Coarse Sediment Research Articles

Long-term geomorphic adjustments following the recoupling of a tributary to its main-stem river

River restoration and rehabilitation projects are widespread, but rarely include the data needed to fully evaluate if they are successful in achieving their goals or how long the process of readjustment takes before a new ‘recovered’ regime state is reached. Here we present a seven-year post-project dataset detailing the morpho-sedimentary responses of a river to the reconnection of a formerly diverted tributary, and relate observed changes to conditions in the river prior to the reconnection. We describe changes in the tributary and main-stem channels, including changes in channel planform, morphology, and the export of coarse and fine sediment from the tributary to the main-stem river. We use the data to develop a conceptual model of the system's response to the reconnection.Marked geomorphic changes occurred within the first two years after the reconnection. Changes during this ‘shock phase’ included dramatic erosion and subsequent deepening and widening of the tributary channel, rapid development of a confluence bar and an increase in fine sediment delivered to the main-stem. After this shock phase, and despite the continued occurrence of high magnitude flow events, the rate of geomorphic change in the tributary began to decrease, and the rate of growth of the confluence bar slowed. Fine sediment volumes in the main-stem also decreased steadily. After an adjustment phase lasting a total of approximately 4.5 yr (including the initial 2-yr shock phase), the tributary to mainstem system appeared to reach a new dynamic equilibrium that we consider the adjusted regime state. This new regime state was characterised by, among other things, an increase in geomorphic heterogeneity in the tributary and main-stem channels.Changes in both fluvial processes and forms indicate that within 4.5 yr the project was successful in achieving its goal of augmenting sediment and increasing geomorphic heterogeneity. Our conceptual model of adjustment mirrors that developed by Petts and Gurnell (2005), with the river passing through a complex and dynamic adjustment phase before reaching a new regime state. However, unlike the responses to impoundment represented by Petts and Gurnell, our model of river response to rehabilitation charts increases in dynamism and heterogeneity.

Sediment source determination for a series of connected check dams in an agricultural catchment in the Chinese Mollisol region

The composite fingerprinting approach is valuable in sediment source identification at different temporal and spatial scales. However, few studies have estimated watershed sediment source connections and transport impacted by multiple check dams. This is due to the complexity of particle sorting under flood discharge practices. Here, we attempt to identify sediment sources with three connected check dams in an agricultural Mollisol catchment in Northeast China based on optimal fingerprints screened from different size fractions (i.e., <10, <63, and <1000 μm). The results showed consistent sediment contributions based on fine particle size ranges (i.e., <10 and <63 μm) but an inconsistent contribution based on a coarse particle size range (i.e., <1000 μm), regardless of the particle size or the organic corrections applied. Sediment deposited in check dams No. 1 and No. 2 was mainly from hillslopes (cropland) (>66.7 %), while sediment in check dam No. 3 was from its adjacent upstream check dam (i.e., No. 2; >60.5 %) based on optimal fingerprints screened from <10 and <63 μm particle size ranges. However, when fingerprints were screened from a coarse particle size (<1000 μm), sediment in all three check dams was mainly from gully slopes (>79.0 %), regardless of the specific surface area (SSA) of particles or the soil organic carbon (SOC) correction factors used in the model except for SOC correction for check dam No. 2. Conversely, sediment was mainly derived from hillslopes when fingerprint values were corrected using SSA and SOC, except that no optimal fingerprints were selected. This indicated the feasibility of sediment source discrimination based on the composite fingerprinting approach for sediment source identification in catchments with a series of connected check dams under the condition that particle fractions impacted by check dams are relatively weak. However, optimal fingerprints screened from a relatively wide range of coarse particles caused divergent results regardless of the particle size or the organic correction factors used in model estimation or in fingerprint values. Further studies are necessary to explore the reliability of the composite fingerprinting approach for sediment source tracing under a series of connected check dams, where coarse sediment is selectively deposited and fine sediment is massively discharged under flood discharge practices.

