Analysis on Suspended Sediment Deposition Rate for Muddy Coast of Reclaimed Land

A new expression for calculating suspended fine-sediment deposition rate is developed based on theoretic analysis and experiments. The resulting equation is applied to simulation of fine sediment deposition in the reclaimed land in the Hangzhou Bay, China. The hydrodynamic environment in this area is solved by use of a long wave model, which gives the 2D-velocity field and considers bathymetric changes due to fine sediment deposition. The expression is proved convenient to use in engineering practice, and the predicted deposition rate agrees with the annual data available from field measurements from the first year to the third year after the construction of the long groin as a reclaiming method.

Influencing factors of sediment deposition and their spatial variability in riparian zone of the Three Gorges Reservoir,China

Many factors can affect the sediment deposition and soil erosion process in riparian zone, including terrain, sediment transport and water level fluctuations. Clarifying the factors influencing sediment deposition process in the riparian zone of the Three Gorges Reservoirs is an important problem to determine the key area of sediment deposition and its trend of development in the study area. In order to reveal the influence of these environmental factors on the sediment deposition in riparian zone of the Three Gorges Reservoir, this study investigated 1） the amount of deposited sediment in different environmental conditions, 2） the potential factors affecting sediment deposition in riparian zone of the Three Gorges Reservoir, 3） the relationship between the deposited sediment amount and these factors previously mentioned using correlation analysis, and 4） the influence of human activities considered as an additional factor. This study found that 1） slope gradient, elevation, inundating duration and human activities were the main factors influencing sedimentation in riparian zone of the Three Gorges Reservoir, and 2） the impact of each factor varied with spaces. Specifically, in the upper reach from Jiangjin to Fuling, human activities such as gravel dredging, bank revetment and ports and wharfs constructing disturbed considerable amounts of deposited sediment, as a result, there was no natural law to dictate the distribution. In the middle reach from Fuling to Fengjie, slope gradient and inundating duration were the controlling factors, and the sediment deposition amount was greater in the areas with a gentler slope or lower elevation. Water flow on gentler slopes generally had lower velocity, resulting in more sediment to deposit. Sites with lower elevations would be drowned by sediment-laden flow with a longer duration resulting from hydrologic regime controlled by the operating strategy of the Three Gorges Reservoir, leading to a larger amount of sediment deposition. In the lower reach from Fengjie to Zigni, slope gradient was similar to the middle reach, performing a primary factor, while other factors showed little relationship with sediment amount.

Distribution,fractionation,and contamination assessment of heavy metals in offshore surface sediments from western Xiamen Bay,China

Surface sediment samples were collected at 21 offshore sites in western Xiamen Bay, Southeast China. Total concentrations of Li, V, Cr, Co, Ni, Cu, Zn, St, Mn, Pb, Ba, Fe, and Ti were determined by inductively coupled plasma-optical emission spectrometry; Hg was determined by atomic fluorescence spectrometry. A modified BCR sequential extraction procedure was used to extract fractions of the above elements. Concentrations of Pb, Cr, and Hg at most sites met the primary standard criteria of Marine Sediment Quality except site S12 for Pb and S7 for Cr, while concentrations of Zn at 17 sites and Cu at seven sites exceeded the criteria. The mean concentration of Hg was three times higher than the background, with a possible source being the Jiulong River. Fe, Ti, Ba, Co, V, and Li dominated the residual phase, mainly from terrestrial input. Ni, Cr, Pb, and Hg in the non-residual phase varied largely between sites. Sr, Mn, Cu, and Zn were mainly in the non- residual fraction. Most sites showed considerable ecological risk; exceptions were site S7 （very high） and sites S10, S11, and S14 （moderate）. Cu showed moderate-to-high pollution and Pb exhibited no-to-low pollution, while other metals had a non-pollution status according to their ratios of secondary phase to primary phase （RSP）. Results of two assessment methods showed moderate pollution and a very high ecological risk for Cu, Zn, Ni, and Cr at site S7, which might be due to the local sewage treatment plant.

