Sediment Mass Research Articles

Watershed Suspended Sediment Supply and Potential Impacts of Dam Removals for an Estuary

Observations and modeling are used to assess potential impacts of sediment releases due to dam removals on the Hudson River estuary. Watershed sediment loads are calculated based on sediment-discharge rating curves for gauges covering 80% of the watershed area. The annual average sediment load to the estuary is 1.2 Mt, of which about 0.6 Mt comes from side tributaries. Sediment yield varies inversely with watershed area, with regional trends that are consistent with substrate erodibility. Geophysical and sedimentological surveys in seven subwatersheds of the Lower Hudson were conducted to estimate the mass and composition of sediment trapped behind dams. Impoundments were classified as (1) active sediment traps, (2) run-of-river sites not actively trapping sediment, and (3) dammed natural lakes and spring-fed ponds. Based on this categorization and impoundment attributes from a dam inventory database, the total mass of impounded sediment in the Lower Hudson watershed is estimated as 4.9 ± 1.9 Mt. This represents about 4 years of annual watershed supply, which is small compared with some individual dam removals and is not practically available given current dam removal rates. More than half of dams impound drainage areas less than 1 km2, and play little role in downstream sediment supply. In modeling of a simulated dam removal, suspended sediment in the estuary increases modestly near the source during discharge events, but otherwise effects on suspended sediment are minimal. Fine-grained sediment deposits broadly along the estuary and coarser sediment deposits near the source, with transport distance inversely related to settling velocity.

Macrofaunal diversity and community structure of the DeSoto Canyon and adjacent slope

Northern Gulf of Mexico canyons are centers of organic matter accumulation and biodiversity, but studies of their finer-scale (sub-100 km) ecological patterns are scarce. Detailed sampling of macrofauna within the DeSoto Canyon was undertaken along 3 depth transects on the canyon wall, axis, and adjacent slope. Sediment, terrain, and water mass parameters were also compiled for the same stations. Within the canyon, macrofaunal abundance decreased, evenness increased, and richness followed the expected parabolic curve with depth, peaking at 1100 m. Cluster analysis identified 3 canyon depth groups that conformed to established bathymetric boundaries for the non-canyon Gulf of Mexico slope: Group I at <500 m, Group II at 669-1834 m, and Group III at >2000 m. Explanatory environmental models indicate that canyon community structure was strongly correlated with oxygen concentration and fluorescence, with a weaker potential influence from any of salinity, particulate organic carbon, sediment organic carbon, or slope. Comparisons of the habitats indicated that abundances were highest on the canyon wall. Slope community structure differed from that of either of the canyon habitats. Environmental models consisted of single variables including oxygen concentration, sediment organic carbon, slope, and temperature with similar explanatory values. Community differences within the canyon and between the canyon and adjoining slope contradict previous findings of a single faunal zone for the whole study area. Factors that may contribute to inter-habitat heterogeneity include potential hydrocarbon seepage, organically enriched sediment deposits along channels, or remnant influence from the Deepwater Horizon spill, warranting more research into this dynamic ecosystem.

Degradation of aniline in groundwater by persulfate with natural subsurface sediment as the activator

Aniline is reported as a toxic contaminant in the groundwater at some industrial sites. Persulfate oxidation is a promising method to degrade aniline. However, the lack of appropriate activation method limited its application in extensive engineering of groundwater remediation. This paper aims to evaluate the feasibility of aniline degradation in groundwater by persulfate with in-situ subsurface sediment as an activator. Our findings suggested that the Fe(II)-O complex in sediment interacted with persulfate to produce SO4–, OH and Fe(IV) as indicated by the radical scavenging studies. Interestingly, data further revealed that the presence of the sediments simultaneously induced a non-radical mechanism in the degradation process that oxidized aniline to form two aminophenol isomers and azoxybenzene (first detected), which possibly mineralized as indicated by the significant amount of TOC removal in 24 h. The stoichiometric efficiency of the treatment system was substantial in all evaluated conditions. It was notably enhanced by increasing either the initial amount of persulfate, aniline or mass of aquifer sediments. These results confirm that the persulfate without other high-cost activation technologies can be used for in-situ remediation of aniline contaminated groundwater as the sufficient subsurface sediment is an excellent activator and urge the reassessment when employing this technique for remediation purposes since each contaminant may demonstrate a different degradation mechanism.