Suspended Sediments in Environmental Flows: Interpretation of Concentration Profiles Shapes

In environmental flows, field and laboratory measurements of suspended sediments show two kinds of concentration profiles. For coarse sediments, a near-bed upward convex profile is observed beneath the main upward concave profile. In this study, we consider two 1-DV models, namely, the classical advection–diffusion equation (ADE) based on the gradient diffusion model, and the kinetic model. Both need sediment diffusivity, which is related to the eddy viscosity, and an y-dependent β-function (i.e., the inverse of the turbulent Schmidt number). Our study shows that the kinetic model reverts to the classical ADE with an “apparent” settling velocity or sediment diffusivity. For the numerical resolution of the ADE, simple and accurate tools are provided for both the sediment diffusivity and hindered settling. The results for the concentration profiles show good agreement with the experimental data. An interpretation of the concentration profiles is provided by two “criteria” for shapes. The main for steady open-channel flows shows that the shape of the concentration profiles in the Cartesian coordinate depends on the vertical distribution of the derivative of R (the ratio between the sediment diffusivity and the settling velocity of the sediments): dR/dy &gt; −1 for the upward concave concentration profile while dR/dy &lt; −1 for the near-bed upward convex profile. A generalization is proposed for oscillatory flows over sand ripples, where the time-averaged concentration profiles in the semi-log plots are interpreted by a relation between the second derivative of the logarithm of the concentration and the derivative of the product between the sediment diffusivity and an additional parameter related to the convective sediment entrainment process.

Chinook Salmon habitat evolution following river restoration, drought, and flood

How rivers restored for aquatic biota such as Pacific Salmon (Oncorhynchus spp.) will evolve under shifting management and climate regimes is unknown. To inform this, we tracked the evolution of a highly impacted, regulated river reach following habitat restoration and subsequent drought and flood hydrology using a suite of data to better understand how created habitat evolves over time. Topographic change detection, riffle creation and persistence, substrate, and Chinook Salmon spawning and rearing habitat were evaluated for the three epochs. Sediment transport regimes and velocity outputs from the numerical flow model were used to interpret channel change associated with the flood season the site experienced. Salmon spawning observations and habitat suitability modeling demonstrated that habitat improved following restoration for both salmon spawning and rearing. Chinook Salmon spawning activity and the relative site utilization compared to escapement increased post Project. These benefits were largely maintained during drought and flood events, despite an absence of upstream coarse sediment supply. We hypothesize this was because the restoration design incorporated riffle-pool maintenance theories and the use of emergent islands that served as a local sediment source. Extrapolations of bioturbation by spawners suggest that if population targets for the river are met, topographic change due to spawning activity could exceed that caused by river flow under drought conditions and provide a modest contribution during flood years. Thus, this study demonstrates that river restoration can not only improve physical habitat, but also engage ecosystem engineers such as spawning salmonids to contribute to future habitat evolution.

Štěrky na rozvodí Dyje a Pulkau jižně od Znojma (Česko–Rakousko): nové poznatky ve srovnání s dosavadním stratigrafickým zařazením

A thin veneers of coarse gravel deposits (clast size up to &gt; 15 cm) are preserved on many summits of the Dyje–Pulkau watershed upland on the Carpathian Foredeep surface near the Bohemian Massif in the area, where the Waitzendorf fault parallels the boundary between both the large geological units. Related rim of the latter unit is there topographically manifested by the current prominent marginal slope mostly developed in granitoids of the Dyje Massif. In the existing maps and corresponding explanatory notes the northwestern occurrences of the gravel were considered, without direct stratigraphic evidence, as marine deposits of the Lower Badenian or uppermost Karpatian age (Lower/Middle Miocene transition). This paper revises the assumed genesis and stratigraphic position of the gravel based on pebble grain size and petrography analysis, assessment of geomorphological setting, and comparison with other gravel deposits in the vicinity characterized by some similar properties. The study of pebble material on the watershed upland revealed an existence of two adjacent WNW–ESE trending gravel belts of different petrography: the southern with only dominant quartz-rich rocks and the quartz-rich northern but with a high portion of the Dyje Massif rocks. Gravel characteristics and its position above fine-grained Carpathian Foredeep sediments in the basement deposited in the Lower/Middle Miocene transition period (lower stratigraphic limit) indicate a later terrestrial origin of both the gravel belts by two adjacent streams flowing from the WNW towards the ESE and largely redeposi­ting coarse material eroded in older layers at former margin of the foredeep basin. In the southern and northern surroundings of the watershed upland a number of other gravel sites are preserved near or within the marginal slope whose coarse pebbles also overlay fine-grained basement clastic sequences of the Carpathian Foredeep. Their mutually different petrographic properties also indicate dissimilar source areas within marginal part of the basin presumably located in the WNW or NW, thus supporting quite uniform material transport direction in many subparallel traces. The general regional transport seems to be largely interrupted by a renewed activity of the Waitzendorf fault system predisposing the Bohemian Massif uplift against the current Carpathian Foredeep. A related strong stream incision into the uplifted surface included a newly created SW–NE reach of the Dyje river within the marginal slope between the Šobes meander and the town of Znojmo whose origin presumably started in the (Lower) Pliocene (higher stratigraphic limit) based on the supposed age of sedimentary remnants preserved within higher parts of the corresponding valley section. Thus the deposition of gravel at the Dyje–Pulkau watershed finished before or shortly after the uplift and the valley incision began. Genesis and stratigraphic position of the focused coarse sediments is likely different from those in the previous considerations.