Numerical simulation of sediment deposition thickness at Beidaihe International Yacht Club

The finite element method （FEM） was used to simulate sediment hydrodynamics at the Beidaihe International Yacht Club, and a two-dimensional model was established. The sediment movement and deposition were analyzed under many tidal conditions in conjunction with the hydrological regime of the Daihe River. The peak value of the sediment deposition thickness appears in the main channel and around the estuary. The sediment deposition thickness is essentially constant and relatively small in the project area. The sediment deposition thickness in the main channel, in the yachting area, and around the hotel is greater than the other areas in the project. Regular excavation and dredging of the channel is the best measure for mitigating the sedimentation.

Distributions of surficial sediments and its response to dynamic actions in the Xiamen Bay sea area, China

Sediment distribution is important for morphodynamic evolution and shoreline changes in coastal zones and estuaries. In the study, the data of 230 surface sediment samples collected from the Xiamen Bay sea area in September 2008 are used to investigate the spatial distribution and sediment transport pathway. The grain size distribution of surficial sediments in the Xiamen Bay area is shown distinctly in this study. In addition, the Grain Size Transport Analysis model is used for conveying trend analysis of the sediment in this area, particularly for determining the sediment movement trend. The results indicate that eight sediment types are present for samples, with clayey silt comprising the highest percentage in the study area at 65.22%. Moreover, in the different subareas, the characteristics of grain size parameters are obviously different owing to different sediment sources and hydrodynamic conditions. Furthermore, runoff, tides, and waves are the main forces dominating sediment dynamics on the seabed and tidal flats, and the sediment movement trend is closely related to hydrodynamic conditions.

The analysis on reservoir sediment deposition and downstream river channel scouring after impoundment and operation of TGP

According to the measured data after impoundment and operation of the Three Gorges Reservoir,the reservoir sediment deposition and downstream river channel scouring are described briefly and compared with the research results achieved in the demonstration stage.It is indicated through analysis that the reservoir sediment deposition and downstream river channel scouring during 8-year impoundment and operation are still within the original forecast,so the original forecasting results are feasible.The further observation and comparison should be conducted because the comparison between the observed data and the original forecast is not so sufficient in time and the prototype observation and related research work should be strengthened in the future.

KINETICS OF LEAD ADSORPTION BY XIAMEN BAY SEDIMENTS

The kinetics of Pb adsorption in seawater by surface sediments from Xiamen Bay was simulated and the effects of seawater conditions were studied . When water temperature changed from 20 to 30℃, pH from 5 to 8 and salinity from 30 to 4 . the adsorption rate increased by about 50% , one order of magnitude and 5 times, respectively . A negative exponential relation between the adsorption rate and salinity has been found . The adsorption processes can be simulated by the exchange- equilibrium kinetic model . Adsorption rate constant, apparent activation energy and equilibrium adsorptive capacity have been quantitatively determined . The adsorption of Pb by sediments is essentially a chemical action .

THE VERTICAL DISTRIBUTIONS AND SOURCES OF PAHs IN SEDIMENT OF XIAMEN BAY

This study on the vertical distributions and sources of sixteen PAHs in Xiamen Bay after their separation and determination in sediment cores from No.1 and No.5 Stations, showed that PAHs concentrations varied from 158 to 337 ng/g dry weight, and that ΣPAHs varied from 1.1 to 6.0 μg/g. The vertical concentration distributions at No.1 Station varied slightly (average of 16 PAHs, 242 ng/g; ΣPAHs 1.9 μg/g), except for a maximum at the depth of 3-6 cm (317 ng/g and 2.9 μg/g). The vertical concentration distribution at No.5 Station changed irregularly, and there was also a maximum at the depth of 30-33cm (337 ng/g, 6.0 μg/g). No.5 Station (in the inner bay) was much more contaminated by PAHs than No.1 Station (in the inlet of the bay). The concentrations of PAHs in Xiamen Bay were much lower than the average in the coasts of the world. The sources of PAHs in Xiamen Bay were mainly urban discharge, industry and combustion of fuels.

