Sediment Transfer Research Articles

Sediment leakage on the beach and upper shoreface due to extreme storms

The quantification of sediment exchanges between the beach and the lower shoreface, although being still poorly understood, is required to adequately forecast long-term coastal evolution. The effect of extreme storms on the morphodynamics of the nearshore and the sediment budget of the coastal zone seems to be strongly conditioned by local parameters, which should be incorporated into studies of medium- and long-term coastal evolution. In the upper shoreface, the dynamics of shore-parallel bars in sandy coasts have been extensively studied, but their implications for the sediment budget remain controversial as it is unclear whether their evolution simply represents a morphological change or denotes an escape of sediment from the upper shoreface. In order to provide new knowledge to address these questions, fifteen topo-bathymetric surveys that extend from the emerged beach to 15 m water depth were carried out along 1 km of Castelldefels beach (Llobregat Delta, Barcelona, western Mediterranean Sea) during the period 2011–2022. Morphological variations on the shoreface are studied, volumetric changes are estimated and implications on sedimentary exchanges in the littoral profile are inferred. The largest morphological (volumetric) changes are caused by cross-shore displacements of the nearshore bars, usually onshore during fair-weather conditions and offshore during storms. Volumetric changes suggest that shoreline retreat and the erosion of the shallow section of the profile during the last decade provides sediment to both the distal upper shoreface and the lower shoreface. The resulting sediment budget in the profile is almost zero in absence of extreme storms, but becomes highly negative when including extreme storms events that cause a net offshore transfer of sediment from the upper to the lower shoreface and, probably, the inner shelf. The characteristics of the study area (morphology, sediments, waves, tides) and in-situ hydrodynamic measurements at the lower shoreface suggest that the main potential onshore transport mechanisms (velocity and acceleration skewness during low-mid energy event) are small, making a significant transfer of sediment from the lower shoreface towards the shallow beach area unlikely at interannual scales. Thus, the study area is an example of low-lying coastal stretch in which the potential long-term shoreline retreat caused by sea level rise cannot be fully compensated by the sediment supplied from the lower shoreface. Other mechanisms, such as sediment supplied by longshore transport, are needed to counteract this trend.

Sediment mobility over a dispersive inner shelf from combined wave and tide bed shear stress

The sediment transfers that take place between the beach and the depth of closure on the inner continental shelf play a major role in the evolution of sandy shores at different time scales. The depth of closure of the foreshore sedimentary prism, which is generally dependent on wave conditions, remains poorly constrained in the context of an internal macrotidal platform. This work aims to define and evaluate this theoretical depth, which delimits the extension of sedimentary exchanges, in particular by including the constraints applied on the sea bottom by the tidal circulation, which are very strong on the inner continental shelf of western Brittany. The use of wave (WAVEWATCH III®), tidal (MARS3D), and bottom sediment (EMODnet) databases allows us to follow an original cartographic approach to study closure depths, based on the formulations of Hallermeier (1978 and 1981) and Soulsby (1997). This cartographic approach is adapted to a spatial analysis of sediment mobility on a regional scale. First, the depth of closure shows a regional spatialisation of the seaward extension of the sediment mobility zone according to exposure to different wave climates and tidal ranges. Secondly, the method for calculating the depth of closure with the combined shear stresses (wave and tide), applied at the scale of the internal platform of western Brittany, allows the identification of three areas of movement of sedimentary particles according to critical mobility thresholds: 1) Area of no motion; 2) Area of transport and deposition; 3) Area of transport without deposition. The main contribution of this work is to propose at distinction between 2 offshore sediment motion limits, the transition to the upper plane bed (DoTupb), and the incipient motion of particle (DoTmotion). In addition, this study confirms the potential of transport and deposition of sand particles at depths >100 m in the most hydrodynamically intense areas, which implies the possibility of interconnections between hydro-sedimentary cells, through bypassing of headlands and crossing over rocky outcrops.