DEVELOPMENT AND VALIDATION OF EXPRESS PROCEDURE FOR ISOLATION AND QUANTITATIVE DE-TERMINATION OF WATER-SOLUBLE POLYSACCHARIDES FROM HIGH DEVISIL ROOTS

The aim of the study was to develop and validate an express procedure for the isolation and quantification of water-soluble polysaccharides from high devisyl roots (Ínula helenium L.). In order to accelerate the process of extracting biologically active substances from the roots of high devisil, as well as to increase the yield of water-soluble polysaccharides, it was decided to use an ultrasonic bath. By varying the process parameters, it was possible to select optimal extraction conditions of water-soluble polysaccharides of high-grade roots under ultrasound treatment conditions: raw material grinding 0.5–1.0 mm, temperature – 80 °C, extraction multiplicity – 3, extraction duration – 15 min, ultrasound frequency – 35 kHz, ratio of raw material to extractor 1 g per 15 ml. The proposed technique allows to intensify the process of preparing polysaccharides water-soluble from roots high and to reduce the time spent on it up to 4-5 hours, as well as to increase the yield of the product up to 31.6% in terms of absolutely dry raw materials. The developed method is precise under the conditions of repeatability, correct, stable and has a rather strict linear dependence of the sediment mass on the analysed raw material mass at gravimetric determination of polysaccharides water-soluble in the roots of high devisil. The technique can be used for express analysis of high devasil roots quality, as well as for industrial production of water-soluble polysaccharides from this kind of raw material.

Sediment transport by the burrowing activity of snow vole (Chionomys nivalis) in subalpine prairies of the Parâng Mountains (Romania): Quantitative modelling and methodological perspectives

Over the last decades, animal activity has been explored and reported as a potential source of natural hazards, such as the destruction of a beaver dam potentially triggering a flash flood downriver. However, the sediment source or sediment budget related to animal activity has received very little attention from geoscientists to date. The main goal of this study is to quantify the biogenic activity of the European snow vole (Chionomys nivalis) as a sediment source in the subalpine prairies of the Parâng Mountains, Southern Carpathians. Only the direct action of this rodent was analyzed, namely the spatial distribution and frequency of burrowing, quantitative analysis of the mounds, and rate of sediment excavation and mass transfer caused by burrowing and tunnel digging. To do this, 838 burrows and mounds were mapped and measured in eleven plots, and excavated volumes of sediment and mass transfers were calculated following three approaches: 1) measuring the weight of excavated debris; 2) measuring the dimensions of excavated debris; and 3) measuring burrow dimensions. The fieldwork revealed three preferred aspects: south, southeast, and west. The amount of displaced soil was highly variable depending on the approach used, ranging from 3.41 m3/ha to 21.08 m3/ha. As such, snow vole biogenic activity, which is due to the long-term opening of the landscape for traditional transhumance and sheep farming, should be considered to be an important sediment source in the subalpine and alpine prairies of the Parâng Mountain.

Plackett Burman design for microplastics quantification in marine sediments

Microplastics are gaining worldwide attention due to their omnipresence. The marine environment is one of the most affected systems; especially the sediment compartment. Microplastic separation from the sediment matrix is the first step to evaluate its abundance and availability. Nevertheless, a lack of consistency in extraction protocols is a fact. This paper describes the optimization of the microplastic extraction procedure from marine sediments. The Plackett-Burman saturated factorial design was used to identify the significant factors and to select optimum working conditions. With this purpose, the following variables were studied: the number of extractions; the amount of sediment; the settling time; the density separation solution volume; the agitation time and the suitability of using wet or freeze-dried sediment. The Plackett-Burman design has revealed that the most statistically significant variables were sediment mass and agitation time. The optimized method was applied for two marine sediments collected in the Mar Menor Lagoon.