MECHANISM OF PHOSPHORUS RELEASE FROM THE SEDIMENT-WATER INTERFACE IN XIAMEN BAY

The adsorption/desorption of phosphorus across the sediment -water interface is the main mechanism that controls the buffering capacity of DRP in coastal and estuarine water. Determination by three processes revealed that: 1) DRP flux from early diagenesis in surface sediment is F = 31.9ug/(m2.d ), which is only 1/1600 of the ammonia released; 2) at normal temperature and in the long term, the TDP released by adsorption /desorption across the sediment-water interface is a function of the major environmental factors; and 3) based on the determined SODR and assumed average water depth H(m) and residence time tR(d), the maximum flux of DRP can be estimated.

Effects of an oasis protective system on aeolian sediment deposition:a case study from Gelintan oasis,southeastern edge of the Tengger Desert,China

Desert-oasis ecotones are boundary areas between oases and desert ecosystems.Large efforts to control sediment and stabilize these boundaries depend on understanding sedimentary processes,especially aeolian transport and deposition.Previous studies on aeolian sediment deposition have focused primarily on a single land surface type or a single engineering approach.Few studies have considered deposition in a multi-layer oasis protective system.A complete oasis protective system consists of an outer bare sand area,a sand barrier zone,a shrub and herbaceous plant zone,and a farmland shelter zone.This study used sedimentary analysis to quantify grain-size characteristics in samples from the four land surfaces under different types of weather conditions in the Gelintan oasis of the Tengger Desert,the fourth largest desert in China.The results showed that aeolian sediment deposition decreased from the outer bare sand area through the oasis protective system and into the interior.The four land surface types showed significant differences in deposition volume(P<0.05).Deposited sediment showed gradual decrease in dominant grain-size from sand to silt,but sediment deposited during dust weather contained a larger coarse-grained fraction.From the outer desert to the inner oasis,transport mechanisms shifted from saltation(sand)to suspension(silt and smaller)in non-dust weather.During dust weather,deposition primarily occurs from near-surface aeolian sand transport with saltation.Sediment sorting decreased from exterior to interior zones of the protective system while skewness and kurtosis showed no significant change(P<0.05).These results can help inform strategies for stabilizing and protecting desert-oasis ecotones in this region and other localities.

Experimental Analysis of Sediment Deposition Due to the Effect of an Upstream Reservoir Backwater

The phenomenon of aggradation due to sediment accumulation upstream reservoirs had been studied in this research. For this purpose, groups of experiments were conducted in a laboratory with 25 m long, 0.80 m wide and 0.70 m deep channel. A block was built at the end of the channel to work as a dam to impound water. The channel was supplied with drainage pipes on both sides to release water out in a manner similar to what happens in reservoirs. The bed of the channel was filled with sand of 0.80 mm median sieve diameter and 0.72 geometric standard deviation. The slope was 0.0093 for all experiments. Two sizes of sand were used representing the sediment. The median diameter and geometric standard deviation of the first were 0.365 mm and 0.46 mm, respectively. The second sample had 0.65 mm median diameter and 0.67 standard deviation. A total of 70 experiments were conducted in two groups to examine effects of sediment transport rate, particle size of sediment and flow velocity on aggradation characteristics. The results showed that there was a strong linear direct relationship between aggradation elements （length and depth） with the rate of sediment transport. Groups of dimensionless parameters affecting the aggradation characteristics were used to develop empirical equations to predict the length, maximum depth of aggradation and predict transient bed profile. The results of empirical approach were compared with the measurement data and previous numerical method. The results indicated that the percentage error was 19% to 31% for length of aggradation and -21% to 26% for maximum depth of aggradation. The results also showed that the sediment materials were deposited closer to the body of the dam when the released water from the dam is higher than the inflow.

