Nearshore Sand Research Articles

A coupled approach for planning in vulnerable coastal landscapes

One of the most problematic steps in planning and management of vulnerable coastal systems under high level of uncertainties is anticipating potential design scenarios where multiple spatial scales interact. The mutual interference between beach morphodynamics and infrastructural needs of the wide territory poses several questions to urban planners and architects. In this study we assess the ability of the proposed coupled approach of MIKE 21 Spectral Wave and XBeach to significantly improve our understanding of vulnerable barrier beaches in urbanized areas, and hence to contribute to improved system design and management. Specifically, to improve the result accuracy and the time-computational efficiency of the proposed coupled approach, an additional module was developed. Located in the West Metropolitan Area of Cagliari city (Sardinia, IT), the barrier beach of La Playa is an important evacuation route that has experienced a coastal squeeze process under the increase in magnitude and frequency of sea storms. From an extensive beach survey, the “whole model composition” supports the selection of the territorial scale as the reference for defining a potential design scenario at the local scale in La Playa beach. While ordinary (10-year return time) storms create a nearshore sand berm with a protective function for the barrier beach and evacuation route against future storms, extreme (140-year return time) storms significantly erode the beach with a shoreline moving approximately 15 m landward and an overwash of Qcrest >20 l/m/s. Acting as a rigid impermeable obstacle against landward barrier migration, the evacuation route is destroyed. Urban planners and architects should consider the downgrade of the evacuation route as a part of a design potential scenario capable of minimizing the territorial vulnerability and reducing the local vulnerability. Rebuilt with environment-friendly functional road materials, this design scenario can also define a new flexible landward limit of the barrier beach and restore an eventual migration.

Erosion-deposition Prone Assessment Along the Kelantan and Terengganu Coasts Due to Sea Level Rise

The erosion-prone zone is characterised by nearshore sand formed by the combined action of tides, wind, and recurring waves crashing on the beach. By running perpendicular to the coastline and bathymetry, 51 cross-shore sections were chosen from a total of 54 to study longshore transport along the beaches of Kelantan and Terengganu. The hydrodynamic model was used to determine water level, current speed, and spectral density, while the Spectral Wave Model and LitDrift were used to construct boundary wave variables and Net Transport across each sector. The model output was compared to previously published erosion-prone zones in the NCES Report (2015), and the results were agreed. The net transfer varies based on the angle of the coastline, the direction of the waves, and the beach profile. The net transport ranges from -693,000 m3/year to 444,000 m3/year depending on the beach profile, wave direction, and angle of the coastline. Net transit for each section was also calculated for 2030, 2050, and 2100, taking into consideration sea level rise. The most recent IPCC assessment (AR6) was applied to generate SLR forecasts for year 2030, 2050, and 2100. According to the statistics, all sections are expected to increase in year 2030, whereas only 53% and 67% are expected to develop in year 2050 and 2100, respectively. From 2030 to 2050 and 2100 to 2020, total net transport along the Kelantan and Terengganu beaches grows by 9.5%, 10%, and 4.5%, respectively.Net transportation is expected to grow until 2050, then steadily decline until 2100. However, by using a better anticipated wave model, the results of this inquiry can be improved.

Uncertainty in Nearshore Sand Bar Migration

AbstractA coupled nearshore hydrodynamics and sediment transport model with adjoint‐based uncertainty quantification has been applied to sand bar morphodynamics in the Duck94 field experiment (Duck, NC). The model, which is based on previously established physical process formulas, is capable of producing accurate predictions of sand bar migration during the experiment. However, reasonable perturbations to the model inputs—namely initial conditions, boundary conditions, and calibration coefficients—can produce a range of model predictions. This range is taken to represent the potential for uncertainty of the model, for scenarios where one or more model inputs are poorly constrained. Experiments are presented that quantify the relative impact of different input types on uncertainty, and the results are contrasted for accretive versus erosive wave conditions. During accretive conditions (shoreward bar migration), uncertainty is dominated by the growth of errors in initial conditions, owing to positive feedbacks in the model. In contrast, during erosive conditions (seaward bar migration), there is a smaller impact of errors in initial conditions, and uncertainty is instead dominated by errors in sediment transport coefficients. The results thus point to qualitative differences in the nature of nearshore morphodynamic uncertainty under different wave conditions, with a greater role of internal error growth (positive feedbacks) during accretive conditions and errors in model physics being more important during erosive conditions.