Geochemical and provenance heterogeneity of small mountainous river systems in Southeast China

Sediment source-to-sink processes of river systems have significant impacts on depositional environments in coastal and shelf seas and on long-term climate change. Typically, sediments at the outlets of small mountainous rivers (SMRs) are considered to represent the average composition of particles eroded from the entire river basin due to the fast sediment transfer rate and short residence time in the basins. However, this assumption may be challenged by the significant heterogeneity in sediment erosion and transport processes within the SMRs catchments. In this study, we compare the geochemical and provenance heterogeneity of two typical mountainous rivers in subtropical East Asia, the Mulanxi in Mainland China and the Zhuoshuixi in Taiwan. These two SMRs have similar monsoon climate regimes but different tectonic, geomorphic, and hydrological settings, as well as sediment routing processes. Neodymium isotopes (εNd) and stable elemental ratios of Cr/Th and Sc/Th demonstrate the remarkable intra-catchment geochemical heterogeneity of both rivers. The εNd decreases from −7.1 to −10.0 from non-tidal to tidal reaches in the Mulanxi, while it changes from −11.5 in the upper reaches to −14.1 in the lower reaches of Zhuoshuixi. Apart from the general controls of provenance lithology and weathering processes on sediment geochemical heterogeneities between these two SMRs, the intra-catchment heterogeneity of the Zhuoshuixi is mainly induced by uneven sediment mixing in the flat and low connectivity areas (accounting for ∼36.5% of the downstream area). Meanwhile, the strong tidal influence is the primary control for the intra-catchment geochemical heterogeneity of the Mulanxi sediment, and relatively long sediment residence time in the catchment also plays some role. Our study suggests that samples collected at the river mouths cannot be simply treated as representative of the basin average or fluvial end-member to the sea. The compositional heterogeneity of the SMRs and its environmental effects and responses to rapid climate change require more in-depth investigations.

Evaluating the effect of natural-artificial linear landscape elements on flow and sediment connectivity in a typical agricultural terraced catchment, China

Linear landscape elements, such as man-made ditches and road networks, play a pivotal role in the transport of water and eroded sediments. Yet very few studies have focused on the variations in drainage flow paths disturbed by artificial linear landscapes and their contribution to flow and sediment connectivity (FSC). This study utilized the index of connectivity (IC) to examine and distinguish the impact of natural and artificial linear landscape elements (i.e., natural streams, man-made ditches, and road networks) on the spatial distribution of FSC. The method was employed in a typical agricultural terraced catchment of the Honghe Hani Rice Terraces World Heritage Site of China, based on two weight factors - roughness index (RI) and Rndvic factor. The results indicate that the incorporation of the linear landscape elements for the IC calculation remarkably affected the spatial distribution of FSC. Specifically, FSC values notably increased by closing the distance to linear landscape elements within a specific threshold. Moreover, in the confluence between natural and artificial linear landscape elements, the mean value of FSC was higher compared to scenarios without any or only one linear landscape element. In comparison, the presence of road networks only improved lateral connectivity by modifying the surface flow along east-west directions, while man-made ditches significantly influenced both longitudinal and lateral connectivity to a larger degree, especially in the terraced area. This finding underscores the effectiveness of ditch constructions as management practices for the regulation of water resources and facilitating the downstream transfer of sediment. Field observations and validation confirmed that Rndvic, which incorporates vegetation variable as a weight factor in the calculation of IC, yields more accurate and reliable maps of FSC than that of RI. This study holds far-reaching significance for water resources management and landscape sustainability within terrace-protected areas, providing invaluable insights for decision-makers.

The Impact of Changes in Sea Level and East Asian Monsoon on Sediment Transport on the Sunda Shelf Since the Last Deglaciation

AbstractThe Sunda Shelf plays a key role in the sedimentation of the southern South China Sea (SCS). However, the impact of past climate changes on sediment transfer to the Sunda Shelf and the southern SCS is still unresolved. Here, we present new data on grain size, clay mineralogy, and Sr‐Nd isotopes of three marine cores, river sediments, and surface sediments of the Sunda Shelf. The results indicate that clay fractions of the central Sunda Shelf and the Gulf of Thailand derived mainly from the Mekong River and the rivers of northern Thailand since the last deglaciation. Significant changes in sediment sources are observed at 7.5 cal ka BP. From 13.3 to 7.5 cal ka BP, sediments in the Gulf of Thailand mainly originated from the rivers of northern Thailand, with contributions from the Mekong River increasing after 7.5 cal ka BP. An opposite shift is observed in the central Sunda Shelf. Such variations in the spatial distribution result from a combination of sea level and East Asian monsoon effects. After 7.5 cal ka BP, less Mekong River sediments were transported southeastwards into the southern SCS, and more sediments were gradually trapped within the delta and transported in a southwesterly direction into the Gulf of Thailand due to intense East Asian winter monsoon, which forced a strong southwestward coastal current. Our results demonstrate the important impact of East Asian winter monsoon strengthening and sea level rise in the mid‐Holocene, which can change sediment sources and transport processes on the Sunda Shelf.

