Estimation of suspended sediment flux from acoustic Doppler current profiling along the Jinhae Bay entrance

A Nortek acoustic Doppler current profiler (NDP) was installed on a moving vessel to survey the entrance to the Jinhae Bay on August 22~23, 2001. The current velocity and acoustic backscattering signal were collected along two cross-sections; water samples were also collected during the measurement. The acoustic signals were normalized to compensate for the loss incurred by acoustic beam spreading in the seawater. The in situ calibration shows that a significant relationship is present between suspended sediment concentrations (SSC) and normalized acoustic signals. Two acoustic parameters have been determined to construct an acoustic-concentration model. Using this derived model, the SSC patterns along the surveyed cross-sections were obtained by the conversion of acoustic data. Using the current velocity and SSC data, the flux of suspended sediment was estimated. It indicates that the sediment transport into the bay through the entrance has an order of magnitude of 100 t per tidal cycle.

Calculating the sediment flux of the small coastal watersheds:a modification of global equations

Two kinds of regression equations are used to reproduce the sediment flux of the 26 small coastal watersheds in southeastern China.The first kind is the global equations suggested by Milliman and Syvitski(1992),Mulder and Syvitski(1996),Syvitski et al.(2003),and Syvitski and Milliman(2007).The second kind is the modified equations revised by the characteristics of the coastal watersheds,including the drainage area,mean water discharge,and mean sediment discharge.Compared with the observations of the hydrometric stations,the global equations overestimate the sediment flux by 1–2 orders of magnitude.By using the modified equations,the accuracy of the estimated sediment flux is significantly improved,with the relative error in the range of 7%–24%.The reason for the overestimation mainly caused by different parameters’domain and regression coefficients between global rivers and study coastal watersheds.This study demonstrates that modification needs to be considered when using global regression equations to reproduce the sediment flux of the small coastal watersheds in southeastern China.

Predicting sediment flux from continental shelf islands,southeastern China

Continental shelf islands are contributors of terrestrial sediment supply to shelf regions,and the sediment flux from these islands shall be quantified.We calculated the sediment flux of continental shelf islands in the southeastern China using two empirical equations under two preconditions.The first,the sediment load/yield of the islands has the same pattern as the adjacent small,mountainous rivers along the coastline;and the second,each of the islands was treated as a single catchment.The results show that the sediment supply from these islands reached an order of magnitude of 1 Mt/a,which is comparable to the supply from the local smaller rivers.A sensitivity analysis indicates that this value represents the lower limit of estimate;if the accurate amount of sub-catchments of any island is considered,then this value will be enhanced slightly.This study demonstrates that the sediment supply from continental shelf islands to oceans is an important factor affecting the regional sedimentation and,therefore,should be paid with attention.

Water Flow and Sediment Flux Forecast in the ChókwèIrrigation Scheme, Mozambique

This study sought to forecast water flow and sediment flux in the scheme as potential contributions for improved management in the Chókwè Irrigation Scheme (CIS). Fieldwork data was collected during dry (DS) and wet (WS) seasons. Flow measurement was performed at 9 stations using a calibrated flow meter OTT C31. Water flow and sediment flux from 2004 to 2019 were used. Hydrodynamic forecast simulations were performed using Mann-Kendall test and ARIMA model for determination of temporal trends. Findings suggest higher values during DS for water discharge and sediment flux. Mann-Kendall test for sediment discharge trends was not significant at 95% significance level, except for the Offtake in WS. ARIMA test for the sediment discharges, at the Intake, for DS and WS, sediments were well described by the ARIMA model and gave a good result for the sediments. Good fit between the observed and the predicted ARIMA model was found. ARIMA model for sediment discharge at CIS based on AIC has a good fit for AR (p = 1), whereby, at the Intake the ARIMA p-value was 0.822 and 0.932, for WS and DS, respectively. Whilst in the Offtake, the ARIMA p-value was 0.877 and 0.893, respectively. These results can be used to improve the CIS management, both for water flow and sediment flux.