Multi-Annual Dynamics of a Coastal Groundwater System with Soil-Aquifer Treatment and Its Impact on the Fate of Trace Organic Compounds

The combination of managed aquifer recharge (MAR) with soil-aquifer treatment (SAT) has clear advantages for the future sustainable quality and quantity management of groundwater, especially when using treated wastewater. We built a Marthe flow and transport model of an MAR–SAT system located in a near-shore sand aquifer, for quantifying the influence of environmental factors (climate, tides, and operational conditions) on the coastal hydrosystem with regard to the fate of trace organic compounds (TrOCs). The simulations show the impact of these factors on flow rates and dilution, and thus, on the potential reactivity of TrOCs. The dilution of secondary treated wastewater (STWW) is variable, depending on the operations (feeding from infiltration ponds) and on shore proximity (dilution by saltwater). We show that, close to the ponds and during infiltration, the attenuation of TrOC concentrations can be explained by reactivity. At the natural outlet of the aquifer, the simulated average residence times ranged from about 70 to 500 days, depending upon seasonal dynamics. It is important to study TrOCs at site scale in order to anticipate the effect of natural variations on the SAT and on the fate of TrOCs.

Sedimentary and diagenetic characteristics of the Z21 field in the Huizhou depression, Pearl River Mouth basin, South China Sea

The Huizhou Depression in the Pearl River Mouth basin has prospective hydrocarbon potential, with Miocene sandstones as its main oil and gas-bearing reservoir. The sandstones in Miocene formation of the Z21 offshore oil–gas field composed of medium-grained, moderately sorted subarkose and lithic arkose. In this study, a total of six depositional lithofacies, namely Massive fine- to medium-grained sandstone (Sm), ripple cross-laminated fine-grained sandstone (Sr), parallel-laminated siltstone and claystone (Fl), lenticular siltstone (Sl), parallel-bedded fine-grained sandstone (Sp), wavy laminated siltstone (Sw), and two depositional systems, namely nearshore sand bar (SB) and sand sheet (SS) were identified based on core observations and seismic study. Distributions of the porosity (13.9%) and permeability (35.8 mD) reveal that the Miocene sandstones have characteristics of low porosity and low permeability, with high heterogeneity. The sedimentary system, primary texture and diagenesis jointly control the reservoir quality. Sandstones with sand bars as well coarse-grained tend to exhibit a higher quality. Mechanical compaction and calcite (average 6.81%) cementation are the major determinants to reductions in porosity and permeability. The total clay minerals (average 5.27%) generally lead to reduction of porosity, whereas chlorite coatings and illite within a certain content range may enhance the preservation of porosity in eodiagenesis. Dissolution of feldspar and debris contribute significantly to improving the reservoir quality.

Complex drivers of reef-fronted beach change

Royal Hawaiian Beach in Waikīkī plays an essential role in Hawai‘i's tourism-based economy. To inform development of management policies, we conduct two years of weekly ground and aerial surveys (April 2018 to February 2020) to track change on this chronically eroding beach. We use multiple linear regressions, Self-Organizing Maps (a form of cluster analysis), remotely sensed nearshore sand fields, hydrodynamic modelling, and monitoring of key physical processes to identify the principal drivers of beach change. Our results show 12 months of subaerial accretion (+2400 ± 59 m3) followed by 10 months of erosion (−3090 ± 51 m3) for a net loss of 690 ± 51 m3, and document that interannual variations in beach width and volume overprint seasonal patterns. Notably, a seasonal signal is recorded in the topographic structure of the beach. We test the relationship of beach volume and width to variations in wind, water level, wave energy flux generated from southern hemisphere swell, and wave energy flux from locally generated trade-wind waves. We identify three beach segments and three nearshore sand fields that form a sand-sharing, source-sink network, yet operate quasi-independently. Our analysis reveals that individual beach segments and their adjacent sand fields experience coherent (simultaneous) gains and losses of sand, suggesting that alongshore sediment exchange is dominant over cross-shore exchange. The main drivers of beach change are variations in water level and wave energy flux. Beach volume and width both vary with nearshore sand cover, indicating that free exchange with nearshore sources is intrinsic to beach variability. Our results suggest that rising sea level and extreme El Niño-Southern Oscillation events will contribute to Royal Hawaiian Beach destabilization, which may amplify erosional events and increase the cost of future beach maintenance.