Transport and Deposition Patterns of Particles Laden by Rising Submarine Hydrothermal Plumes

AbstractTransport and deposition behavior of mineral particles driven by hydrothermal plumes along mid‐ocean ridges is one of the least understood processes in geoscience. We reveal the mechanism and three typical transport patterns of particles emitted from submarine vents and subsequently laden by plumes in the stratified deep ocean with or without crossflows, that is, suspension, near‐vent deposition, and long‐distance transport, by developing a Lagrangian model coupled with a computational fluid dynamics model and using in situ measurements as model inputs. The particle trajectories suggest a general expression that predicts a linear variation of deposition location with the reciprocal of settling velocity, which potentially leads to a power law distribution of sediment mass along the radial direction. Our findings provide a new perspective on the accumulation of sediments near hydrothermal vents, indicating a critical role of the entrainment of plumes and consequent vortex systems in controlling deposition flux.

Neogene to recent evolution of the Southern Gulf of Mexico basin: Tectonic controls on deep‐water sediment dispersal systems

AbstractNewly available two‐dimensional (2D) and limited three‐dimensional (3D) reflection seismic data coupled with publicly available well and core data were used to generate the first comprehensive regional basin evolution model for the deep‐water Neogene to recent southern Gulf of Mexico (GoM). This evolution is presented in the context of contemporaneous onshore tectonic drivers and predecessor basin tectonic history. Dynamic uplift to the west in North America, transpression to the south and tectonically influenced salt tectonics to the east served to collapse the margins of the southern Gulf of Mexico Basin throughout the late Neogene and into the modern. This collapse and salt inflation served to shut off efficient sediment transport into the axial deep basin. Newly developed nearshore extensional accommodation along both the western margin of the basin and salt‐rooted orogenic structures to the south and east appear to have baffled coarser‐caliber sediment input from southern (Mexican) sediment sources into the deep Gulf of Mexico Basin beginning in the late Miocene. This sequence is recorded in the southern GoM basin by a transition from large early–mid Miocene submarine channel belts to late Miocene–recent sediment wave fields and mass transport deposits. Improved resolution of new 2D and 3D subsurface seismic reflection data shows that sediment waves of the southern Gulf of Mexico are supercritical bedforms, long wavelength antidunes and cyclic steps, not contourites. These supercritical bedforms are among the most spatially expansive and morphologically largest documented globally. The location and evolution of these bedforms appears closely tied to the tectonically driven history of margin collapse, salt inflation and the starving of the deep basin of coarse‐grained sediment. Cumulatively, the tectonic drivers that intuitively should have increased sediment flux into the deep southern Gulf of Mexico acted to ‘pinch off’ the basin, starving it of sediment supplied from southern sediment sources.

Rock Avalanche-Generated Sediment Mass Flows: Definitions and Hazard

Rock avalanches can trigger destructive associated hazards following the initial collapse and fragmentation of a rock slope failure. One of these associated hazards occurs when the material derived from the initial collapse of the source zone impacts and mobilizes a mass flow composed of sediment from along the travel path. These mass flows can be grouped into radial impact areas that occur on relatively flat, open terrain (typically a floodplain), and more linear impact areas that occur in channelized terrain. Rock avalanche-generated sediment mass flows are an important consideration because they can significantly increase the area impacted by an event, thereby increasing the hazard area, especially in valley bottoms where there are likely more elements at risk. Existing runout prediction methods do not consistently account for the increase in the impact area from rock avalanche-generated sediment mass flows. Thus, there is a need for a simple data-supported method for estimating the extent of mass flow impacts resulting from an initial rock avalanche event with sediments along the potential travel path. This paper presents data from 32 rock avalanches and 23 rock avalanche-generated sediment mass flows from around the world, described using a consistent set of quantitative and qualitative attributes. A wide range of mass flow impacts were observed, with the sediment mass flow impact area or runout length exceeding the impact of the coarse, rocky debris in some cases. The area and length impacted by the coarse, rocky debris is estimated using multiple linear regressions considering the event volume and topographic features. The sediment mass flow dataset is used as input to develop an exponential distribution of the area or runout length of the sediment mass flow over that of the coarse, rocky debris. A decision tree framework is presented for estimating the extent of potential rock avalanches and potential rock avalanche-generated sediment mass flows for hazard and risk analysis, which is demonstrated by comparing the stochastic empirical predictions to those from numerical runout modelling.