The Neogene to Quaternary evolution of the Neuquén Andes broken foreland forced by tectonic, climatic and surface processes (southern Central Andes)

The Andes offer a distinctive example of the intricate interplay among climate, tectonics, and surface processes. This is exemplified by the mountain range's north-south orientation, which contrasts with the prevailing east-west wind direction. This interplay controls the uplift evolution of the broken foreland and thus the sediment transfer and erosion from mountain ranges to their forelands. The Neuquén Andes is a peculiar segment of the southern Central Andes, registering dramatic North-South variabilities in elevation, climate, and tectonic intensities established during the Neogene and Quaternary. In this study, we aimed to identify the tectono-stratigraphic evidence of the Neogene to Quaternary evolution of paleo-environments and drainage networks in the intramountainous basin of Pampa de Agua Amarga in the broken foreland of the southern Neuquén Andes of Argentina.Starting with a non-depositional and/or erosional phase during the Paleogene, the Pampa de Agua Amarga Basin underwent several phases of syn-orogenic sedimentation in the late Oligocene to early Miocene. The basin gradually shifted from a lacustrine to an alluvial depositional environment, with alluvial deposits becoming dominant in the mid-Miocene and fluvial deposits dominating in the Pliocene. A significant event occurred during the late Pliocene to early Pleistocene when coarse fluvial deposits were deposited, marking the last aggradation phase. In the early Pleistocene, the onset of incision triggered the drainage system to cut through the downstream topographic barrier. The excavation of the basin was abrupt, as evidenced by a mid-Pleistocene stepped fluvial terrace and alluvial fan that filled a large canyon across the southern end of the downstream topographic barrier.The study confirms the regional trend that Miocene basin infill is related to dry climate and high tectonic uplift, which overwhelmed the erosive power of the drainage network. The lowering of tectonic uplift intensity in the southern Neuquén Basin during the Plio-Pleistocene, along with sudden fluctuations in the global colder and wetter climate, ultimately led to the excavation of the intramountainous basin. The Westerlies Wind Belts generate high precipitation rates in the southern Neuquén Andean Cordillera, feeding the Negro River catchment in the retroarc Andean broken foreland. Consequently, the erosive power of the Negro River catchment overcame the declining tectonic uplift, causing significant erosion of the entire broken foreland and Cordillera of the southern Neuquén Andes. Conversely, more intense tectonic uplifts in the northern Neuquén Andes built a more effective orographic barriers that limited precipitation rates of both the Westerlies Wind Belt and South America Summer Monsoon, and preserved the intramountainous basins and mountain interior from erosion.

Recycling effects in detrital zircon U[sbnd]Pb signatures in a foreland basin: Identifying the multicyclic sediment sources of the Eocene-Miocene Jaca basin (southern Pyrenees, Spain)

This work deals with the provenance evolution of the mid Eocene to early Miocene clastic deposits of the Jaca basin (southern Pyrenees), which record a main drainage network reorganization during the progressive tectonic uplift of the Pyrenean orogen. We present new detrital zircon UPb data which show a Variscan-dominated detrital zircon signature for the Lutetian Hecho Group turbidites, while the overlying late Eocene to early Miocene alluvial fan sediments record a Cadomian-dominated detrital zircon signature, allowing to document a major change in the source area. Moreover, a tectono-stratigraphic cyclicity can be identified in each of the turbidite systems that conform the upper Hecho Group, featuring an enrichment of the Variscan detrital zircon signal at the base of the system, which can be interpreted as the result of an efficient sediment transfer from distant Axial Zone sources during relative sea-level lowstands, while a dilution of this signal occurs during highstands, at the top of each system, due to the reduced erosion capability of the fluvial network. Integration of detrital zircon UPb data with sandstone petrography allows for improved resolution of the source-area shifts, for discrimination between first-cycle and multi-cycle zircons, and to identify that the detrital zircon signal of the alluvial fans does not fully represent the source area configuration. This study illustrates the importance of combining petrography with detrital zircon UPb data to improve provenance reconstructions and to identify the role of sediment recycling during progressive foreland evolution.

