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Di Uono, María. Facultad de Bellas Artes. Universidad Nacional de La Plata; ArgentinaFil: Mondino, Diana B.. Facultad de Bellas Artes. Universidad Nacional de La Plata; ArgentinaFil: Scola, Guillermo. Facultad de Bellas Artes. Universidad Nacional de La Plata; Argentin

Modélisation de l’évolution des profils de plage sableuse sur plusieurs mois et apports de l’assimilation de données

Dans ce papier nous présentons un nouveau modèle de profil de plage sableuse réalisant le couplage vagues/transport sédimentaire/évolution bathymétrique avec une approche à phase moyennée. Nous utilisons une paramétrisation récente des effets non-linéaires des vitesses orbitales des vagues au fond permettant d’améliorer les flux sédimentaires vers la côte. Nous validons le modèle numérique pour un cas de migration de barres sableuses vers le bord (Duck, Caroline du Nord) et vers le large (Egmond, Pays-Bas) sur une période de plusieurs jours. Nous montrons que le modèle reproduit avec fidélité l’évolution des profils mesurés en termes de migration et de morphologie, confirmée par des indices de performance (Brier skill) supérieures à 0.5 en fin de chaque simulation. Certaines limitations comme les erreurs en domaine intertidal sont discutées ainsi qu’un cas synthétique d’apport de l’assimilation de données. This paper presents the development of a simple coupled, wave-averaged, cross-shore waves-currents-bathymetry evolution model. A recent parameterization of the freestream nonlinear wave orbital motion is used to improve onshore sediment transport. We compare the model with data gathered at two natural beaches where sandbars move onshore (Duck) and offshore (Egmond) on the timescales of weeks. Reliable simulations of observed sandbar behavior (migration and shape) are obtained, despite mismatch at the upper part of the beach. Synthetic assimilation test cases are performed to overcome missing swash-processes, and are further discussed

Mechanisms controlling the complete accretionary beach state sequence

Accretionary downstate beach sequence is a key element of observed nearshore morphological variability along sandy coasts. We present and analyze the first numerical simulation of such a sequence using a process-based morphodynamic model that solves the coupling between waves, depth-integrated currents, and sediment transport. The simulation evolves from an alongshore uniform barred beach (storm profile) to an almost featureless shore-welded terrace (summer profile) through the highly alongshore variable detached crescentic bar and transverse bar/rip system states. A global analysis of the full sequence allows determining the varying contributions of the different hydro-sedimentary processes. Sediment transport driven by orbital velocity skewness is critical to the overall onshore sandbar migration, while gravitational downslope sediment transport acts as a damping term inhibiting further channel growth enforced by rip flow circulation. Accurate morphological diffusivity and inclusion of orbital velocity skewness opens new perspectives in terms of morphodynamic modeling of real beaches

Alongshore Variability in Crescentic Sandbar Patterns at a Strongly Curved Coast

Sandbars, submerged ridges of sand parallel to the shoreline, tend to develop crescentic patterns while migrating onshore. At straight coasts, these patterns form preferably under near‐normal waves through the generation of circulation cells in the flow field, whereas they decay under energetic oblique waves with associated intense alongshore currents. Recently, observations at a man‐made convex curved coast showed an alongshore variability in patterning that seems related to a spatiotemporal variability of the local wave angle (Sand Engine). Here, we aim to systematically explore how coastline curvature contributes to alongshore variability in crescentic pattern formation, by introducing local differences in wave angle and the resulting flow field. A nonlinear morphodynamic model was used to simulate the patterns in an initially alongshore uniform sandbar that migrates onshore along the imposed curved coast. The model was forced by a time‐invariant and time‐varying offshore wave angle. Simulations show that the presence of patterns and their growth rate relate to the local breaker angle, depending on the schematization of the offshore angle and the local coastline orientation. Growth rates decrease with increasing obliquity as both refraction‐induced reductions of the wave height as well as alongshore currents increase. Furthermore, simulations of variations in coastline curvature show that patterns may develop faster at strongly curved coasts if this curvature leads to an increase in near‐normal angles. This implies that beaches where the coastline orientation changes substantially, for example, due to km‐scale nourishments, become potentially more dangerous to swimmers due to strong currents that develop with pronounced bar patterns

CROSS-SHORE SANDBARS RESPONSE TO AN ARTIFICIAL REEF: AN INTERSITE COMPARISON

International audienceWhile a clear improvement concerning aesthetic considerations using soft submerged breakwater is undeniable, their design has often focused on wave energy decrease in their lee, overlooking their impact on the dynamics of the nearby nearshore sandbar(s). At the beach of Sète (southeast France), the submerged structure clearly affects the natural net offshore migration cycle (NOM) of the former double barred beach. On the contrary, at Narrowneck (Queensland, Australia), the deployment of a multi-functional submerged structure does not affect the cross-shore sandbar processes. These contrasting behaviors are addressed using high frequency video monitoring. After discussing observations at both field sites, a process-based morphodynamic model provides insight into the morphological sandbars response to artificial reefs

Numerical modelling of equilibrium and evolving lightweight sediment laboratory beach profiles