Budget and fate of sedimentary trace metals in the Eastern China marginal seas

To achieve a better understanding of global biogeochemical cycle and budget of trace metals (TM) in the world's ocean, a comprehensive study of the level, fate and burial flux of TM in surface sediment from the Eastern China Marginal Seas (ECMS) was conducted. The results indicated that Pb, Zn, Cu, and Cr were highly concentrated in mud deposits and primarily controlled by the natural processes of sediment composition and regional hydrodynamics, whereas As had a close association with Mn and was mainly derived from anthropogenic activity. The sediment mass inventories of Pb, Zn, Cu, Cr, and As in the ECMS (~220,780 km2) were estimated to be 28,324, 92,192, 23,434, 94,560 and 11,968 t/yr, respectively. A mass budget model revealed that riverine runoff, coastal erosion input and atmospheric deposition (dry and wet) constituted 62–76%, 15–37% and 2–9% of the total Pb, Zn and Cr influxes, respectively, while more than 4,690 t of Cu annually outflowed to the open seas to balance the budget. More importantly, we found that the sum of the estimates of these contributions tended to fall short of the calculated depositional fluxes of As, implying that anthropogenic activities probably have altered the natural geochemical cycle of As. Our results suggest that the ECMS constitutes a major final repository of TM at the Asia scale; however, the burial fluxes of trace metals are expected to decrease due to enhanced environmental investments by the Chinese government and decreased suspended particulate TM loads from the Chinese major rivers.

Consolidated sediment budget of Lake Tana, Ethiopia (2012–2016)

Lake sediment budgeting is a vital tool to better understand catchment sediment fluxes. It allows assessing lake lifetime and can be used to design improved catchment management plans. Over the past few years, we collected sediment and runoff discharge data at fine spatial-temporal resolutions for the Lake Tana Basin (LTB), Ethiopia. Based on these data, this study presents a consolidated sediment budget of Lake Tana, following the proof of concept by Lemma et al. (2018). Sediment yield (SY) was quantified for 15 rivers and 2 lake outlets based on 12,671 suspended sediment concentration (SSC) samples, making this the most complete dataset for Lake Tana. In particular, we investigated seasonal and temporal patterns of sediment dynamics and the role of lakeshore floodplains. The latter was done by comparing the SSC measurements at upper and lower borders of the floodplains. Sediment rating curves were prepared that account for land cover conditions and rainfall seasonality. SY calculations for the main contributing rivers take bedload fluxes into account by means of a bedload rating curve. As a result, the gross annual sediment mass mobilized on the hillslopes of LTB was 33.30 Mt (9.93 Mt from ungauged rivers), dominantly from large river catchments in the southern and eastern parts of LTB. SSC and SY are generally larger at the beginning of the rainfed cropping calendar (May–June). By the end of rainfed cropping calendar (September–October), SY decreases. Floodplains store 2.28 Mt suspended sediment whereas annually an average SY of 31.02 Mt entered the lake. From this, 96.6% is suspended load and 3.4% is bedload. With ca. 30 Mt sediment deposited in the lake, its mean trapping efficiency equals 97%. Only 1.14 Mt of sediment leaves the lake through the two outlets. The rate of lake sedimentation (9.8 kg m−2 yr−1) is in line with the sedimentation rates of large lakes in the world. However, because Lake Tana is shallow, its expected lifetime is only 918 years. Moreover, this study is useful for managing freshwater ecosystems that requires understanding of sedimentation rate and associated reduction in storage capacity of lakes, especially lakes that are shallow and have experienced extensive catchment degradation.

Paraglacial adjustment of sediment slopes during and immediately after glacial debuttressing