Sediment flux and source in northern Yellow Sea by ^(210)Pb technique

Sedimentation of fine-grained deposits on coastal zones and continental shelves are im- portant because of the association with chemical pollutants, and the implication to the impact on biologi- cal processes, the stratigraphic correlations, and changes in sedimentary environments. The Yellow Sea continental shelf receives large quantities of sediment from the Huanghe (Yellow) River. Unfortunately, little attention has been yet paid to the sedimentation on the shallow shelf and its features, and the vertical sediment flux in the area is poorly understood. In this study, nine cores were collected in northern Yellow Sea by the R/V Science 1 in September, 1998 and 1999 to examine the sedimentation rate, sediment flux and the provenance with 210Pb analysis. The 210Pb activity profiles showed that the vertical sediment flux ranged from 0.06 to 1.18 g/cm2·a in the region. In central part of the area, there was a patch of fine-grained mud, with the flux below 0.33 g/cm2·a. Most profiles were featured in two-segment model. Differences in the profiles reflected spatial and temporal variations in hydrodynamic and sedimentary processes. In order to determine the provenance and sedimentary setting in the area, the geochemistry of Ca, Fe, Sr, Cu, Ti and Rb in 11 surficial sediment samples were studied, which showed that in the central northern Yellow Sea, the mud deposit was from multi-source but mainly from the Huanghe River.

Anthropogenic Impacts on the Sediment Flux in the Dry-hot Valleys of Southwest China—an Example of the Longchuan River

The sediment flux data, measured from a dry-hot valley of the Longchuan River, a tributary of the lower Jinsha River, were analyzed with Mann-Kendall test, Seasonal Mann-Kendall test and Sen’s test. In both the upper reaches (Xiaohekou) and the lower reaches (Xiaohuangguayuan), the sediment fluxes showed a significant increase from 1970 to 2001, despite the fact that the water discharge did not change significantly during the period and numerous reservoir constructions which contribute to the trap of sediment. This can be attributed to the intensification of human activities, especially the activities related to land surface disturbances such as deforestation and afforestation, expansion of agriculture land, and road constructions. This increase is more significant in the lower reaches of the river observed at the place of Xiaohuangguayuan due to the dry-hot climate. The profound increase in sediment flux has significant implications for effective management of the sedimentation problems of the on-going Three Gorges Reservoir.

Cross-shore suspended sediment flux in the salt marsh pioneer zone of Chongming eastern beach in the Chang- jiang Estuary in China

Between April 2002 and April 2003,in situ measurements of water depth,current velocity and suspended sediment content were carried out in edge region of East Chongming salt marsh and neighboring bald flat in the Changjiang （Yangtze） Estuary under different weather conditions.Cross-shore suspended sediment flux was calculated and analyzed.The results show that under calm weather conditions,the current velocity process in bald field and salt marsh area varied differently during semidiurnal tidal cycles.Owing to current velocity asymmetry,mean SSC during flood tide phase was 1.8 times higher than that of ebb tide phase.As a result,net onshore sediment flux controlled cross-shore suspended sediment transport process and salt marsh pioneer zone was generally accreting.There was significant positive correlation between total sediment flux and quartic power of maximum water depth.It indicates that tidal ranges dominate suspended sediment transport and sedimentation process in the salt marsh pioneer zone under the calm weather condition.The sedimentation rate on the adjacent mudflat was higher than the salt marsh,which induced stable accreting of salt marsh towards the sea.The wind events enhanced SSC and current velocity during the semidiurnal tides.And the remarkable onshore net sediment flux could occur on the high marsh and mudflat close to the marsh fringe during the short period under the rough weather condition.

Spatial pattern of modern sedimentation rate of Qinghai Lake and a preliminary estimate of the sediment flux

We investigated the spatiotemporal distribution of1 37Cs radioactivity in surface sediment of Qinghai Lake,and developed the spatial pattern of sedimentation rate.The1 37Cs inventory is higher near the estuary/bank area,but lower at the central lake.On the other hand,the average1 37Cs activity is lower near the estuary/bank area,but higher at the central lake.The mass accumulation rate(MAR) and the fluxes and contents of the terrestrial detritus(e.g.SiO2,Fe2O3,and Ti) are higher near the estuary/bank area,but lower at the central lake.The chemical/biogenic deposits(e.g.the autogenic carbonates) take up higher fractions at the central lake.These suggest that the spatial pattern of recent sedimentation rate is dominated by the deposition of terrestrial detritus.The average MAR(0.0337 g cm-2a-1) was estimated based on those of different cores of Qinghai Lake and was verified by a Ca mass-balance method.The fluxes of total lake sediments,terrestrial detritus,and direct atmospheric deposits were also estimated.