Sediment Deposition and Resuspension in Mouth Bar Area of the Yangtze Estuary

A comprehensive analysis is conducted based on observations on topography, tidal current, salinity, suspended sediment and bed load during the years of 1982, 1983, 1988, 1989. 1996, and 1997 in the Yangtze Estuary. Results show that the deformation of tidal waves is distinct and the sand carrying capacity is large within the mouth bar due to strong tidal currents and large volume of incoming water and sediments. Owing to both temporal and spatial variation of tidal current, deposition and erosion ore extremely active. In general a change of up to 0.1 m of bottom sediments takes place during a tidal period. The maximum siltation and erosion are around 0.2 m in a spring to neap tides cycle. The riverbed is silted during flood when there is heavy sediment load, eroded during dry season when sediment lo:ld is low. The annual average depth of erosion anti siltation on the riverbed is around 0.6 m. In particular cases, it may increase to 1.4 m to 2.4 m at some locations.

Storm Liquefaction Deposits:A Possibility of Time Reversal in Sedimentary Strata of an Estuarial Coastal Area

In the sedimentary strata dating of estuarial coastal areas,it is often found that there is phenomenon of time-reversal in strata.The seabed sediments could be liquefied under storm waves.A laboratory wave flume experiment demonstrated that storm-induced liquefaction deposits are formed by the oscillations of liquefied sediments.In this paper,the particle size distribution and ^(210)Pb_(ex) specific activity of the sediment samples from the liquefaction disturbed zone and adjacent stable zone of the Yellow River Delta were tested.The stratigraphic divisions based on storm liquefaction deposit sequence can effectively explain the vertical changes in particle size and ^(210)Pb_(ex) specific activity.Due to the differentiation of particles during the storm induced liquefaction,coarse and fine particles regrouped,which could explain the phenomenon of time-reversal in dating data.

Local hydraulic jump effects on sediment deposition in open-channel flume experiments

When a river channel is narrow,bifurcated,or intersected,or when extreme weather or geological disasters cause shed rock masses to occupy a river flood channel,local hydraulic jumps may develop in the channel.Natural disasters such as landslides,floods,and debris flows occur upstream,will result in large transport rate of large-sized gravel particles.Those particles may be blocked in hydraulic jump areas,causing river channel water depth to rise.In this study,the effect of local hydraulic jumps on the sediment deposition rate was investigated in flume experiments.The ratio of upstream and downstream Froude numbers,particle size,Sediment supply intensity,and flow discharge all affected the sediment deposition rate.With increases in the ratio of upstream and downstream Froude numbers,particle size,and sediment supply intensity,the sediment deposition rate increased.The sediment deposition rate decreased with an increase in flow discharge.Approach hydraulic conditions and particle properties jointly determined the sediment deposition rate in a hydraulic jump section,and an empirical formula was developed using those parameters to calculate the sediment deposition rate.Thus,to identify risks and prevent disasters in mountain rivers,local changes in hydraulic conditions and particle properties need to be jointly evaluated.

Sediment yield and erosion–deposition distribution characteristics in ephemeral gullies in black soil areas under geocell protection

Investigating the effect of geocells on the erosion and deposition distribution of ephemeral gullies in the black soil area of Northeast China can provide a scientific basis for the allocation of soil and water conservation measures in ephemeral gullies.In this study,an artificial simulated confluence test and stereoscopic photogrammetry were used to analyze the distribution characteristics of erosion and deposition in ephemeral gullies protected by geocells and the effect of different confluence flows on the erosion process of ephemeral gullies.Results showed that when the confluence flow was larger,the effect of geocell was more evident,and the protection against ephemeral gully erosion was stronger.When the confluence flow rates were 0.6,1.8,2.4,and 3.0 m^(3)/h,ephemeral gully erosion decreased by 37.84%,26.09%,21.40%,and 35.45%.When the confluence flow rates were 2.4 and 3.0 m^(3)/h,the average sediment yield rate of the ephemeral gully was close to 2.14 kg/(m^(2)•min),and the protective effect of ephemeral gully erosion was enhanced.When the flow rate was higher,the surface fracture of the ephemeral gully was more serious.With an increase in confluence flow rate,the ratio of erosion to deposition increased gradually,the erosion area of ephemeral gullies was expanded,and erosion depth changed minimally.In conclusion,geocell measures changed erosion patterns by altering the rill erosion/deposition ratio,converting erosion from rill erosion to sheet erosion.