Facies architecture of the Plio-Quaternary alluvial fan deposits from south-eastern margin of the Saïss foreland basin (Morocco): Paleoclimatic and neotectonic implications

Eight Plio-Quaternary alluvial fans from south-eastern margin of the Saïss foreland basin were the subject of a thorough sedimentological study based upon detailed facies analysis. This study allowed distinguishing 16 sedimentary facies. The typology of the latter, their spatial distribution and sedimentary organization afforded the classification of the studied fans into three groups. Group 1 is dominated by non-cohesive debris flow and cohesive to very poorly-sorted blocky conglomerate deposits that are associated with silt-clayey and calcrete. The setting up of the deposits of this group occurred in a tectono-karstic depression whereby a WNW progradation of the deposits and an important incision into the previous consolidated deposits would have been controlled. Group 2 is characterized by a predominance of the muddy fraction, presumably linked to the large surface area of the watershed and the river activity. Group 3 is dominated by coarse deposits with rare mudflows interpreted to be the direct consequence of an important neotectonic activity which is expressed by localized incremental pulses of the Agourai-El Hajeb-Ain Cheggag faults system and Middle Atlas directional faults (i.e., NE-SW) along toe fan during the Plio-Quaternary period. Groups 2 and 3 are also characterized by deposits whose the related processes are dominated by cohesive and non-cohesive debris flows, mud-rich debris, channelized debris flows and non-cohesive flows, hyper-concentrated flows and sheet-flood flows. The morphogenesis of these alluvial fans and the emplacement of their deposits are neotectonic- and climate-controlled. Tectonics have played a major role in the rejuvenation of the Middle Atlas relief and, through controlling the base-level, created the space available for the establishment and development of alluvial fans onto the south-eastern margin of the Saïss basin. This extensive tectonics has resulted in normal faultings and layer tiltings. The climate played an important role in the formation of facies by controlling (i) the mechanical properties of paleoflows, (ii) sedimentary dynamics and (iii) the formation of paleosols and calcrete.

Variations in the concentration, source and flux of polycyclic aromatic hydrocarbons in sediments of the Pearl River Estuary: Implications for anthropogenic impacts

Variations in the distribution, source composition, mass inventory and burial flux of polycyclic aromatic hydrocarbons (PAHs) in surface sediments from the Pearl River Estuary (PRE) collected in 2011 and 2019 were analyzed to investigate the influence of the anthropogenic activities. Total concentrations of 16 priority PAHs in 2019 (200.40 ± 188.86 ng g−1 dry weight on average) were at the medium level among global bays/estuaries/coastal areas. In 2019, PAH concentrations have decreased by about 50% compared to 2011 and the dominant composition has changed from low- to high-molecular-weight PAHs. The qualitative and quantitative source apportionment analysis indicates that the dominant source of PAHs has shifted from petroleum (40.33%) in 2011 to traffic emission (44.17%) in 2019. The source variation in the PRE can be attributed to the transformation of the energy source structure from petrogenic to pyrogenic in the Pearl River Delta. The estimated PAH mass inventory of the top 5-cm sediment was 38.70 metric tons in 2019, which was about 41 metric tons lower than that in 2011. The average deposition fluxes have dropped from 418.91 ± 261.02 ng cm−2 yr−1 in 2011 to 215.52 ± 246.63 ng cm−2 yr−1 in 2019. The decreasing PAH concentration is related to the sediment coarsening and decline of total organic carbon. These findings in the PRE can be applied to other estuarine environments influenced by anthropogenic activities.

