Numerical study of three-dimensional wave-induced longshore current's effects on sediment spreading of the Huanghe River mouth

A three-dimensional wave radiation stress is introduced into the hydrodynamic sediment coupled model COHERENS-SED, which has been developed through introducing wave-enhanced bottom shear stress, wave dependent surface drag coefficient, wave-induced surface mixing, SWAN, damping function of sediment on turbulence, sediment model and depth-dependent wave radiation stress to COHERENS. The COHERENS-SED is adopted to study the effects induced by wave-induced three-dimensional longshore current on suspended sediment spreading of the Huanghe River （Yellow River） mouth. Several different cases divided by setting different wave parameters of inputting boundary waves are carried out. The modeling results agree with measurement data. In terms of simulation results, it is easy to know that three-dimensional wave radiation stress plays an obvious role when inputting boundary wave height is stronger than 3 m. Moreover, wave direction also affects the sediment spreading rules of the mouth strongly too.

The Shengli I Point Bar on the Yellow River Delta: Three-Dimensional Structures and Their Evolution

Point bars are well developed on the Yellow River delta, an~ which theShengli I point bar is the most typical. The point bar, being about 4 km in length and several tensto more than 100 meters in width, is located on the south side of the Shengli Bridge in KenliCounty, Dongying, Shandong. It is a typical fine-grained point bar with silt, which is predominant,some clay and minor plant debris and clay boulders. The Shengli I Point bar has complicated 3-Dstructures. Firstly, in a plane view, it comprises mainly eight sedimentary units, bar edge, baredge, bar platform, bar plain, bar channel, bar gully, bar pond and bar bay, developing side by sideand superimposed one by one m a complex way. Secondly, its vertical structures are very complex dueto the partial superimposition of the 8 sedimentary units. Besides hydatogenesis, very intensivewind erosion, eolian, ice and meltwater actions are also visible on the Shengli I point bar. Thecomplex form is made even more complicated because of the above co-actions.

Three-Dimensional Water-Quality Simulation for River Based on VOF Method

In the present study, considering the transport and transformation processes of variables, a threedimensional water quality model for the river system was established, which coupled the volume of fluid(VOF) method with the k-ε turbulence mathematical model. Then, the water hydrodynamic characteristics and transport processes for BOD_5, NH_(3^-)N and TP were analyzed. The results showed that the water surface of convex bank was a little lower than that of concave bank due to the centrifugal force near the bend, and most concentrations were inferior to the type Ⅴ standard indexes of surface water environmental quality. The model validation indicated that the errors between the simulated and monitored values were comparatively small, satisfying the application demands and providing scientific basis and decision support for the restoration and protection of water quality.

Land use and cover change and influencing factor analysis in the Shiyang River Basin,China

Land use and cover change(LUCC)is the most direct manifestation of the interaction between anthropological activities and the natural environment on Earth's surface,with significant impacts on the environment and social economy.Rapid economic development and climate change have resulted in significant changes in land use and cover.The Shiyang River Basin,located in the eastern part of the Hexi Corridor in China,has undergone significant climate change and LUCC over the past few decades.In this study,we used the random forest classification to obtain the land use and cover datasets of the Shiyang River Basin in 1991,1995,2000,2005,2010,2015,and 2020 based on Landsat images.We validated the land use and cover data in 2015 from the random forest classification results(this study),the high-resolution dataset of annual global land cover from 2000 to 2015(AGLC-2000-2015),the global 30 m land cover classification with a fine classification system(GLC_FCS30),and the first Landsat-derived annual China Land Cover Dataset(CLCD)against ground-truth classification results to evaluate the accuracy of the classification results in this study.Furthermore,we explored and compared the spatiotemporal patterns of LUCC in the upper,middle,and lower reaches of the Shiyang River Basin over the past 30 years,and employed the random forest importance ranking method to analyze the influencing factors of LUCC based on natural(evapotranspiration,precipitation,temperature,and surface soil moisture)and anthropogenic(nighttime light,gross domestic product(GDP),and population)factors.The results indicated that the random forest classification results for land use and cover in the Shiyang River Basin in 2015 outperformed the AGLC-2000-2015,GLC_FCS30,and CLCD datasets in both overall and partial validations.Moreover,the classification results in this study exhibited a high level of agreement with the ground truth features.From 1991 to 2020,the area of bare land exhibited a decreasing trend,with changes primarily occurring in the middle and lower reaches of the basin.The area of grassland initially decreased and then increased,with changes occurring mainly in the upper and middle reaches of the basin.In contrast,the area of cropland initially increased and then decreased,with changes occurring in the middle and lower reaches.The LUCC was influenced by both natural and anthropogenic factors.Climatic factors and population contributed significantly to LUCC,and the importance values of evapotranspiration,precipitation,temperature,and population were 22.12%,32.41%,21.89%,and 19.65%,respectively.Moreover,policy interventions also played an important role.Land use and cover in the Shiyang River Basin exhibited fluctuating changes over the past 30 years,with the ecological environment improving in the last 10 years.This suggests that governance efforts in the study area have had some effects,and the government can continue to move in this direction in the future.The findings can provide crucial insights for related research and regional sustainable development in the Shiyang River Basin and other similar arid and semi-arid areas.