Exploration of the Mechanisms for the Low Sensitivity of Deposition Flux to Upstream Sediment Reduction in the North Passage, Yangtze Estuary

Deltas are densely populated industrialized regions,and home to important ports and navigation channels.Due to human interferences,the Yangtze Estuary has experienced a significant reduction in sediment load caused by the Three Gorges Dam(TGD),as well as adjustment to local morphodynamics by the Deep-water Navigation Channel(DNC).While the dramatic reduction in sediment triggers the increased channel erosion,the deposition flux of the DNC located at the estuary mouth has little change.To explore the physical mechanism of this phenomenon,a two-dimensional model is used to establish the relationship between sediment load and the sediment budget of channels based on the bathymetry in 2016.Model results show that the tidal reach and the inner estuary have a negative sediment budget.And the seasonal characteristics of water and sediment fluxes become less obvious downstream.Sensitivity analysis shows that the influence of upstream sediment load on deposition flux decreases along the channel,with a transition from deposition to erosion occurring in the tidal reach.For the last-level bifurcation,the annual siltation of sediment in the North Passage(NP)decreases by 4.5%with low sensitivity.This is attributed to the reduction of sediment load partially mitigated by riverbed erosion and cascade bifurcations.In addition,the lateral sediment supply,which accounts for 68%of the sediment input in the NP,is stable.Overall,this study strengthens the understanding of the relationship between sediment load and artificially deepened systems,thus allowing for better management of estuarine sediment and navigation channel.

Effects of soil crust on the collapsing erosion of colluvial deposits with granite residual soil

Collapsing erosion is a unique phenomenon commonly observed on the granite residue hillslopes in the tropical and subtropical regions of southern China,characterized by its abrupt occurrence and significant erosion volumes.However,the impacts of soil crust conditions on the erosion of colluvial deposits with granite residual soils have only been studied to a limited extent.To address this issue,this study investigates the impacts of three soil crust conditions(i.e.,without crust,10-minute crust,and 20-minute crust)on gully morphology,rainfall infiltration,and runoff and sediment yield during slope erosion of colluvial deposits with granite residues(classified as Acrisols)in Yudu County,Ganzhou City,Jiangxi Province,China,using simulated rainfall tests and photographic methods.The results showed that as the strength of the soil crust increased,the capacity of moisture infiltration and the width and depth of the gully as well as the sediment concentration and yield ratio decreased;at the same time,the runoff ratio increased.The sediment yield in the without-crust test was found to be 1.24 and 1.43 times higher than that observed in the 10-minute crust and 20-minute crust tests,respectively.These results indicate that soil crusts can effectively prevent slope erosion and moisture infiltration,while providing valuable insights for the management of soil erosion in natural environments.