Novel sediment sampling method provides new insights into vertical grain size variability due to marine and aeolian beach processes

AbstractIn sandy beach systems, the aeolian sediment transport can be governed by the vertical structure of the sediment layers at the bed surface. Here, data collected with a newly developed sand scraper is presented to determine high‐resolution vertical grain size variability and how it is affected by marine and aeolian processes. Sediment samples at up to 2 mm vertical resolution down to 50 mm depth were collected at three beaches: Waldport (Oregon, USA), Noordwijk (the Netherlands) and Duck (North Carolina, USA). The results revealed that the grain size in individual layers can differ considerably from the median grain size of the total sample. The most distinct temporal variability occurred due to marine processes that resulted in significant morphological changes in the intertidal zone. The marine processes during high water resulted both in fining and coarsening of the surface sediment. Especially near the upper limit of wave runup, the formation of a veneer of coarse sediment was observed. Although the expected coarsening of the near‐surface grain size during aeolian transport events was observed at times, the opposite trend also occurred. The latter could be explained by the formation and propagation of aeolian bedforms within the intertidal zone locally resulting in sediment fining at the bed surface. The presented data lays the basis for future sediment sampling strategies and sediment transport models that investigate the feedbacks between marine and aeolian transport, and the vertical variability of the grain size distribution.

Who Was Buried at the Petit-Chasseur Site? The Contribution of Archaeometric Analyses of Final Neolithic and Bell Beaker Domestic Pottery to the Understanding of the Megalith-Erecting Society of the Upper Rhône Valley (Switzerland, 3300–2200 BC)

Abstract The Petit-Chasseur megalithic necropolis is a key archaeological context for analyzing the social and ideological changes at the end of the Neolithic in the Alpine region of Central Europe. The link between the funerary monuments and settlement sites was established by means of ceramic archaeometric analysis. Domestic pottery from settlement sites were thoroughly characterized using multiple spectroscopic and microscopic techniques. Twelve ceramic fabrics were identified along with three types of clay substrate: illitic, muscovitic, and kaolinitic. Reconstructed paste preparation recipes largely involved the tempering of the raw clays with crushed rocks or coarse sediments. Types of raw material were not picked up randomly but were selected or avoided due to their particular compositional properties and attest to the exploitation of glacial, gravitational, eolian, and fluvial deposits. Compositional correspondence between ceramic grave goods and domestic pottery allowed identification of a link between the megalithic tombs and settlement sites, thus providing new data contributing to the investigation of the social dimension of monumental burials. Ceramic grave goods were revealed to be intertwined with the social instability affecting the 3rd millennium BC communities of the Upper Rhône Valley.

Effects of sediment fractions on slump-flow parameters of fine- and coarse-sediment suspensions

• Slump-flow parameters (slump and spread) of fine- and coarse-sediment suspensions are measured using a mini-slump cone. • Effects of fine- and coarse-sediment fractions on the slump-flow parameters are analyzed and empirically formulated by power-law and exponential relations, respectively. • The single- and double-layer models of Roussel and Coussot [22] and Pierre et al. [21], respectively are generalized for a conical-shaped mould in the range of 0 < α ≤ 1 . • The dimensionless slump and spread of fine- and coarse-sediment suspensions are strongly correlated and their empirical relation was compared to the theoretical relations. • The slump-flow parameters and Bingham yield stress exhibit good correlations in both theoretical and empirical analyses, indicating that the slump-flow test may be used to indirectly evaluate the rheology of sediment suspensions. Slump-flow tests on concentrated fine-sediment suspensions (mixtures of clay-silt-water) and coarse-sediment suspensions (mixtures of coarse sediments and a specified fine-sediment suspension) were performed to investigate the effects of sediment fractions on the slump-flow parameters (slump and spread). The slump and spread of fine- and coarse-sediment suspensions decrease with an increase in the sediment fractions, and their empirical equations were proposed. Both experimental and theoretical results show that the slump and spread of sediment suspensions are strongly correlated. Theoretical relations of the Bingham yield stress and slump-flow parameters were also presented for comparison. The slump-flow parameters exhibit a strong correlation with the rheological parameters measured using a conventional rheometer, indicating that the rheological parameters of the tested sample could be indirectly evaluated by a simple slump-flow test.