Współczesne doświadczenia i trendy w stosowaniu sztucznego zasilania polskich brzegów morskich i zalewów ze szczególnym uwzględnieniem Półwyspu Helskiego = Recent experience with and trends in the artificial nourishment of marine and lagoon beaches in Poland, with a particular focus on the Hel Peninsula

Artificial beach nourishment is one of key methods preventing coastal erosion and flooding, acting in support of the maintenance of much-disturbed coastal environments and their much-desired recreational functions. Beach fills have been implemented since the 1930s, though relevant conceptual studies in Poland were elaborated in the 1960s and 1970s. Recommendations at that time included a maximisation of the use made of sand dredged from navigation channels and canals, with a view to this being used to nourish abraded beaches near ports. In 1978, sand by-passing was implemented successfully at the Dźwirzyno and Rowy fishing harbors, with regular dredging of the approach channels and harbour canals being combined with the pumping of a water-sand mixture on the lee (eastern) side of breakwaters. These systems have remained operational through to the present day. Between 1980 and 2014, 32.2 M m3 of sand were deposited along the Polish coast and lagoon shores. This offered partial compensation of the reduced nearshore sand deficit, and served to increase resilience of beaches and the backshore in the face of erosion and inundation, while also helping with the contamination of beaches due to uncontrolled emissions in the course of events of the latter type. More than half of the total fill volume was deposited along the offshore coast of the Hel Peninsula, where a comprehensive scheme for coastal protection was implemented between 1989 and 1995. Following Poland’s adoption of the Coastal Protection Act 2003, fills became the most popular coastal-protection measure. Between 2004 and 2014 this measure was resorted to predominantly along offshore stretches of the Hel Peninsula, and at beaches adjacent to open sea ports on their lee (eastern) sides (including harbours from Łeba along to Dziwnów). Fills were also performed along the shores of the Gulf of Gdańsk, where erosion processes have accelerated in recent decades; and at the open-sea beaches near Jarosławiec, Ustronie Morskie and Niechorze. The latter installations operated in support of existing protection schemes. Comprehensive protection of the soft cliff between Rewal and Trzęsacz was also inaugurated, the background erosion tendencies ongoing their having coincided with anthropogenic activities causing disruption to local geodynamic processes. Since the time of adoption of the Coastal Protection Act, a total fill volume of 10.5 M m3 has been deployed, see Table 1. This represents about one-third of all the filling done from 1980 until 2014. Many positive changes are to be identified along the open-sea coast of the Hel Peninsula, on which more than 17.5M m3 of sand were deposited in the years from 1989 through to 2014, cf. Table 1, Figs. 3, 4 and 5. The large fill volumes achieved during the first 5 years of implementation of the protection scheme along the Peninsula resulted in rehabilitation of the nearshore seabed to such an extent that follow-up re-nourishment only needed to assume a lesser intensity. Morphometric parameters along the nourished beaches allow for them to be classified as very highly resilient in the face of hydrodynamic forces.Since erosion tendencies prevail in Poland’s coastal zones, any cessation of beach fills may result in a gradual loss depletion of the level of safety achieved. Thus, annual deposition of several hundred thousand m3 of sand along the offshore beaches of the Hel Peninsula continues to represent an absolute necessity if the current level of resilience is to be maintained. Reduction of nearshore sand deficits by way of beach filling represents the only method of preventing negative beach responses. Re-nourishments are determined by hydrological and morphodynamic factors, and should gain incorporation into the protection actions being planned by coastal authorities.