Daily time lapse imagery and pixel tracking was used to monitor and track spatial and temporal changes in sediment-mantled hillslopes, during and immediately after glacier retreat in the Fox Glacier/Te Moeka o Tuawe valley, New Zealand. Observations from 2014 to 2018 of the Fox Glacier and surrounding hillslopes show hillslope failure is primarily coincident with, and triggered by, glacier retreat with rainfall accelerating movement of the hillslope. During glacier retreat, failure of the hillslope primarily occurred through sediment sliding, internal deformation of the sediment and occasional surficial debris falls, flows and avalanches delivering approximately 9.2 M m3 of sediment directly to the underside of the glacier over the study period with a maximum daily averaged movement of 0.4 m per day of the main sediment mass. Following debuttressing, hillslope failure became dominated by localised rainfall-induced debris flows which initiated gullying of the sediment-mantled slope. Ongoing instability of the slope and associated movement is maintained by toe erosion from the Fox River and melting dead ice, while continued rapid failure is facilitated through localised debris flows. The tracking of temporal and spatial changes of sediment-mantled hillslopes during glacier retreat has shown broad-scale hillslope response to occur quickly within days of rainfall or accelerated glacier retreat, particularly during summer. Debris flows, commonly thought to be a dominant erosion process within paraglacial environments, only occur following complete debuttressing and are supply-limited, only occurring after sediment sliding has occurred. Unlike many other case studies, sediment connectivity immediately following glacier retreat is high due to a lack of storage space and high rainfall inducing mass movements, efficiently delivering hillslope sediments to the proglacial stream channel. Attempts to quantify displaced volumes of sediment from paraglacial systems are likely underestimated due to a) a lack of focus on the early and latter stages of debuttressing b) a reliance on debris flows being a primary transport mechanism, and c) sediment being delivered sub-glacially rather than supra-glacially, further enhancing connectivity.

Assessing Subaquatic Mass Movement Hazards: an Integrated Observational and Hydrodynamic Modelling Approach

High-resolution lake and reservoir bathymetric surveys can pinpoint locations that may experience underwater landslides (subaquatic sedimentary mass movements). These can pose a risk to underwater and shoreline infrastructure. This paper outlines an approach for using spatial variation in sedimentary patterns to identify areas susceptible to subaquatic mass movements in lakes and reservoirs. This study focusses on Lake Biel (Switzerland), which has experienced a protracted history of upstream alteration of river flow. Altered flow patterns increase risk of unstable sedimentary features and subaquatic mass movements. Data from sediment traps and cores, Acoustic Doppler Current Profilers and results from a 3D hydrodynamic model gave a consistent picture of spatial and temporal variation in weather-related sedimentation. Erosion caused by short-term rain events contributes the largest proportion of sediments to the lake. Strong rain events combine with typical wind patterns to drive lake circulation. The net effect results in preferential sedimentation onto a steeply sloping shelf prone to subaquatic slides. The integrated approach outlined here incorporates short- and long-term sediment dynamics to provide a systematic assessment of lake sedimentation and potential mass movement hazards. This research represents a first step in developing a risk-evaluation tool for aquatic hazard evaluation.

Similarities and contrasts between the subaerial and subaqueous deposits of subaerially triggered debris flows: An analogue experimental study

ABSTRACT Debris flows and lahars are dense masses of water and sediment which are common phenomena in mountainous and volcanic regions, respectively. Where these flows debouch into water bodies they can trigger impulse waves (tsunamis) and form subaqueous deposits. Such deposits are important indicators for areas at risk from debris flows, lahars, and tsunamis and form archives of past environmental conditions. Correctly interpreting this archive, however, depends on our understanding of the sedimentology and architecture of the deposits. While subaerial debris-flow deposits have been extensively studied, there is a comparative lack of understanding of the deposits of subaerial debris flows that debouch into a water body. We experimentally investigate the similarities and contrasts between subaerial and subaqueous debris-flow deposits for flows of various magnitudes and compositions initiated in a subaerial environment. We show that flows depositing on a subaqueous plane generally have a deposit area similar to flows forming in a subaerial setting. Deposits forming on a subaqueous plane, however, are typically shorter and wider with similar thickness, as a result of interactions between the flow and the reservoir water body. Both in subaerial and subaqueous environments the deposits form coarse-grained lateral levees and frontal snout margins. However, where the levees are able to laterally confine the subaerial flows leading to deposits with constant to tapering width, the subaqueous deposits widen with distance offshore because of flow fluidization. Moreover, the frontal snout is often very dispersed, a sharp frontal margin is absent, and many isolated particles are deposited in front of the main deposit margin as a result of interactions between the debris flow and the reservoir water body. These results largely agree with observations of subaqueous pyroclastic-flow deposits. The similarity in area of subaerial and subaqueous deposits suggests that we can apply empirical relations based on subaerial flows to estimate the inundation area and flow volume of subaerial–subaqueous flows.