Detection of Groundwater Table by Using Ground Penetrating Radar in Two Selected Sites/Northern Iraq

A non-damaging geophysical measurement technique test method ground penetrating radar (GPR) was carried out successfully in two sites in the middle and north of Iraq in order to investigate the feasibility of detecting the shallow underground water level in both selected sites. The results show that the groundwater depths in Baiji site were between 0.95m, and 1.2m, while in Hammam AL-Aleel site were between 1.0m to 1.1m near the river. It was also noticed in Hammam AL-Aleel site that the GPR image showed the appearances of dramatically and clear dissolving features that sometimes coincide with the level of groundwater which was approximately about 4m depth to the west of Northern Thermal Power Plant (NTPP), due to the existence of Fatha formation; while in the east of (NTPP) there was no solubility features due to the absence of Fatha formation and the presence of quaternary coarse sediments. This technique has been proved to be an effective detection method for underground water level and can serve as a reference for future application using the dependent physical property of permittivity and conductivity in engineering site investigation, hydrogeological investigations, and the detection of subsurface cavities.

Environmental shifts in and around Lake Pannon during the Tortonian Thermal Maximum based on a multi-proxy record from the Vienna Basin (Austria, Late Miocene, Tortonian)

The Neogene Lake Pannon was the largest lake that ever existed in Europe. It attained its greatest extent during the Tortonian Thermal Maximum. For the first time, results from a detailed lake record documenting about 85 kyr of Late Miocene time in a continuously recovered, 60-m-long, clay-rich core of Lake Pannon are reported. This record includes the transition from the lake's maximum transgression into its highstand at around 10.4 Ma. The environmental development of Lake Pannon during its maximum extent is interpreted based on integrated paleontological, sedimentological, mineralogical and geochemical data. The maximum extent coincided with stable sedimentation of clay, little influx from the hinterland, low surface productivity and severe bottom-water anoxia. The clay mineralogy of the lower part of the core points to prevailing chemical weathering based on the illite/smectite ratios. Distinct Fe, Mn and Ba enrichments are interpreted to have formed close to sulfate-methane transition zones during the maximum flooding. The highstand phase was marked by rapid environmental shifts with frequent phases of well‑oxygenated bottom waters. These phases are reflected by rich benthic communities including stenohaline tunicates. The increased input of detritic kaolinite suggests a shift towards physical weathering and higher precipitation coinciding with a shift in the provenance of clay minerals.Increasing amounts of nutrients stimulated surface water productivity and nannoplankton blooms. Despite the offshore position of the core at ∼8 km from the mountainous ranges of the Alps, strong fluvial input is reflected from 32.5 to 30.3 m by coarser sediment and the occurrence of terrestrial and freshwater molluscs. The Rhenodanubian Flysch Unit was the main source of the siliciclastics of the core and was drained by the Paleo-Wien river. Drainage from the Calcareous Alps was limited to an exceptionally strong fluvial event and related deposits, which documents the presence of a second river in the southwest, which might represent the Paleo-Liesing.The dominance of smectite throughout the core suggests a temperate climate with distinct seasonality during the Tortonian Thermal Maximum. In view of the autochthonous ascidian sclerites in three samples, and assuming generally similar ecological requirements for both Pannonian and modern tunicates, we conclude a polyhaline salinity for Lake Pannon around 10.4 Ma.