Macroplastic fragmentation in rivers

The process of macroplastic (>0.5 cm) fragmentation results in the production of smaller plastic particles, which threaten biota and human health and are difficult to remove from the environment. The global coverage and long retention times of macroplastic waste in fluvial systems (ranging from years to centuries) create long-lasting and widespread potential for its fragmentation and the production of secondary micro- and nanoplastics. However, the pathways and rates of this process are mostly unknown and existing experimental data not fully informative, which constitutes a fundamental knowledge gap in our understanding of macroplastic fate in rivers and the transfer of produced microparticles throughout the environment. Here we present a conceptual framework which identifies two types of riverine macroplastic fragmentation controls: intrinsic (resulting from plastic item properties) and extrinsic (resulting from river characteristics and climate). First, based on the existing literature, we identify the intrinsic properties of macroplastic items that make them particularly prone to fragmentation (e.g., film shape, low polymer resistance, previous weathering). Second, we formulate a conceptual model showing how extrinsic controls can modulate the intensity of macroplastic fragmentation in perennial and intermittent rivers. Using this model, we hypothesize that the inundated parts of perennial river channels—as specific zones exposed to the constant transfer of water and sediments—provide particular conditions that accelerate the physical fragmentation of macroplastics resulting from their mechanical interactions with water, sediments, and riverbeds. The unvegetated areas in the non-inundated parts of perennial river channels provide conditions for biochemical fragmentation via photo-oxidation. In intermittent rivers, the whole channel zone is hypothesized to favor both the physical and biochemical fragmentation of macroplastics, with the dominance of the mechanical type during the periods with water flow. Our conceptualization aims to support future experimental and modelling works quantifying plastic footprint of different macroplastic waste in different types of rivers.

El Niño–Southern Oscillation (ENSO)-driven hypersedimentation in the Poechos Reservoir, northern Peru

Abstract. Although extreme El Niño events (EENEs) have always impacted hydrological anomalies and sediment transport in South America, their intensification by global warming and their association with changes in human activities and land cover after humid periods may lead to the acceleration of sediment transfers in river systems and dam reservoirs. This situation may threaten soil and water resources in arid and semiarid regions highly dependent on water originating from large dams. In this study, we investigated the sediment sequence accumulated in the Poechos Reservoir (northern Peru) and provided a retrospective reconstruction of the interactions of El Niño–Southern Oscillation (ENSO), agricultural practices and vegetation cover changes with sediment dynamics (1978–2019). To this end, a sediment core was dated and characterized by physical and chemical analyses (e.g., scanner tomography, X-ray fluorescence, particle size analysis) to estimate the evolution of sedimentation rates and changes in sediment sources during the last 5 decades. Sediment tracing results indicated the occurrence of changes in sediment sources associated with positive and negative phases of the Eastern Pacific index with a greater contribution of the lowland dry-forest area in comparison to that of the Andean area to sediment during the El Niño events (mean contribution of 76 %; up to 90 % during the coastal El Niño events (CENEs) of 2016–2017). This source contribution was mostly controlled by the stationary rainfall occurring during the EENEs in the lowland dry-forest area characterized by a low vegetation cover. Overall, after an extreme phase of ENSO, like after the EENE 1982–1983, the normal discharges and persistent sediment supplies from the middle- and upper-catchment parts led to river aggradation and the storage of substantial amounts of sediment in alluvial plains. In the absence of a significant EENE between 1983 and 1997, the large volume of sediment stored in the alluvial plains was exported by the EENE 1997–1998 resulting in an increase in sedimentation rate of 140 % after 1997 with a significant aggradation of the deltaic zone of the reservoir. In addition to the impact of extreme climate events on sediment dynamics, the development of agriculture along the riverine system after an extreme phase of ENSO increased the availability of sediments in the main channel of the rivers, easily transported by the next EENE. This study suggests that intensification of human activities associated with a higher frequency of extreme rainfall events amplified the quantity of sediment transported by the river system, which will significantly decrease the lifespan of the reservoir, which is essential to meeting the freshwater demands of the farmers and the populations living in this arid and semiarid region.