Coastal erosion and sediment reworking caused by hurricane Irma – implications for storm impact on low‐lying tropical islands

AbstractHurricane Irma (September 2017) was one of the most devastating hurricanes in recent times. In January 2018, a post‐hurricane field survey was conducted on Anegada (British Virgin Islands) to report on the erosional and depositional evidence caused by Hurricane Irma's storm surge and waves. We document the type and extent of hurricane‐induced geomorphological changes, allowing for an improved risk assessment of hurricane‐related inundation on low‐lying islands and carbonate platforms.Anegada's north shore was most impacted by Hurricane Irma. The surge reached about 3.8 m above sea level and onshore flow depths ranged between 1.2 to 1.6 m. Storm wave action created 1 to 1.5 m high erosional scarps along the beaches, and the coastline locally retreated by 6 to 8 m.Onshore sand sheets reached up to 40 m inland, overlie a sharp erosive contact and have thicknesses of 7 to 35 cm along the north shore. In contrast, lobate overwash fans in the south are 2 to 10 cm thick and reach 10 to 30 m inland.Moreover, the hurricane reworked a pre‐existing coast‐parallel coral rubble ridge on the central north shore. The crest of the coral rubble ridge shifted up to 10 m inland due to the landward transport of cobbles and boulders (maximum size 0.5 m3) that were part of the pre‐hurricane ridge.A re‐survey, 18 months after the event, assessed the degree of the natural coastal recovery. The sand along the northern shoreline of Anegada that was eroded during the hurricane and stored in the shallow water, acted as a nearshore source for beach reconstruction which set in only days after the event. Beach recovery peaked in February 2018, when beaches accreted within hours during a nor'easter‐like storm that transported large volumes of nearshore sand back onto the beach.

Short-term seasonal changes of the Dzita beach of Ghana using geographic information system and photogrammetry

Coastal erosion has become an issue globally. As the sea level continues to rise due to global warming, projections are that erosion would increase. To address the issue sustainably, relevant scientific information such as sediment transport and shoreline dynamics is required at local scales. Over the years, erosion at the eastern coast of Ghana has been mainly evaluated using low-resolution imagery due to the challenges in retrieving high-resolution data in the nearshore region. An unmanned aerial vehicle (UAV) approach was used to assess beach evolution on a seasonal and short-term basis between May 2018 and December 2019. Using the UAV approach, shoreline changes, sediment volume changes, and profile elevation parameters were extracted for the Dzita beach of Ghana. Shoreline changes indicated the dominance of erosion during the first and third phases (May 2018–December 2018 and June 2019–December 2019, respectively) at a rate of −7.23 ± 0.23 and −4.85 ± 0.23 m/yr, whereas the second phase (January 2019–June 2019) showed accretion of +8.44 ± 0.23 m/yr. Beach profiles from the first, second, and third phases had steep and gentle slopes, respectively. From these observations, it was recommended that soft engineering approaches such as beach nourishment should be implemented to protect the shoreline and strict prevention of nearshore sand mining and gravel mining. It is also possible that the beach could go through a cycle of changes. Further studies using this same approach should be done as well as probing into other parameters such as nearshore bathymetry to have a better understanding of beach dynamics as envisaged.

Baseline patterns of structural and functional diversity of benthic amphipods in the western Arabian Gulf

This work presents the structural and functional traits of benthic amphipods in the Saudi waters of the Arabian Gulf. Sixty-two species belonging to 37 genera and 17 families were recorded. Sensitive species such as Grandidierella bonnieroides, G. exilis, Gammaropsis atlantica and Caprellidea indet., were mostly dominant. The average values of richness, density and diversity (H′ log2) were 11 ± 1, 512 ± 232 ind. m-2 and 3.1 ± 0.1 respectively. The density decreased with increased in depth (nearshore (NS) - 784 ± 445 and offshore (OS) - 222 ± 28, p = 0.023), while evenness (NS – 0.93 and OS -0.94) and diversity (NS – 3.10 and OS - 3.18) were unaffected by depth. Interstitial space dwellers (56.76%) and surface deposit feeders (60.16%) were dominant in the nearshore sand substratum. However, domicolous (72.2%) with suspension and surface deposit feeders (71.7%) were more in offshore silt sediments. The combination of depth, pH and TPH (p = 0.249) influenced the distribution of amphipods.