Spatial distribution, abundance, seasonality and environmental relationship of amphioxus in subtropical Hong Kong waters

Amphioxus are a small group of cephalochordates inhabiting shallow-water coastal areas in both tropical and temperate oceans. In Hong Kong, only one study of the species composition and distribution of amphioxus was conducted in the 2000s. The present study aimed to provide up-to-date information on the diversity, seasonal abundance and distribution of amphioxus and identify environmental factors that might play a role in structuring their distribution. Benthic grab samples were collected from 23 sites spanning the eastern, southern, and southwestern waters of Hong Kong in 2019 (dry season) and 2020 (wet season). Samples from 13 sites yielded at least one individual of amphioxus, including several sites that were not covered in the previous study. A total of 1845 specimens belonging to three species of Branchiostoma were recorded, including B. belcheri, B. japonicum and B. malayanum. Among the 13 sites, amphioxus density varied from 14 to 618 individuals m−2 in the dry season and 4 to 322 individuals m−2 in the wet season. A high density of amphioxus (> 200 individuals m−2) was found at Po Toi O, Pak Lap Wan and Tai Long Wan. The three species of amphioxus typically co-inhabited these sites, with B. belcheri, B. japonicum, and B. malayanum accounting for 72.63%, 16.26%, and 11.11% of the total abundance, respectively. The three species all preferred shallow-water sites with coarse sediment and low organic matter content. Comparison of the population size structure between the two seasons revealed higher percentages of juveniles in the dry season, indicating reproductive seasonality in these species.

Distribution and Accumulation of Heavy Metals in Marine Sediment from Marudu Bay, Sabah

This study aims to analyse the distribution and factors that control the accumulation of heavy metals in marine sediment from Marudu Bay, Sabah. The sediment samples originated from the various types of rocks, namely ultrabasic rock, basic rock, and chert of ophiolite sequence, and sedimentary rock of the Kudat Formation. A total of 20 sediment core samples were systematically sliced for physico-chemical analysis such as pH value, organic matter (OM), and particle size distribution (PSD). Seven heavy metals are analysed in this research, namely cobalt (Co), chromium (Cr), copper (Cu), manganese (Mn), nickel (Ni), vanadium (V), and zinc (Zn) which is measured using the ICP-OES instrument. Descriptive statistics were used to study the distribution and accumulation of heavy metals from two main stations, namely Sg Karang Station (ST) and Kg Tampakan Station (SK). The results from both stations showed various levels of heavy metal concentration. The average concentration of Mn is between 2.19 mg/kg - 94.77 mg/kg and followed by Cr (0.87 mg/kg - 21.11 mg/kg). For Ni, Zn, Cu, V, and Co, the concentration range were between 0.28 mg/kg - 11.48 mg/kg, 0.94 mg/kg - 6.95 mg/kg, 0.55 mg/kg - 6.01 mg/kg, 0.64 mg/kg - 3.77 mg/kg, and 0.02 mg/kg - 0.85 mg/kg respectively. The result of correlation analysis showed the significant negative relationship between pH with Co, Cr, Ni, Mn, and Zn indicated the increasing concentration in acidic condition. A strong negative correlation between percentage of sand and Co, Cr, Mn, and Ni indicated the decreasing concentration in coarse sediment particle size. However, there was a strong positive correlation between percentage of sand and V due to the association in the carbonate minerals. The Kruskal-Wallis tests showed there were no significant means difference of the percentage of heavy metals based on sample depth and the distance from the shoreline except for V and Mn.

Planning of Vegetative Structures for Coastal Protection Based on Analysis of the Results of Coastal Substrate in Palu Bay