Effects of hydrodynamics processes on phosphorus fluxes from sediment in large,shallow Taihu Lake

The turnover of phosphorus （P） in lake sediments, a major cause of eutrophication and subsequent deterioration of water quality, is in need of deep understanding. In this study, effects of resuspension on P release were studied in cylindrical microcosms with Yshape apparatus. The results indicated that there was a positive correlation between flux of suspended substance across sediment-water interface （Fss） and the wind speed, and an increasing Fss during each wind process followed by a steady state. The maximal Fss under fight, moderate, and strong wind conditions were 299.9±41.1,573.4±61.7, and 2093.8±215.7 g/m^2, respectively. However, flux of P across sediment-water interface （Fp） did not follow a similar pattern as Fss responding to wind intensity, which increased and reached the maximum in initial 120 rain for fight wind, then decreased gradually, with maximal flux of 9.4±1.9 mg/m^2. A rapid increase of Fp at the first 30 rain was observed under moderate wind, with maximal flux of 11.2±0.6 mg/m^2. Surprisingly, strong wind caused less Fp than under light and moderate wind conditions with maximal flux of 3.5±0.9 mg/m^2. Fss in water column declined obviously during the sedimentation process after winds, but Fp varied with wind regime. No obvious difference was detected on Fp after 8 h sedimentation process, compared with the initial value, which means little redundant P left in the water column after winds.

A preliminary study on sediment flux in the Changjiang Delta during the postglacial period

The sequence boundary and maximum flooding surface of the postglacial transgressive cycle in the Changjiang Delta have been identified by 265 cores. Based on these data, the sediment amounts and the thickness-isopach maps of postglacial sedimentary cycle, transgressive and regressive successions in the Changjiang Delta have been worked out. The results show that the sediment amounts of the postglacial cycle, transgressive succession and regressive succession are 17742.2×108 tons, 9791.9×108 tons and 7950.3×108 tons, respectively. The postglacial sediments deposited in the incised valley are more than those in the two flanks, and the sediments contained in the transgressive succession are more than those in the regressive succession. The postglacial sediments deposited in the southern flank are more than those in the northern flank, and the sediments in the area seaward from the postglacial transgression maximum (PTM) of each flank are more than those in the area landward from the PTM. Considering both the possible changes of the ratio between the sediment amount remained in the modern Changjiang Delta and the sediment discharge of the Changjiang River in the postglacial period, and the changes of the sediment discharge, the authors believe that in the postglacial period, the sediment discharge of the Changjiang River is (2.36—4.86)×108 tons/a on average, totaling to (35400—70800)×108 tons, and the sediments delivered to sea and adjacent coasts are (1.18—3.54)×108 tons/a on average, totaling to (17700—53100)×108 tons.

Suspended sediment flux of river:Wavelet analysis in the Panlong basin of the Upper Red River (Honghe River),China

这份报纸把小浪分析用于检验变化趋势，多时间规模变化，在上面的红河的 Panlong 盆的推迟的沉积流动(SSF ) 的周期、突然的变化特征，中国。结果显示 SSF 从 1951 ～ 1997 增加了，但是自从 1998，衰退了。SSF 的变化把多时间规模特征和变化在不同时间时期改变了。三周期的时间规模， 4， 7 和 22 年，被决定。22 年的周期的时间规模，是在三次规模之中的最明显的，通过整个研究时期延长了，而第 4-a 7 年的时间规模在某些时间时期仅仅是明显的。分别地有 27 次越过 4 年的时间规模，越过 7 年的时间规模的 16 次和越过 22 年的时间规模的 5 次的突然的变化。根据统计的聚会和气候数据分析，我们断定人的活动是导致了多时间规模的 SSF，而是特征的变化趋势的主要原因，周期、突然的变化被气候变化主要影响。

The suspended sediment transport equation and its near-bed sediment flux

The suspended sediment transport equation and its near-bed sediment flux are one of the key problems of sediment transport research under nonequilibrium condition. Based on the three-dimensional primitive suspended transport equation, the two-dimensional suspended sediment transport equation is deduced. The derived process indicates that the physical essence of the near-bed sediment flux is right the bottom boundary condition for the suspended sediment transport equation. This paper analyzes the internal relations between the two methods of sediment carrying capacity and shear stress in common use, points out the consistency of these two methods in terms of form and physical meaning, and unifies these two methods theoretically. Furthermore, based on the analysis and comparison of the expressions of the near-bed sediment flux, this paper summarizes some problems to which attention should be paid, thus offering a novel approach to the study and the solution of the problems of suspended sediment transport and exchange flux of near-bed water sediment.