Chemical Determination of Base Status Metals in Soil Sediments and Particulate Matter in Wellington Industrial Estate Location

This research study explored the levels of base status metals in soil sediments and particulate matter in the wellington industrial estate location;the main objectives were to: 1) determine sodium and potassium, 2) determine calcium and magnesium, 3) determine available iron. The following hypotheses were put forward;H0a: there is no significant difference in the concentration levels between Ca and Mg in the study area, H1a: there is significant difference in the concentration levels between Ca and Mg in the study area, H0b: there is no significant difference in the concentration levels between Na and K in the study area, H1b: there is significant difference in the concentration levels between Na and K in the study area. Six locations were used to collect samples with the aid of scoop and gravel free auger (at varying depths of 0 - 5 cm and 5 - 10 cm) which are Wellington Industrial Estate Area 1 (WIEL 1), (WIEL 2), (WIEL 3), (WIEL 4), (WIEL 5), (WIEL 6);the samples were given laboratory treatment. Flame photometer, EDTA, and Spectrophotometer were used in the determinations of sodium and potassium, calcium and magnesium, and available iron respectively. The results indicated that levels of potassium were in medium range (moderately high);sodium levels were generally low when compared to Brook’s classification table. Levels of calcium were generally low and those of magnesium were moderate based on Brook’s table of classification. Levels of available iron which fall within the range of Quijano-Guerta (2003) were high;this implies such levels can lead to toxicity. In all locations, there was decrease in the levels of each metal in the samples with (5 - 10 cm) depth.

Application of a ^(137)Cs fingerprinting technique for interpreting responses of sediment deposition of a karst depression to deforestation in the Guizhou Plateau,China

Deforestation to reclaim land often triggers severe soil erosion in the Guizhou Karst Plateau. 137Cs dating of the deposited sediments in the karst depression bottom was used to estimate soil losses by surface erosion since deforestation started in 1979 on hillslopes in the Shirenzhai catchment, Puding County, Guizhou Province. The catchment has a drainage area of 0.054 km2. The average 137Cs contents of the top and peak layers in five cores of the depression bottom (with an area of 2652 m2), collected in 2009, were 2.35 and 7.25 Bq kg-1, respectively. The medium depths in the depression (which ranged between 84 cm and 113.5 cm with a mean value of 92.1 cm) showed the presence of sediments deposited in 1979. The total volume and weight of the deposited sediments since 1979 were estimated to be 1965 m3 and 2496 t, respectively. The depression bottom can be treated as a temporary impoundment and its sediment trapping efficiency was estimated to be 0.7. The relevant average soil erosion rate on the hillslopes was 2315 t km-2 yr-1 since 1979. The mean 137Cs inventory of the five cores was 7693 Bq m-2, which was ~10 times the local reference inventory of 782 Bq m-2. The total 137Cs activity of the sediments in the bottom was 20.4×106 Bq, and the relevant 137Cs inventory loss from the hillslopes was 358 Bq m-2 (since 1954), which accounted for 45.8% of the reference inventory. As soil erosion was not severe before and after the period of deforestation and following cultivation in 1979-1990, the erosion rates on the hillslopes could potentially reach 7000 t km-2 yr-1.

Quantification,morphology and source of humic acid,kerogen and black carbon in offshore marine sediments from Xiamen Gulf,China

Three types of macromolecular organic matters （MOMs）, i.e. humic acid （HA）, kerogen＋black carbon （KB）, and black carbon （BC） were extracted from marine sediments of Xiamen Gulf, southeast of China. The chemical composition, morphological property and source of the three extractions were characterized by elemental analyzer/isotope ratio mass spectrometry （EA/IRMS） and scanning electron microscope （SEM）. The results showed that KB was the predominant fraction in MOMs, which accounted for 61.79%-89.15% of the total organic content （TOC）, while HA consisted less than 5%. The relative high contents of kerogen and BC, and low contents of HA in the samples indicated that anthropogenic input might be the major source of organic matter in marine sediments near the industrial regions. The characterization of SEM, not only revealed morphological properties of the three fractions, but also allowed a better understanding of the source of MOMs. The δ 13 C values of the three fractions suggested that materials from terrestrial C 3 plants were predominant. Furthermore, the anthropogenic activities, such as the discharge of sewage, coal and biomass combustion from industry nearby and agricultural practices within drainage basin of the Jiulong River, were remarkably contributed to the variations in δ 13 C values of MOMs in the offshore marine sediments.