Nearshore Topographical Changes and Coastal Stability in Nam Dinh Province, Vietnam

Recently, the coastal zone in Vietnam has experienced more intensive sea attacks due to severe typhoons, climate change, and humsection an activities. Sea level rise has been recorded all along the coast. Moreover, sand exploitation and engineering measures have significantly changed local reliefs and led to apparent sea water level change on the coast of Nam Dinh province. Coastal erosion and sea dike failures have become a serious problem in the region. The site investigation of nearshore topography shows the recent changes to the coast. Hydrodynamic models show that changes of relief and increased wave attacks on dikes. The main reason for sea dike instability is soil erosion due to wave topping; meanwhile, the dikes are stable in terms of sliding. The coast should be reinforced with properly constructed revetments, wave topping preventive measures, and nearshore sand exploitation should be halted.

Sand transport in the northeastern Caribbean characterized by wind-wave-current data

Sand transport around the northeastern Caribbean Virgin Islands (VI) is studied using global data-assimilation products and satellite measurements; with a focus on seasonal and event characteristics in the period 2002–2019. A review of applied research and a local statistical analysis indicate that currents accompanied by waves and wind mixing are capable of scouring near-shore sand bars.VI area (18.4–18.6N, 65.5–64.5W) time series analysis offer insights on the processes underlying suspended sediment concentrations estimated by 5 km resolution MODIS and VIIRS satellite red-band radiance. The winter season peak in turbidity derives from trade wind-driven waves and currents that reach critical thresholds to mobilize and transport the coarse sands. Instead of wave height, wave steepness and mixed layer depth are applied as coefficients to HYCOM3 near-surface currents, to create a multi-variate sand transport index. Statistical regression shows that a strengthened North Atlantic anticyclone and associated winter trade winds in the VI archipelago results in surface cooling and a deep mixed layer, making steep waves and westward currents more effective in sand transport.The leading case of satellite red-band radiance followed many months after the passage of tropical cyclones in September 2017. A sustained spell of intense trade winds in February 2018 induced 3 m waves of 3% steepness and near-surface currents up to 0.5 m/s. Rapid sea level oscillations >0.05 m suggest that long-period waves joined local wind-waves to mobilize coarse sands within a mixed layer >50 m deep. The plume of sand exhibited composite VIIRS red-band radiance of 0.1 W m−2 μm−1 sr −1; supplying coarse light-colored sands to downstream Caribbean islands.This study has universal application to near-shore sand transport by demonstrating the use of a high-resolution multi-variate index from freely available global data-assimilation products. Given rising sea levels, beach erosion and limited field data, such an index is an essential tool in coastal management.

Assessing the Influence of Changes in Shoreface Morphology since the 19th Century on Nearshore Hydrodynamics and Shoreline Evolution in Northern France: A Modeling Approach

Latapy A.; Hequette A.; Nicolle A., and Pouvreau N., 2020. Assessing the influence of changes in shoreface morphology since the 19th century on nearshore hydrodynamics and shoreline evolution in northern France: A modeling approach In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 542–547. Coconut Creek (Florida), ISSN 0749-0208.The shoreface off the coast of northern France is characterized by the presence of numerous tidal sand banks, forming linear shore-parallel or slightly oblique massive sand bodies. Digitization of historic hydrographic field sheets from the French Hydrographic Service (Shom) archives enabled to produce Digital Elevation Models (DEMs) of the seabed morphology at different dates since the early 19th century. Our analyses of bathymetry changes based on differential DEMs showed significant morphological variations across the shoreface near Calais during the 19th and 20th centuries, which are largely due to changes in nearshore sand bank morphology and position. Sand bank mobility can be partially explained by tidal current asymmetry, inducing an elongation and an alongshore migration of this sand body in the direction of the net residual tidal current. Observed changes in shoreface and nearshore morphology attempt to be related with possible variations in hydrodynamics, this paper presenting the results obtained on tidal currents. TELEMAC-2D model was used to simulate 2D velocity field and water depth during a spring and neap tidal cycle over bathymetry grids based on historical bathymetric soundings. Depending on the bathymetric setting, modeling of tidal residual currents revealed notable increases or decreases in residual current velocity during distinct time periods, particularly in nearshore areas, which may lead to seabed erosion where current strengthening is observed through time or conversely to sediment accumulation in areas of decreasing current velocity. These results are consistent with the shoreline changes that occurred during the 20th century, with a correspondence between nearshore areas of decreasing (or increasing) residual current velocity and adjacent shorelines that were affected by seaward progradation (or erosion), suggesting strong links between changes in seabed morphology over the shoreface and shoreline evolution.