International audienceThe recent advances of numerical beach profile models allowed the simulation of on/offshore sandbar migrations on timescales of weeks to months with fair success. These models were systematically applied to natural, persistently evolving, beaches. In this contribution, we apply our model to small-scale laboratory experiments for which coarse and lightweight sediment is used to satisfy the laws of similitude in the flume. Such experiments can result in equilibrium beach profiles and provide detailed information on the respective role of undertow and wave nonlinearities on sediment transport and the resulting cross-shore sandbar migration. Here we first apply the coupled, wave-averaged, cross-shore waves-currents-bathymetric evolution model 1DBeach to an equilibrium beach profile. The model simulates an equilibrium beach profile with reasonable success. Yet, when applying the best fit parameters to a subsequent rapid onshore sandbar migration, the model fails in reproducing the overall beach profile evolution. Further model calibration on the evolving beach profile sequence shows that the model can actually reproduce the rapid onshore sandbar migration with a significant contribution of acceleration skewness. This suggests that a number of misspecifications of the physics remain in coupled, wave-averaged, cross-shore waves-currents-bathymetric evolution model. In addition, given that best-fit model free parameters are of the same order of magnitude of those found on natural beaches, our study suggests that small-scale experiments with coarse and lightweight sediment can be used to further explore the respective contribution of wave nonlinearities and undertow to sediment transport and the overall beach profile evolution

Sandbar and beach-face evolution on a prototype coarse sandy barrier

On steep beaches, the cross-shore movement of sand in response to ‘erosive’ storm waves and ‘accretive’ swell waves can lead to temporal changes between a barred winter profile and a non-barred summer profile with a pronounced berm in the upper swash zone. Despite recent improvements in predicting berm formation and evolution within process-based morphodynamic models, substantial demand for improvement in understanding swash processes and associated surf–swash sand exchange remains. Here, we analyze bed level data collected on a near-prototype, 4.5-m high and 75-m wide sandy beach (median grain diameter D50 = 430 μm) with a lagoon situated at its landward side. In particular, we distinguish between surf–swash sand exchange (time scale of tens of minutes to hours), the net effect of single and multiple swash events on the entire beach face (time scale of a few seconds to hours), and instantaneous bed variability at 3 cross-shore locations within individual swashes. During ‘erosive’ waves (Hs = 0.8 m, Tp = 8 s) sand on the initially 1:15 planar profile was predominantly eroded from the inner surf zone to be deposited in the outer surf zone as a sandbar, indicating minimal surf–swash sand exchange. Subsequent ‘accretive’ waves (Hs = 0.6 m, Tp = 12 s) caused substantially larger surf–swash sand exchange: the pre-existing sandbar migrated onshore and decayed, with the sand ending up on the beach face in a prominent (up to 0.7 m high), steep (1:6) berm. We found the dynamics of the berm to be governed primarily by wave conditions and the antecedent morphology, with ground water gradients of additional importance when morphodynamic feedback between swash flow and the berm is small. The observed bed level change within a swash and averaged over a swash event could be substantial (several centimeters) during all wave conditions, but the net (i.e., averaged over multiple swash events) bed level change was strongly suppressed because erosive and accretionary swashes nearly balanced. In addition, the local beach face slope could be instantaneously ≈ 25 % steeper or shallower than the median slope, or the initial or final slope. We anticipate that our data will stimulate new model development, as to increase the range of conditions and settings in which morphodynamic models can be applied realistically and reliably

Sandbar and beach-face evolution on a prototype coarse sandy barrier

On steep beaches, the cross-shore movement of sand in response to ‘erosive’ storm waves and ‘accretive’ swell waves can lead to temporal changes between a barred winter profile and a non-barred summer profile with a pronounced berm in the upper swash zone. Despite recent improvements in predicting berm formation and evolution within process-based morphodynamic models, substantial demand for improvement in understanding swash processes and associated surf–swash sand exchange remains. Here, we analyze bed level data collected on a near-prototype, 4.5-m high and 75-m wide sandy beach (median grain diameter D50 = 430 μm) with a lagoon situated at its landward side. In particular, we distinguish between surf–swash sand exchange (time scale of tens of minutes to hours), the net effect of single and multiple swash events on the entire beach face (time scale of a few seconds to hours), and instantaneous bed variability at 3 cross-shore locations within individual swashes. During ‘erosive’ waves (Hs = 0.8 m, Tp = 8 s) sand on the initially 1:15 planar profile was predominantly eroded from the inner surf zone to be deposited in the outer surf zone as a sandbar, indicating minimal surf–swash sand exchange. Subsequent ‘accretive’ waves (Hs = 0.6 m, Tp = 12 s) caused substantially larger surf–swash sand exchange: the pre-existing sandbar migrated onshore and decayed, with the sand ending up on the beach face in a prominent (up to 0.7 m high), steep (1:6) berm. We found the dynamics of the berm to be governed primarily by wave conditions and the antecedent morphology, with ground water gradients of additional importance when morphodynamic feedback between swash flow and the berm is small. The observed bed level change within a swash and averaged over a swash event could be substantial (several centimeters) during all wave conditions, but the net (i.e., averaged over multiple swash events) bed level change was strongly suppressed because erosive and accretionary swashes nearly balanced. In addition, the local beach face slope could be instantaneously ≈ 25 % steeper or shallower than the median slope, or the initial or final slope. We anticipate that our data will stimulate new model development, as to increase the range of conditions and settings in which morphodynamic models can be applied realistically and reliably