An earthquake followed by a tsunami occurred on September 28, 2018, in Central Sulawesi. National Disaster Management Agency recorded that 2,113 people died from the earthquake and tsunami, spread over 1,703 people in Palu City, 171 people in Donggala Regency, 223 people in Sigi Regency, 15 people in Parigi Moutong Regency, and Pairskayu Regency with a total of 15 people. 1 person. According to satellite imagery data obtained [2], damage to buildings that occurred in Palu City reached 2,403 buildings and caused the paralysis of Palu City from various aspects, around 70,000 people were accommodated in temporary shelters. Structural mitigation efforts to reduce the impact of damage from natural disasters can be done naturally or artificially. One of the natural structural mitigation efforts in the coastal area of ??Palu City is the creation of a coastal green belt or generally called a Greenbelt. Planting coastal vegetation and mangroves and maintaining existing coastal forest ecosystems is a disaster mitigation effort. Coastal forest ecosystems and mangroves have strong and sturdy root systems that can grip the deepest soil layers. The canopy is flat and dense, and dense at all times, making coastal forests and mangroves an ideal natural protection against the threat of disasters in coastal areas. The purpose of this research is to plan the formation of coastal forests (Planning Vegetative Structure for Coastal Protection) in Palu City Bay. The method used in this research is a descriptive method, namely by field observation, which is carried out to determine the existing condition of vegetation in the coastal area of ??Palu Bay. Based on the results of the analysis, at 23 measurement points, it was found that the thickness of the fine sediment at the bottom of the water ranged from 1-10 cm, while the results of the analysis of the thickness of the coarse sediment ranged from 1-26 cm. The sediment population in Palu City has the characteristics of Gravel (gravel) and Sand (sand). The potential content of TSS in the water column reaches 188 mg/L.

Multi-temporal analysis of morphological changes in an Alpine proglacial area and their effect on sediment transfer

Proglacial areas in high-mountain environments are among the most dynamic landscape zones in terms of morphological, sedimentological, and hydrological changes. In fact, in such areas both glacial and paraglacial dynamics exert a strong control on water fluxes (and thus on bedload transport capacity) and on sediment supply. Because of the rapid changes undergoing in these environments, the understanding of the dynamics of sediment transfer and the prediction of how this will change in future still remain a challenge. In this study, we used four different high-resolution topographic surveys to quantitatively analyse the spatio-temporal patterns of sediment transport that occurred in the proglacial area of the Sulden glacier (South Tirol, Italy). The topographic surveys covered the period 2013–2019 and – by building DEMs of difference (DoDs) – we calculated the volumes of erosion and deposition occurring at the glacier terminus and along its outflow channels. Our results indicate that, within the analysed time-period and for different areas, erosion and deposition generally show similar values, suggesting that the analysed proglacial areas has been acting both as a sediment trap and as a sediment source for the downstream river reaches. In addition, the results indicate a complex morphological dynamics, which have strongly impacted coarse sediment connectivity in the upper catchment. In particular, high temperatures and the recent and rapid glacier melt, have promoted a direct control on the structural connectivity within the proglacial area. Morphological changes have increased or decreased sediment connectivity depending on pre-existing morphological features. In contrast, extreme precipitation events, both in term of rainfall and snowfall, have locally and temporally increased the functional connectivity, sometimes leading to long-term modifications in the proglacial area. Overall, in the analysed time-period sediment transfer has been extremely dynamic, suggesting that sediment in the downstream river channel may have been supplied with irregular pulses associated with the morphological changes taking place in the proglacial area.

Sediment transport and morphological responses of a silty coast to a cold front event in the southwest Bohai Bay of China

Silty coast, as a transitional state between muddy coast and sandy coast, possesses a considerable percentage of the overall coast in China. Huanghua-Binzhou coast in the southwest Bohai Bay in the northeastern China is a typical silty coast which is vulnerable to cold fronts when its seabed is prone to suffer suddenly drastic erosion and deposition due to the sediment there with relatively low incipient velocity and high settling velocity. In this study, a multi-sediment fraction model was established and two-way coupled with the wave-tide-surge model to investigate the responses of the sediment transport and morphodynamics of Huanghua-Binzhou coast to a cold front event during 10–13th Oct. 2003. The model results demonstrate that three sediment fractions, i.e. mud, silt and sand, showed different responses to the storm due to their different spatial percentages and distinct physical properties. The silt fraction, as the primary fraction, played a leading role in the suspension and transport of the total sediment, and showed a pattern of “deposition-erosion-deposition” in the cross-shore direction like the total morphological change. The fine sediment was transported westward and offshore during the storm, which indicated the sediment coarsening in the study area. The depth-induced wave modulation considerably enhanced the resuspension ability of the nearshore waves for sediment and thus played a critical role in intensifying the erosion. The Huanghua waterway siltation mainly resulted from the resuspension of the offshore sediment by the strong wind waves and its westward transport by the wind-induced currents during the storm. The construction of two long jetties in 2006 can significantly reduce the deposition in the waterway by 75%, and the additional large-scale construction in 2016 can further lessen the waterway siltation by intercepting the westward sediment transport and reduce the suspended sediment concentration by 30% by the land reclamation in the study area.