Diversity and composition of benthic asellote Isopoda from two different New Zealand continental margin habitats - implications of habitat heterogeneity, productivity and depth

As part of the New Zealand government Ocean Survey 20/20 programme (OS 20/20, 2006–2013), samples from the Chatham Rise and Challenger Plateau collected in 2007 were analysed to determine the effects of key environmental parameters, in particular sediment and water mass properties, on spatial changes in the community structure (abundance, diversity and community composition) of bathyal asellotan isopods. Benthic collections were obtained in austral autumn (May/June 2007) and included a total of 21 epibenthic sledge samples taken from the upper slope between 218 and 1239 m. Due to the contrasting environmental settings between the Chatham Rise and Challenger Plateau, in terms of surface productivity and habitat heterogeneity, we expected the abundance, regional (or gamma-) diversity and community composition of benthic isopods to significantly differ between the two regions, and furthermore local (or alpha-) diversity and abundance (density) to decrease with increasing depth. Consistent with our assumptions, multivariate PERMANOVA analysis revealed a clear distinction in species composition between the Chatham Rise and Challenger Plateau with satellite surface chlorophyll (Chl) a and bottom temperature being the main environmental drivers. In contrast to previous benthic studies from the same sampling campaign, however, differences in isopod density and diversity between the two regions were not significant, either at species, or generic and family level. In addition, no depth-related changes in abundance and diversity could be observed at any hierarchical level. Instead, isopod densities at species and generic level were positively correlated with satellite surface Chl a and %silt, whilst species and generic diversity could be positively linked to the amount of total organic matter (TOM) in surficial sediments. In total, 97 asellote species in 54 genera and 15 families could be identified from both regions, of which 90.7% were likely new species. Species diversity was average to high when compared to other regions in the Northern and Southern hemispheres. However, neither for Chatham Rise nor for the Challenger Plateau did the species accumulation curves reach an asymptote, indicating that additional samples are required to provide more robust diversity estimates.

Vibration Data Processing for Bedload Monitoring in Underwater Environments

This paper proposes a novel data processing framework dedicated to bedload monitoring in underwater environments. After calibration, by integration the of total energy in the nominal bandwidth, the proposed experimental set-up is able to accurately measure the mass of individual sediments hitting the steel plate. This requires a priori knowledge of the vibration transients in order to match a predefined dictionary. Based on unsupervised hierarchical agglomeration of complex vibration spectra, the proposed algorithms allow accurate localization of the transients corresponding to the shocks created by sediment impacts on a steel plate.

Integrated Morpho-Bathymetric, Seismic-Stratigraphic, and Sedimentological Data on the Dohrn Canyon (Naples Bay, Southern Tyrrhenian Sea): Relationships with Volcanism and Tectonics

Submarine canyons are geomorphologic lineaments engraving the slope/outer shelf of continental margins. These features are often associated with significant geologic hazard when they develop close to densely populated coastal zones. The seafloor of Naples Bay is deeply cut by two incisions characterized by a dense network of gullies, namely the Dohrn and Magnaghi canyons, which develop from the shelf break of the Campania margin, down to the peripheral rise of the Eastern Tyrrhenian bathyal plain. Seismic-stratigraphic interpretation of multichannel seismic reflection profiles has shown that quaternary tectonics and recent to active volcanism have exerted a significant control on the morphological evolution and source-to sink depositional processes of the Dohrn and Magnaghi submarine canyons. The Dohrn canyon is characterized by relatively steep walls hundreds of meters high, which incise a Middle-Late Pleistocene prograding wedge, formed by clastic and volcaniclastic deposits associated with the paleo-Sarno river system during the Mid-Late Pleistocene. The formation of the Dohrn canyon predates the onset of the volcanic eruption of the Neapolitan Yellow Tuff (NYT), an ignimbrite deposit of ca. 15 ka that represents the bedrock on which the town of Napoli is built. Integrated stratigraphic analysis of high-resolution seismic profiles and marine gravity core data (C74_12) collected along the flanks of the eastern bifurcation of the head of Dohrn Canyon suggests that depositional processes along the canyon flanks are dominated by gravity flows (e.g., fine-grained turbidites, debris flows) and sediment mass transport associated with slope instability and failure.