Mesoscale Shoreline Evolution on a Carbonate Sand Island: Anegada, British Virgin Islands

Anegada, the easternmost island of the Virgin Islands group (Caribbean Sea), is a low Pleistocene carbonate platform surrounded by Horseshoe Reef, the world’s third-largest fringing reef. The western part of the island consists of an extensive beachridge plain (>40 ridges). The sandy carbonate shoreline exists in three morphodynamic domains that exhibit distinctive behaviour over the 59-year study period (1953 to 2012). The northern shore is dominated by westerly longshore drift under fair-weather conditions and cross-shore sediment transport during high-energy events. Storm wave run-up and high nearshore sediment availability contribute to the construction of shore-parallel beachridges. The western end of the island is affected by refracted waves that drive strong erosion and sediment transport. This is reflected in a succession of alternating rapid shoreline recession and progradation phases over the study period. The south–central shoreline is exposed to low wave energy and is stable and colonised by mangroves. The fringing reef plays a dominant role in mesoscale shoreline morphodynamics, both as a sediment source and in wave energy dissipation. Quasi-stable points and embayments suggest a strong influence of the reef framework in controlling the shoreline’s morphology and position. Sediment transfer from the reef to the shoreline appears to take place via shore-oblique, linear sediment transport pathways that develop across the lagoon in response to the modification of incoming waves. Cannibalisation of the shoreline sediment over the past 50 years is leading to straightening of the shoreline planform. This is counter to the long-term (Holocene) development of beachridges and suggests a change from a strongly positive to negative sediment budget.

A Robust Channel Head Extraction Method Based on High‐Resolution Topographic Convergence, Suitable for Both Slowly and Fastly Eroding Landscapes

AbstractChannel networks exert a key control on drainage basins shape and dynamics, including the transfer of water and sediments throughout basins, and thus hydrosedimentary hazards. Landscape dissection by channels results from the competition between hillslope processes and channelized erosion processes such as overland flow or debris flows. In contrast to fluvial channelization, the transition from hillslopes to colluvial channels remains understudied, and high‐resolution LiDAR DEMs open new perspectives for the extensive extraction of channel heads. Several channel extraction methods exist but none is yet robust on fast eroding landscapes. Here we develop the CO2CHAIN method which identifies the hillslope to channel transition in drainage basins based on relative changes of local and upstream measures of flow convergence. We calibrate CO2CHAIN by fitting its results to channel head mapping made by geomorphologists in four contrasted basins in the United States and France with moderate to high erosion rates. Compared to two state‐of‐the‐art channel extraction methods, it fits best the experts' mapping in terms of average characteristics and variability without needing to be recalibrated and does not have to implement a drainage area threshold although it imposes a length scale threshold. This allows to revisit studies on channelization that have not yet included high erosion rate basins.

Preliminary assessment of the suspended sediment dynamics in the Sikkim–Darjeeling Himalayan river

The Sikkim–Darjeeling Himalaya region receives the highest amount of rainfall along the whole southern Himalayan margin and is known for the occurrence of extreme hydrometeorological and geomorphological events. The massive amounts of water and sediment transported each year through the mountain part of the Teesta River drainage system (∼8,150 km2)––the largest river in the region––have been severely impacted by dam construction in recent decades. The aim of the current study was to determine, for the first time in this part of the Himalaya region, the dynamics of suspended sediment transfer at a number of points distributed through the mountainous part of the Teesta River catchment prior to dam construction and preliminarily assess the impact of dam operations on the suspended sediment. Sediment sources were identified using a database of landslide inventories from 1965 to 2019, combined with visual interpretation of satellite imagery from the U.S. Corona programme and Google Earth. Hydrological and sediment data up to the second half of the 1990s were used to reconstruct the discharge and suspended sediment dynamics before direct human intervention in the river channels. The beginning and end of the construction of the reservoirs was determined by analyzing satellite images. The impact of dam operations on the suspended sediment was compiled from the available literature. The results of the current study indicate that the primary sources of sediment are landslides caused by the interaction of rainfall and road undercutting of slopes as well as channel erosion. During extreme rainfall events, the influence of deforested areas in the mobilization and delivery of sediment to the river network increases. The current analysis reveals that reconstruction of the suspended sediment dynamics should take into account the course of extreme events responsible for supplying material to the river network, as well as the long-term remobilization of already deposited sediment in the river channel. It was found that the mean suspended sediment load (SSL) following extreme rainfall, flooding, and landslides in the Teesta River catchment can be up to four times higher than its average values for the same catchment unaffected by such an event, and the effects can be observed for more than a decade afterwards. Under these conditions, the mean suspended sediment yield can reach 12,000 and up to 20,000 t/(km2·y) in individual years, which is among the highest in the Himalaya region and, indeed, the world. The construction of 13 dams in the last 30 years has disrupted the hydrological regime and sediment transport in the Teesta River catchment along 70% of its main course and largest tributaries, and this has resulted in the selective retention of coarser material in the reservoirs and a reduction in the SSL in the Himalayan piedmont. The high density of the dams suggests that further transport of suspended sediment will depend on the efficiency of the water and sediment management at the reservoirs, which may be affected by irregular natural extreme events.