Late-Holocene shoreline responses to competing shelf, bay, and beach accommodation spaces under conditions of relative sea level change, and the potential for future catastrophic beach retreat in the Columbia River Littoral Cell, Washington and Oregon, USA

The Columbia River Littoral Cell (CRLC) (160 km in length) provides opportunities to compare competing accommodation space relations under different conditions of relative sea level change. The CRLC system includes abundant littoral sand supply from the large Columbia River, late-Holocene prograded beach plains and barrier spits (0.5–5 km in width), two large marine-dominated estuaries (Willapa Bay and Grays Harbor), and a high-wave-energy inner-shelf. Littoral sand accumulation rates in prograded beach plains and barrier deposits are based on paleo-shoreline positions that are dated by great-earthquake catastrophic beach retreat scarps (n = 10) from 0.3 to 5.0 ka. The retreat scarp timelines are mapped in across-shore GPR transects (n = 79), yielding timeline-bounded polygons (n = 247). The polygons are evaluated for littoral sand volume and bounding ages, yielding volume accretion rates (m3 ka−1), which are summed for the four CRLC subcells; Clatsop Plains (27.4 × 106 m3 ka−1), Long Beach (19.8 × 106 m3 ka−1), Grayland Plains (15.9 × 106 m3 ka−1), North Beaches (11.7 × 106 m3 ka−1). Major submarine sinks of littoral sand, including the inner-shelf and large marine-dominated estuaries, are evaluated for increased littoral sand accommodation space that could result from potential future sea level rise of 1, 2 and 3 m during the next century or two. The estimated beach and nearshore sand erosion needed to fill the increased submarine accommodation space from a 2.0 m rise in relative sea level would result in averaged beach retreat values of ~0.7 km (Clatsop Plains), ~1.2 km (Long Beach), and ~ 1.3 km (Grayland Plains), about 30–50% larger than previous estimates based on the Brunn method. These catastrophic shoreline retreat distances (0.7–1.3 km) represent 25–50% of the present widths of prograded barrier spits and beach plains. They serve as warnings about future catastrophic beach erosion resulting from potential future SLR in other similar barrier spit and beach plain shorelines worldwide.

Holocene Transgressive Sands on the Nearshore of a Micro-tidal Shelf

Lee, H.J.; Lee, S.H.; Baek, Y.S., and Lim, H.S., 2020. Holocene transgressive sands on the nearshore of a micro-tidal shelf. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 553-557. Coconut Creek (Florida), ISSN 0749-0208.A beach retreat by the Holocene sea-level rise is commonly observed in shelf environments. To investigate into a consequence of the beach retreat in a micro-tidal shelf, surface and cored sediments were sampled from a coastal area around a stream in the eastern coast of Korea and were analyzed texturally. A coastal stratigraphy is constructed with three units representing fluvial sediments, eolian sands and beach sands in an ascending order. This stratigraphy results from the Holocene transgression. The textural characteristics of the units are compared with those of the surficial samples to determine the origin of surficial sands. As a result, the nearshore sands in the study area are most probably the erosional remnants of the antecedent eolian and beach sands. This study exemplifies the Holocene transgression over a narrow, steep shelf whereby active shoreface erosion left portions of beach sediments behind in small estuarine environments.