Development of a non-coupled algorithm for simulating long-term sedimentation in the Zonouz dam reservoir, Iran

This paper reports the development of a non-coupled algorithm and its application in a real case study. The main objective was to provide 2D/3D, long-term simulation of dam reservoir sedimentation by removing the part of calculations which did not significantly affect the results. The model was used to simulate sedimentation in the Zonouz dam reservoir, Iran, over a 30-year period. The non-coupled algorithm couples the flow, sediment transport, and bed modules, solving the depth-averaged Navier-Stokes equations for the flow module, the 3D equation of sediment mass conservation for the sediment module, and the Exner equation to calculate the bed deformations. This algorithm minimizes the computational costs by optimizing the frequency of interactions between the modules, based on the validity of the quasi-steady-state approximation for the flow and sediment modules. The algorithm is developed using the continuity correction to account for the impacts of time and space lags, and adjust the flow parameters after small changes in the bed level. Due to the highly varying water surface elevations and sloping bed in the reservoir, flooding and drying phenomena may occur. Therefore, some artificial resistance was introduced. The Zonouz dam, located on the Zonouzchay River, supplies water to 950 ha of agricultural land, and has other environmental purposes. The predominant sediment type was suspended sediment. The reservoir surface was discretized by a 91 × 80 grid. The number of layers in the z-direction was eight, with different thicknesses. The reservoir was hydrographically surveyed in 2012 and 2016, and the numerical results were verified accordingly. The “quasi-steady time step” and the “updating time step” were equal to 1 day and 8 h, respectively. For flood days, a 3-h updating time step was used. The criterion for determining the steady-state condition was 2%. The simulation indicated that the sediment deposition in the reservoir area was mostly accumulated at the inlet of the reservoir. The predicted value of the total cumulative volume of the deposited sediment in 2042 was approximately about 1.0 Mm3. The present study demonstrated the appreciable accuracy and efficiency of the non-coupled algorithm. This algorithm shortened the simulation time and proved that the 3D sediment model is applicable in long-term modeling.

A Mixed Length Scale Model for Migrating Fluvial Bedforms

AbstractWith the expansion of hydropower, in‐stream converters, flood‐protection infrastructures, and growing concerns on deltas fragile ecosystems, there is a pressing need to evaluate and monitor bedform sediment mass flux. It is critical to estimate real‐time bedform size and migration velocity and provide a theoretical framework to convert easily accessible time histories of bed elevations into spatially evolving patterns. We collected spatiotemporally resolved bathymetries from laboratory flumes and the Colorado River in statistically steady, homogeneous, subcritical flow conditions. Wave number and frequency spectra of bed elevations show compelling evidence of scale‐dependent velocity for the hierarchy of migrating bedforms observed in the laboratory and field. New scaling laws were applied to describe the full range of migration velocities as function of two dimensionless groups based on the bed shear velocity, sediment diameter, and water depth. Further simplification resulted in a mixed length scale model estimating scale‐dependent migration velocities, without requiring bedform classification or identification.

Field‐Based Estimate of the Sediment Deficit in Coastal Louisiana

AbstractCoastal and deltaic sediment balances are crucial for a region's sustainability. However, such balances remain difficult to quantify accurately, particularly for large regions. We calculate organic and mineral sediment mass and volume balances using field measurements from 273 Coastwide Reference Monitoring System sites across the Louisiana Coast between 2006 and 2015. The rapid relative sea level rise rate (average 13.4 mm/year) is offset by the small dry bulk densities observed (average 0.3 g/cm3) to produce a 16.2 ± 41.1% mass deficit and 24.1 ± 14.0% volume deficit, significantly smaller than recent predictions for 2000–2100 (73–79% mass deficit). Geostatisical estimates show that this deficit is primarily located in areas not directly nourished by major rivers, yet these regions still accumulate ~24 MT/year of mineral sediment. A fluvial sediment discharge of 113.8 MT/year suggests a coast‐wide trapping efficiency of 31.5 ± 15.8% of the riverine sediment, excluding subaqueous deposition. Organic accumulation accounts for 25% of all mass accumulation during our study period, and total organic mass accumulation per unit area is relatively constant in both directly and indirectly nourished regions. Sediment characteristics in the modern coastal wetlands differ from the Holocene deposit, suggesting secular changes within the system that will likely continue to influence coastal dynamics over the coming decades. Our results suggest that the gap between accommodation and accumulation (mass or volume) during this decade was not as large as the previously predicted century average.