Application of remote sensing monitoring to the spatiotemporal variation in debris flow activity in the catastrophic Wenchuan seismic area

Debris flows are typical compounded geohazards with long-term activity in earthquake-stricken areas. Numerous debris flows were simultaneously induced by subsequent extreme precipitation and caused serious property losses and casualties. Monitoring the dynamic variation in debris flow activity and its decay process over time is key for debris flow risk management and mitigation of the impact of debris flows. In this study, the spatiotemporal variation in debris flow activity of the Wenchuan seismic area over the past ten years was monitored based on multiperiod satellite data and field monitoring. The hillslope landslide sediment delivery to the channel gradually decreased, and the area with higher sediment transfer potential gradually changed from southern Wenchuan County to the northern area, which caused the area with high susceptibility to debris flows to gradually move towards northern Wenchuan County. Impacted by the decrease in available materials and coarsening of channel materials, the power of rainfall runoff required for driving debris flows gradually increased. This resulting debris flow is more likely to occur in this basin with a larger catchment area, longer channel length, and higher elevation difference. The changes in the debris flow activity index indicated that the debris flow activity evolves with an impulse type, and it may last for decades. The decay processes of the debris flow activity were summed up in three periods, i.e., high-activity period (2008–2015), unstable period (2015–2035), and recession period (after 2035), based on the dynamic evolution of material, hydrodynamics, and the coefficient of debris flow activity. Simultaneously, the active characteristics of debris flows in different periods were revealed, which is of great significance to the risk management of debris flows in the next period.

Critical areas for sediment delivery to the Chubut River, Patagonia Argentina: geomorphological evidence from the Sagmata pilot basin

ABSTRACT Sediment discharge events in the lower basin of the Chubut River (Patagonia, Argentina) associated with rainfall events generate serious problems for drinking water purification of more than 250,000 inhabitants and the support of livestock farming activity of about 42,000 ha in the region. Identifying the areas of potential sediment contribution to the Chubut River and the conditions necessary for erosion and sediment transfer is of vital importance to mitigate the negative impact of sediment discharge into the river and to establish water management plans. We conducted a detailed geomorphological study in a 110 km2 tributary watershed of the Chubut River (Sagmata pilot Basin), and identify potential sediment production zones. We based our analyzes on concomitant studies that indicate that the sediment remobilization is linked to the location of the drainage networks, especially in regions associated with badlands and erosional scarps formed on Paleogene continental deposits.

Modern sand provenance and transport across the western Gulf of Mexico margin

Petrographic and detrital zircon U-Pb analysis of modern beach sands and river sands from major catchments in northeastern Mexico draining to the Gulf of Mexico provides evidence for a minimum of 650 km of littoral sand transport southward from the mouth of the Rio Grande at the Mexico-U.S. border to the central part of the state of Veracruz, Mexico. Principal tracers of Rio Grande sand include: (1) quartzose composition that contrasts with lithic compositions of sand in eastern Mexico rivers and (2) detrital zircon ages with Mesoproterozoic modes at 1.8−1.5 Ga and 1.4 Ga, age groups that are typical of basement and derivative sediment of the SW United States but are uncommon to rare in Mexican river catchments. In contrast, abundant Miocene and younger grains in beach sands of Veracruz indicate primary sediment derivation from active and recently active volcanoes in the Trans-Mexican volcanic belt in central Mexico. A proportional decrease in sand of Rocky Mountain provenance with distance southward along the coast from the mouth of the Rio Grande and absence of Miocene and younger zircon grains in beaches north of rivers draining the Trans-Mexican volcanic belt indicate net littoral sand transport southward along the eastern coast of Mexico, demonstrating that wintertime shoreline-parallel surface currents rather than north-directed summertime currents dominate sediment transfer. Sand samples of Tamaulipas beaches in northeastern Mexico commonly have equal or higher proportions of U.S.-derived Mesoproterozoic zircon grains than are present in river bar sand of the lower Rio Grande and the Rio Grande delta, and thus require that littoral processes rework and incorporate coastal dune and beach sands of northeastern Mexico that are enriched in predam Rio Grande sediment. Implied coastal erosion may be related to Holocene transgression or interruption of sediment supply to the coastal sediment transport system by dams in the Rio Grande drainage basin. Such coastal erosion is impacting long-term shoreline stability and viability of the littoral environment.