Quantitative regional observations of gravel and bedrock influence on beach morphologies

Geological features such as underlying bedrock and coarse sediment layers/deposits are known to influence sandy beach morphology, however existing observations are often spatially limited, qualitative, and/or focused on limited geological feature types. Using mobile terrestrial LiDAR data collected twice yearly from 2017 to 2021, this study quantitatively examines the influence of intermittently and/or semi-permanently exposed gravel deposits and bedrock on seasonal subaerial beach elevations along ~40 km of coast in northern San Diego County, California. Both seasonal beach elevations, surface gravel/bedrock exposure, and modeled nearshore wave conditions varied considerably in space and time. Sandy beaches with limited bedrock/gravel exposure generally had relatively large typical winter-erosion and summer-accretion elevation changes, while beaches with frequent bedrock exposure often had relatively small elevation changes and occasionally exhibited localized seasonal elevation change reversals (e.g. winter-accretion). Beaches with surface gravel often had relatively large foreshore elevation changes compared to the upper beach, and exhibited upper beach elevation change reversals (e.g. winter-accretion). The results also suggest gravel and bedrock influences can be interrelated. Localized seasonal elevation change reversals were also observed on beaches with large alongshore variation in radiation stress near submarine canyons. This study highlights the utility of spatially large-scale and concurrent quantitative mapping of beach elevation and multiple geologic feature types.

When knickzones limit upstream transmission of base-level fall: An example from Kaua‘i, Hawai‘i

AbstractA threshold drainage area limits fluvial transmission of base-level fall and may be expressed in the form of a waterfall or a series of waterfalls, defined here as a knickzone. Knickzones on the west coast of Kaua‘i, Hawai‘i (USA), exhibit evidence of a threshold drainage area. Eighteen (18) of the 25 knickzones in our study area are located at the coast or a tributary junction, have a drainage area &amp;lt;1.5 km2, and have been stationary for at least 1.5 m.y. The other seven knickzones are located &amp;gt;1 km upstream from the coast or nearest tributary junction and range in drainage area from 1 to 5.5 km2. Both sets of knickzones limit incision relative to canyons without knickzones. Field observations show strong ‘a‘ā flows and dikes always crop out at the lip of knickzones, suggesting these resistant rocks and coarse sediment generated from them act to inhibit knickzone migration. A model incorporating flood records and channel conditions above knickzones shows thresholds of coarse sediment entrainment are never exceeded below 1 km2. Our results demonstrate knickzones on the west coast of Kaua‘i are enduring features explained by resistant lava flows and physical limits in bedrock incision.

Implications of the loess record for Holocene climate and human settlement in Heye Catchment, Jiuzhaigou, eastern Tibetan Plateau, Sichuan, China

AbstractWe examine the Holocene loess record in the Heye Catchment on the margins of the Tibetan Plateau (TP) and China Loess Plateau (CLP) to determine: the region to which the Heye Catchment climate is more similar; temporal change in wind strength; and modification of the loess record by mass wasting and human activity. Luminescence and radiocarbon dating demonstrate loess deposited in two periods: &gt;11–8.6 ka and &lt;5.1 ka. The 8.6–5.1 ka depositional hiatus, which coincides with the Mid-Holocene Climatic Optimum, is more similar to the loess deposition cessation in the TP than to the loess deposition deceleration in the CLP. Grain-size analysis suggests the Heye loess is a mixture of at least three different grain-size distributions and that it may derive from multiple sources. A greater proportion of coarse sediments in the older loess may indicate stronger winds compared with the more recent depositional period. Gravel incorporated into younger loess most likely comes from bedrock exposed in slump scarps. Human occupation of the catchment, for which the earliest evidence is 3.4 ka, postdates the onset of slumping; thus the slumps may have created a livable environment for humans.