Distribution and fluxes of suspended sediments in the offshore waters of the Changjiang (Yangtze) Estuary

The offshore waters of the Changjiang Estuary are the transitional areas where river-supplied water and sediment are transported to the sea, and material exchanges occur with the neighbored Hangzhou Bay and the Jiangsu waters. Field observations of currents and sediment properties were conducted to study temporal and spatial distributions of suspended sediments under various dynamical conditions. The high sediment concentrations were found to occur in the western and southern waters of the offshore, and the low concentrations occurred in the eastern and northern waters. This pattern of the suspended sediment concentration （SSC） distribution is obviously influ- enced by the runoff and tidal current. The significant difference of along-estuary SSC distribution indicates that the SSC is reduced gradually from the west to the east, and that in the spring tide is obviously higher than in the neap tide. The methods of mechanism analysis and equal-area grids were used to calculate the suspended sediment fluxes at the typical cross sections. It was found that 44 percent of total suspended sediments from the Changjiang River were deposited in the submarine delta, and more than 27 percent of sediments were transported southernly into the Hangzhou Bay, and only 9 percent of sediments was supplied and exchanged with the northern Jiangsu waters, and about 20 percent of sediments was delivered offshore to the sea.

Using seismic surveys to investigate sediment distribution and to estimate burial fluxes of OC, N, and P in a canyon reservoir

As a high-precision survey method,seismic surveying has been increasingly applied to inland water research,although its application to artificial reservoirs has remained limited.As a special artificial water body,reservoirs have important effects on the fluvial transport of material from land to ocean,and inevitably have complex terrain which can complicate and distort the results of seismic surveys.Therefore,there are still some problems need to be resolved in the application of seismic surveys in reservoirs with complex terrain.For this study,the Dongfeng Reservoir located in the upper reaches of the Wujiang River was chosen as an example to test the seismic survey method.Our testing showed that(1)because of the complex underwater terrain,the signal-to-noise ratio of the echo signal in canyon reservoir is low,making it difficult to determine sediment layers thicknesses in some areas;and(2)due to the large spatial heterogeneity of sediment distribution,insufficient density of cross-sections can lead to inaccurate interpolation results.To improve the accuracy of calculations,a mathematical method was used.Ultimately,the total burial mass of sediment was estimated at 2.85 x 107 tons,and the average burial rates of total organic carbon,total phosphorus,and total nitrogen were estimated at 0.194,0.011,and 0.014 g cm-2 year-1,respectively.These values were close to the results of previous studies and hydrographic station data,indicating that seismic survey can be a reliable and efficient method for the mapping of reservoirs.

The Effect of Bioturbation Activity of the Ark Clam Scapharca subcrenata on the Fluxes of Nutrient Exchange at the Sediment–Water Interface

Filter-feeding shellfish are common benthos and significantly affect the biogeochemical cycle in the shallow coastal ecosystems.Ark clam Scapharca subcrenata is one of the widely cultured bivalve species in many coastal areas owing to its tremendous economic value.However,there is little information regarding the effects of the bioturbation of S.subcrenata on the fluxes of nutrient exchange in the sediment-water interface(SWI).In this regard,S.subcrenata was sampled during October 2016 to determine the effects of its bioturbation activity on the nutrient exchange flux of the SWI.The results showed that the biological activity of S.subcrenata could increase the diffusion depth and the rate of the nutrients exchange in the sediments.The bioturbation of S.subcrenata could allow the nutrients to permeate into the surface sediments at 6-10cm and increase the release rate of nutrients at the SWI.The releasing fluxes of DIN and PO43−-P in the culture area were found to be around three times higher than that in the non-cultured region.The culture of S.subcrenata has been proved to be an important contributor to nutrient exchange across the SWI in the farming area of Haizhou Bay.Nutrients exchange in the SWI contributes a part of 86%DIN,71%PO43−-P and 18%SiO32−-Si for the aquaculture farm.

Nitrogen and Phosphorus Diffusive Fluxes Across the Sediment-Water Interface in Estuarine and Coastal Tidal Flats

Nitrogen and phosphorus contents are analyzed in the overlying waters and pore waters taken from the Changjiang Estuary and Shanghai coastal tidal flats in this study. In addition, the diffusion fluxes of nitrogen and phosphorus across the sediment-water interface in tidal flats are estimated according to the nutrient concentration gradients at the interface. It has been indicated that the concentrations of ammonium, nitrite, nitrate and dissolved phosphorus in overlying waters range from 0.0082～2.56, 0.03～0.58, 0.69～5.38 and 0.035～0.53 mg/L, respectively, while 0.0025 ～ 1.35 mg/L for NH4+-N, 0. 0055 ～ 0.20mg/L for NO2--N, 0.61～1.14 mg/L for NO3--N and 0.11～0.53mg/L for DP insurface pore waters.The findings have revealed that ammonium, nitrite, nitrate and dissolved phosphorus diffusion fluxes across the sediment-water interface are between -0.024～0.99, -0.39～ -0.0019, -3.09～the source of phosphorus and an important sink for nitrogen in the waters.