Cross-shore modelling of multiple nearshore bars at a decadal scale

This paper presents a numerical model designed to simulate subaqueous cross-shore profile behavior, including response of feeder mounds and barred systems. The present model development builds on the semi-empirical model proposed by Larson et al. (2013), designed to simulate the evolution of longshore bars exposed to incident waves, as well as the exchange of material between the bar and the berm region. Here, efforts are made to expand the theory for the evolution of a single-bar to a 2-bar system, where the volumes of the individual bars (inner and outer) and their responses are modeled. In order to investigate the predictive capacity of the model, this exploratory numerical tool is first calibrated and validated against data from Duck, North Carolina, USA, where 2 bars typically appear (inner and outer). Field data derived from nearshore sand placement projects (Silver Strand State Park, California, and Cocoa Beach, Florida, USA), involving the construction of artificial longshore bars, are also employed to test the model in complex situations with diverse wave climates and typical beach profile shapes. The study presented in this paper shows that the equilibrium-based model is skilled at predicting the time-varying volume of the outer bar (ε = 0.39; NMSE = 0.24), suggesting that this morphological feature is strongly influenced by offshore wave forcing in a predictable, equilibrium-forced manner. Model skill was lower (ε = 0.51; NMSE = 0.29) when predicting the inner bar evolution at Duck, remaining questions about the predictability and the equilibrium-driven cross-shore behavior of more transient features. Model prediction of the evolution of feeder mounds (artificial bars) proved to be also successful through description of hypothetical bars characterized by zero equilibrium bar volume, leading to a good agreement with the field observations. Overall, the potential for using rather simple models to quantitatively reproduce the main trends of cross-shore volume changes in bars in a time perspective from years to decades has been demonstrated.

Nearshore Sandbar Classification of Sabaudia (Italy) with LiDAR Data: The FHyL Approach

An application of the FHyL (field spectral libraries, airborne hyperspectral images and topographic LiDAR) method is presented. It is aimed to map and classify bedforms in submerged beach systems and has been applied to Sabaudia coast (Tirrenyan Sea, Central Italy). The FHyl method allows the integration of geomorphological observations into detailed maps by the multisensory data fusion process from hyperspectral, LiDAR, and in-situ radiometric data. The analysis of the sandy beach classification provides an identification of the variable bedforms by using LiDAR bathymetric Digital Surface Model (DSM) and Bathymetric Position Index (BPI) along the coastal stretch. The nearshore sand bars classification and analysis of the bed form parameters (e.g., depth, slope and convexity/concavity properties) provide excellent results in very shallow waters zones. Thanks to well-established LiDAR and spectroscopic techniques developed under the FHyL approach, remote sensing has the potential to deliver significant quantitative products in coastal areas. The developed method has become the standard for the systematic definition of the operational coastal airborne dataset that must be provided by coastal operational services as input to national downstream services. The methodology is also driving the harmonization procedure of coastal morphological dataset definition at the national scale and results have been used by the authorities to adopt a novel beach management technique.

Sedimentary model of K-Successions Sandstones in H21 Area of Huizhou Depression, Pearl River Mouth Basin, South China Sea

AbstractThe nearshore sand bar-sheet sedimentary system of the K-Successions sandstones of the Zhujiang Formation (23.8-16.5 Ma) in H21 Area of Huizhou Depression, Pearl River Mouth Basin has been identified in this research according to lithological characteristics, lithofacies, sedimentary sequence and seismic attributes. Seven lithofacies were recognized: fine-grained massive sandstone (Sm), fine-grained trough cross-bedded sandstone (St), fine-grained planar-bedded sandstone (Sp), fine-grained ripple cross-bedded sandstone (Sr), fine grained horizontally-bedded sandstone (Sh), laminated claystone with interbedded siltstone (Fl) and massive mudstone (Fm). Three sedimentary microfacies were further divided: sand bar, sand sheet and interbar. With the progradation and retrogradation process influenced by sea level changing, delta evolution of K-Successions sandstones in H21 area of Huizhou Depression can be divided into four stages: the early stage of the transgressive systems tract, A/S>1; the medium stage of the transgressive systems tract, A/S>1; the end stage of transgressive systems tract; the stage of the highstand systems tract, A/S<1. Different evolution stages controlled the sandstones distribution.