STAGES OF BARRIERS FORMATION IN THE ENTRANCE GATES OF THE VOLGOGRAD RESERVOIR BAYS

The secondary processes of alongshore transport and accumulation of sediments are the consequences of reshaping the shores of the Volgograd Reservoir. Alongshore sediment transfer promoted the segregation of bays from the main water area of the Volgograd Reservoir with abrasion-accumulative barriers. Classification of the bays according to the degree of evolution of abrasion-accumulative barriers in their entrance gates is the initial stage of complex research which is necessary to reveal the main patterns of the separation process. Application of the Earth remote sensing data and geoinformation technologies is the most effective to study the process in addition to field methods. The study is based on the satellite imagery of Google Earth program and data of field research of the bays in 2008, 2010-2016 and 2019-2020. Both analytical (cartographic, graphical, mathematical methods and methods of working with satellite images) and field (geometric leveling of abrasion-accumulative barriers and spits, and bathymetric survey of bays) research methods were applied. Morphometric parameters of the entrance gates to the bays of right and left coast of the Volgograd Reservoir were measured using the satellite images of Google Earth. Expedition materials and data received from satellite images were then compared. The difference in absolute values does not exceed double standard error. This indicates the reliability of applied research method. We calculated two coefficients for classification of bays. These coefficients considered width of the bay at the entrance gate, width of the coastal shallow water area at the entrance gate and length of above-water part of a sand bar or spit. Six classes of bays were identified according to the degree of evolution of abrasion-accumulative barriers at the entrance gates: opened bays (class 1), bays at the initial stage of segregation (2), bays at the active stage of segregation (3), bays at the final stage of segregation (4), closed bays, (5) and a specific class - bays with the entrance gates subjected to anthropogenic impact (6). The bay segregation becomes more active with the expansion of the coastal shallow water area at its entrance gate. Quick overgrowth by higher aquatic, herbaceous and tree-shrub vegetation takes place under the active formation of abrasion-accumulative barriers.

Suspended sediment deposition and sediment yields at Lake Peters, northeast Brooks Range, Alaska: Fluvial‐ and lake‐based approaches

AbstractLake‐based studies can provide seasonal‐ to millennial‐scale records of sediment yield to improve our understanding of catchment‐scale sediment transfer and complement shorter fluvial‐based sediment transport studies. In this study, sediment accumulation rates at 40 coring locations in Lake Peters, Brooks Range, Alaska, over ca. 42 years, calculated using fallout radionuclides and sediment density patterns, were spatially modelled based on distance from the primary inflow and lake water depth. We estimated mean interdecadal specific sediment yield (Mg km−2 year−1) using the spatially modelled sediment accumulation rates and compared that result to fluvial‐based sediment delivery for 2015–2016 open‐channel seasons, as well as to yields reported for other Arctic catchments. Using the lake‐based method, mean yield to Lake Peters between ca. 1973 and 2015 was 52 ± 12 Mg km−2 year−1, which is comparable with fluvial‐based modelling results of 33 (20–60) Mg km−2 year−1 in 2015 and 79 (50–140) Mg km−2 year−1 in 2016 (95% confidence intervals), respectively. Although 2016 was a year of above average sedimentation, the last extreme depositional event probably occurred between ca. 1970 and 1976 when a basal layer of fine sand was deposited in a broadly distributed, relatively thick and coarse bed, which we used for lake‐wide correlation. The dual lacustrine–fluvial method approach permits study of within‐lake and catchment‐scale processes. Within Lake Peters, sedimentation patterns show decreasing fluxes down‐lake, sediment bypassing near the primary inflow, the influence of secondary inflows and littoral redistribution, and a focusing effect in the deep proximal basin. At the watershed scale, sediment yield is largely driven by intense summer rainfall and strong seasonal hydroclimatic variability. This research informs paleo‐environmental reconstruction and environmental system modelling in Arctic lake catchments.