Re-evaluating the vertical mass-flux profiles of aeolian sediment at the southern fringe of the Taklimakan Desert, China

Reliable estimation of the mass-flux profiles of aeolian sediment is essential for predicting sediment transport rates accurately and designing measures to cope with wind-erosion. Vertical mass-flux profiles from seventeen wind-erosion events were re-evaluated using five typical models based on observed data obtained from a smooth bare field at the southern fringe of the Taklimakan Desert, China. The results showed that the exponential-function model and the logarithmic-function model exhibited the poorest fit between observed and predicted mass-flux profiles. The power-function model and the modified power-function model improved the fit to field data to an equivalent extent, while the five-parameter combined-function model with a scale constant（σ） of 0.00001 m（different from the σ value proposed by Fryear, which represented the height above which 50% of the total mass flux occurred） was verified as the best for describing the vertical aeolian sediment mass-flux profiles using goodness of fit（R2） and the Akaike Information Criterion（AIC） values to evaluate model performance. According to relationships among model parameters, the modified power model played a prominent explanatory role in describing the vertical profiles of the observed data, whereas the exponential model played a coordinating role. In addition, it was found that the vertical profiles could not be extrapolated using the five selected models or easily estimated using an efficient model without field observations by a near-surface sampler at 0 to 0.05 m.

Exchange fluxes of nutrients between sediment and sea water in the Bohai Sea

Investigations of sediment-water fluxes of nutrients in the Bohai Sea were carried out in September - October 1998 and April - May 1999. The exchange fluxes of nutrients between sediment and sea water were determined by incubating the core-top sediments with overlying water aerated with air. The benthic fluxes of NO3- , NO2- , NH4+ , DIN, DON and TON in the first cruise and the flux-es of NO3 , NO2- , NH4+ , DIN, DON, TDN, PO43- , DOP and TDP in the second cruise were measured. The exchange fluxes of nutrients in fall were higher than in spring. The benthic nutrient fluxes represented 15% -55% of nutrient budgets in the Bohai Sea.

Nutrient Fluxes and Sediments Composition in El Mex Bay and Surround Drains, Alexandria, Egypt

The regeneration of pore water (PW) nutrients was investigated and the contribution of benthic nutrient fluxes to the overlying bottom water (BW) was examined. Dissolved inorganic nutrients (NO-2, NO-3, PO3-4 and SIO4-4) were measured in PW and BW in El Mex Bay and surround drains during spring 2010. Nutrient concentrations gradiance in PW with overlying seawater were evaluated according to Fick’s Law. Average inorganic nutrient fluxes were estimated using the pore water gradient concentration across the sediment-water interface. Calculated nutrient fluxes had averages of ﹣7.24, ﹣1.36, ﹣7.86 and ﹣1.33 in El Mex Bay. Additionally, the fluxes in the drains were ﹣34.39, ﹣32.28, ﹣53.20 and ﹣117.6 mg·m﹣2·day﹣1 for NO-3, NO-2, PO3-4 and SIO4-4, respectively. Mineralogical studies of sediment samples by using IR, X-ray analysis were carried out to identify the chemical structure of sediments. The results revealed that calcite, aragonite and quartz are the dominant minerals. On the other hand, differential thermal analysis (DTA) was used to evaluate and discuss different kinetic parameters such as Ea#, ΔG#, ΔH#, ΔS#, Z and Tm support the view of the extra stability of these sediments.

Comparison of depth-averaged concentration and bed load flux sediment transport models of dam-break flow

This paper presents numerical simulations of dam-break flow over a movable bed. Two different mathematical models were compared: a fully coupled formulation of shallow water equations with erosion and deposition terms(a depth-averaged concentration flux model), and shallow water equations with a fully coupled Exner equation(a bed load flux model). Both models were discretized using the cell-centered finite volume method, and a second-order Godunov-type scheme was used to solve the equations. The numerical flux was calculated using a Harten, Lax, and van Leer approximate Riemann solver with the contact wave restored(HLLC). A novel slope source term treatment that considers the density change was introduced to the depth-averaged concentration flux model to obtain higher-order accuracy. A source term that accounts for the sediment flux was added to the bed load flux model to reflect the influence of sediment movement on the momentum of the water. In a onedimensional test case, a sensitivity study on different model parameters was carried out. For the depth-averaged concentration flux model,Manning's coefficient and sediment porosity values showed an almost linear relationship with the bottom change, and for the bed load flux model, the sediment porosity was identified as the most sensitive parameter. The capabilities and limitations of both model concepts are demonstrated in a benchmark experimental test case dealing with dam-break flow over variable bed topography.