Spatial configuration of sand and mud in the lacustrine nearshore sand bar deposits and its geological implications

Different configurational orders of sand bodies and interlayers in lacustrine nearshore sand bar reservoirs frequently interact, causing complicated genesis and distribution of argillaceous sediments, as well as other issues. This paper investigates the spatial configuration of sand and mud in the sand bar reservoir, and analyzes its internal structure. Modern sand bar deposits in the Xiashan Lake, Shandong Province, China, were analyzed and compared with the sand bar reservoirs of the Member 2 of the Paleogene Shahejie Formation in the Banqiao Sag, China. The configurational mode of sand bar deposits was explored from the perspective of the spatial distribution and composition relationships between sand and mud. Based on the alternate deposition characteristics of sand and mud in the longitudinal direction, lacustrine nearshore sand bars can be divided into three sedimentary combination patterns: thin-sand and thin-mud interbed pattern, thick-mud thick-sand pattern, and thin-mud thick-sand pattern. Their mud components manifest as the deposition of fine-grained lithofacies of multiple genetic types. These include (semi-)deep lacustrine mud, sand and mud interbedded beach, argillaceous sediments in the water retention area behind the bar, and fall-silt seams that resulted from flood discharge. By summarizing the specific developmental locations and sequential relationships of each fine-grained argillaceous facies in modern sand bar deposits, a depositional process-based argillaceous sediment composition model is proposed. Based on this, this paper discusses the spatial configuration of sand bodies and argillaceous sediments in sand bar reservoirs, and introduces the typical stratigraphic structures of sand bars in two environments, i.e., vertical superposition and lateral migration. In lacustrine nearshore sand bar reservoirs, the deposition and preservation degrees of mud mainly depend on three factors: accommodation space change, frequency of base-level cycles, and exposure-erosion time. These in turn influence the continuity and relative contents of sand and mud in reservoirs. The distribution of argillaceous sediments forms different orders of interlayers, which affects the heterogeneity and fluid percolation of sand bar reservoirs. Clarifying the space-matching relationship of sand and mud in sand bar deposits provides geological models and information parameters for the refined characterization and modeling of the internal configuration of sand bar reservoirs. Furthermore, this work offers guidance for the optimal adjustment of reservoir development strategies or the optimization of reservoir development plans.

Mesoscale Morphological Changes of Nearshore Sand Banks since the Early 19th Century, and Their Influence on Coastal Dynamics, Northern France

Tidal sand banks are common along the coast of northern France facing the North Sea, where they form linear shore-parallel or slightly oblique sand bodies from shallow coastal areas to depths of tens of meters. Hydrographic surveys have been carried out since the 1830s for mapping the seabed of the coastal zone. An analysis of the bathymetry evolution shows significant morphological changes have occurred across the shoreface since the early 19th century, largely due to cross-shore and longshore sand bank migration. Our results show that nearshore sand banks mainly migrated onshore and gained sediment, especially during the 20th century; acting as temporary sediment sinks, which can in turn serve as sand sources for providing sediment to the coast. Alongshore, the migration and elongation of sand banks can be related to tidal asymmetry that is mostly directed to the east-north-east in the region. Shore-perpendicular movement can likely be explained by the action of shore-normal storm-waves in the nearshore zone after their refraction over shallow offshore sand banks. A seaward displacement of sand banks was also observed. This may be related to the combined action of waves and tidal currents which can induce erosion on one side of the bank, decreasing its width, and eventually leading to its seaward migration. Our observations point out that some nearshore sand banks respond to the action of currents and waves, and interact between each other via feedback morphodynamic processes induced by sand bank morphological changes. The substantial morphologic changes that affected the nearshore zone of northern France during the last centuries probably had large impacts on coastal hydrodynamics and associated shoreline evolution.