Studying the effect of Anzali port breakwaters on sedimentation in Anzali wetland using remote sensing

The construction of new breakwaters in Anzali port has had a significant impact on the water body of the Anzali international lagoon. The Anzali wetland is under threat from sediment influx from mountainous regions, and the study used satellite image processing to demonstrate how the construction of new breakwaters impedes the natural transfer of sediment from the lagoon to the sea. The methodology employed a hybrid approach combining two methods: normal water index (MNDWI) and supervised classification (SVM) to detect sediment accumulation in the wetland water zone. Following the construction of new breakwaters in 2009, an island formed and expanded exponentially in parts of Sorkhankol Wildlife Sanctuary's water body. This phenomenon is attributed to decreased water flow caused by increased cross-section current and volume of water, creating a dam-like function against channel flow leading to the sea. Consequently, sediments and suspended loads settle in Sorkhankol's water zone, leading to an increase in island area from 0.39 hectares to over 26 hectares during the studied period. Result showed Kappa coefficients by SVM algorithm for years 2002, 2010, 2012 and 2017 which were found to be 0.76, 0.62, 0.71 and 0.86 respectively indicating that SVM outperforms MNDWI in effectively monitoring landform changes.

Spatial Patterns of Disconnectivity Explain Catchment‐Scale Sediment Dynamics and Transfer Efficiencies

AbstractWhile connectivity studies are becoming common in the Earth sciences, disconnectivity has received much less attention. Sediment storage is the direct result of sediment disconnectivity and can provide concrete evidence of the spatial patterns of disconnectivity at the catchment‐scale. In this study, we explore the catchment‐scale sediment dynamics of the Tahoma Creek watershed, a high‐gradient glacio‐volcanic landscape, within a sediment budget framework and identify and map sources of disconnectivity to determine whether they explain the spatial patterns and estimated efficiencies of sediment transfers. We found that up to 80% of the total eroded sediment is sourced from the proglacial zone. The proglacial zone is characterized by high connectivity resulting from frequent debris flows and floods, and rapidly responds to changing conditions. Down valley, however, sources of disconnectivity become increasingly more prevalent, the hillslopes become decoupled from the channel, and a majority of the eroded sediment is redeposited with as little as ∼15% reaching the outlet. The spatial distribution of sources of disconnectivity and their upslope affected areas explains, to a large degree, catchment‐scale sediment dynamics and sediment transfer efficiencies and is in close agreement with quantitative connectivity estimates. We find that steep, glaciated watersheds are predominantly disconnected over human timescales and suggest that disconnectivity is the dominant state of landscapes over most timescales of interest. Mapping sources of disconnectivity provides a straightforward and concrete approach to estimating system disconnectivity and can increase confidence when paired with quantitative indices.

Effects of human-induced riverine sediment transfer on deposition–erosion in the South Passage of the Changjiang (Yangtze) delta

Deltaic channels, as the essential part in system of river deltas where river and ocean connect, are influenced profoundly on its deposition and erosion processes, by changes of riverine sediment due to human activities from catchment to mouth of large rivers and sea-level rise worldwide. Here, based on a series of hydrological, sedimentary and morphological records in the main outer channel South Passage (SP) of the river-tide dominant Changjiang (Yangtze) Delta (CJD) for more than half a century, regional deposition–erosion process and the implication mechanism were examined. The results showed that fluvial sediment supply declined by over 70% stepwise during the past decades and local suspended sediment concentration in the SP reduced by half within recent years. Correspondingly, three distinct stages of morphodynamic process came out one after another, which were phases of rapid deposition (1959–1979), moderate deposition (1979–1997) and dramatic erosion (1997–2021), respectively. Channel and shoal had asynchronous performance during this deposition–erosion transition, especially after 1979, when channel entered a rapid erosion period earlier after a stable volume period, while shoal suffered slow erosion after high-speed deposition. Moreover, the current erosion phase was furtherly explained as two main modes by the Empirical Orthogonal Function analysis, accounting for 61% and 14%, respectively. The dominant mode describes the continuous scouring in channel contributed by transfer in riverine sediment regime, consisting of the reducing upstream sediment, local increasing flow diversion, dredging activities and sea-level rise. The second mode suggests decadal shift from deposition to slight erosion of shoal zones, which was also adjusted to episodic events and local engineering projects like shoal embankment and reclamation. It’s predictable that the SP would constantly suffer long-term erosion under riverine sediment reduction, sea-level rise and artificial waterway regulation, together with aggradation of the fringing shoals by reclamation. This highlights channels in the river deltas are faced with the erosion risk caused by anthropogenic activities, which calls for compelling attention.