The energy budget under the influence of topography in the Zhujiang River Estuary in China

The Zhujiang River （Pearl River） Estuary （ZRE） is a very complicated and large-scale estuarine system in China. It consists of two parts： the river networks and the estuarine bays. Not only is the network system one of the most complicated in the world, but also each estuarine bay has a very special morphodynamic feature due to the geological settings. Morphological boundary conditions have direct effects on the energy dissipa- tion and balance. On the basis of a three-dimensional （3-D） barotropic model whose domain includes the river networks and the estuarine bays, the energy budget is discussed under the influence of topography in the ZRE. The elevation and discharge of this model are validated by the observations collected in July 1999 and February 2001. The results show that （1） the source of energy in the ZRE is mainly generated by tides and river runoffs, which have an obvious seasonal change, and （2） there are some typical hotspots where the energy dissipation is 1-2 orders higher than those in the immediate upstream and downstream sections in the ZRE. These hotspots are linked with the small-scale dynamic structures （SSDS） and morphological units. On the basis of the characteristics of the morphology and the energy dissipation, the hotspots can be catego- rized into three types： the outlet of the ZRE, the meandering river, the branch and junction.

Architectural Model of a Dryland Gravel Braided River,based on 3D UAV Oblique Photogrammetric Data:A Case Study of West Dalongkou River in Eastern Xinjiang,China

Three-dimensional unmanned aerial vehicle(UAV)oblique photogrammetric data were used to infer mountainous gravel braided river lithofacies,lithofacies associations and architectural elements.Hierarchical architecture and lithofacies associations with detailed lithofacies characterizations were comprehensively described to document the architectural model,architectural element scale and gravel particle scale.(1)Nine lithofacies(i.e.,Gmm,Gcm,Gcc,Gci,Gcl,Ss,Sm,Fsm and Fl)were identified and classified as gravel,sand and fine matrix deposits.These are typical depositional features of a mountainous dryland gravel-braided river.(2)Three architectural elements were identified,including channel(CH),gravel bar(GB)and overbank(OB).CH can be further divided into flow channel and abandoned channel,while GB consists of Central Gravel bar(CGB)and Margin Gravel bar(MGB).(3)The gravel bar is the key architectural element of the gravel braided river,with its geological attributes.The dimensions of GBs and their particles are various,but exhibit good relationships with each other.The grain size of GB decreases downstream,but the dimensions of GB do not.The bank erosion affects the GB dimensions,whereas channel incision and water flow velocity influence the grain size of GB.The conclusions can be applied to the dryland gravel braided river studies in tectonically active areas.

Modeling transportation of suspended solids in Zhujiang River estuary, South China

A three-dimensional transportation model for suspended solids (SS) in Zhujiang (Pearl) River estuary, South China, was developed by coupling with a three-dimensional hydrodynamic model. The model was validated using hourly measured data of sediment contents during 25–26, July 1999. The results showed that modeled contents matched well with measured ones and that the modeled top layer distribution agreed with the remotely sensed image of suspended solids in summer. The modeled results showed clearly the layers of sus- pended solids in depth, with larger sediment contents in lower layers though in the interface between salt water and freshwater the lowest contents appeared in middle layer. In overall, the suspended solids inflow from 8 rivers, transport southwestward, and carried by strong coastal flow in Zhujiang River estuary. Contours of sediment contents in the estuary spread further to the open sea during ebb tide rather than flood tide which reflects that the suspended solids in the estuary are land sourced.

EXPERIMENTS OF THREE-DIMENSIONAL FLOW STRUCTURE IN BRAIDED RIVERS

The braided river is a typical river pattern in nature, but there is a paucity of comprehensive data set describing the three-dimensional flow field in the braided river. A physical model experiment was used to study the flow characteristics in the typical braided river with a mid-bar between two anabranches. In the experiment, two kinds of mid-bar with the ratios of its length to maximal width of 3 and 5 were considered. Moreover, the mid-bar could be moved to adjust the width of two anabranches. The detailed measurements of velocity were conducted using an acoustic Doppler velocimeter over a grid defined throughout the whole braided river region, including the bifurcation, two anabranches and the confluence. In two kinds of mid-bar braided models, a separation zone was observed in the anabranch of the model in which the ratio of length to maximal width of mid-bar is 3, however the separation zone was not found in another model in which the ratio is 5. In addition, the opposite secondary cells were observed at the bend apex of anabranch in two models, and different longitudinal velocity distributions in the entrance region of anabranch account for this opposite flow structure. Finally, turbulent kinetic energy were shown and compared in different situations. The high turbulence occurs at the place with strong shear, especially at the boundary of the separation zone and the high velocity passing flow.

Redefinition to bilayer osmotic pump tablets as subterranean river system within mini-earth via three-dimensional structure mechanism

Defining and visualizing the three-dimensional(3 D) structures of pharmaceuticals provides a new and important tool to elucidate the phenomenal behavior and underlying mechanisms of drug delivery systems. The mechanism of drug release from complex structured dosage forms, such as bilayer osmotic pump tablets, has not been investigated widely for most solid 3 D structures. In this study, bilayer osmotic pump tablets undergoing dissolution, as well as after dissolution in a desiccated solid state were examined, and visualized by synchrotron radiation micro-computed tomography(SR-μCT). In situ formed 3 D structures at different in vitro drug release states were characterized comprehensively. A distinct movement pattern of NaCl crystals from the push layer to the drug layer was observed, beneath the semi-permeable coating in the desiccated tablet samples. The 3 D structures at different dissolution time revealed that the pushing upsurge in the bilayer osmotic pump tablet was directed via peripheral“roadways”. Typically, different regions of the osmotic front, infiltration region, and dormant region were classified in the push layer during the dissolution of drug from tablet samples. According to the observed3 D microstructures, a “subterranean river model” for the drug release mechanism has been defined to explain the drug release mechanism.

THREE-DIMENSIONAL MESOSCALE MODELING OF METEOROLOGICAL FIELDS OVER ZHUJIANG(PEARL)RIVER DELTA

The CSU-RAMS-2A was used to simulate the meteorological fields over the Zhujiang River Delta in South China. Initialized from a horizontally homogeneous atmosphere,real topography and inhomogeneous surface boundary condi- tions,the model was run with thermal and terrain forcing.The modeling results of winter and summer cases are com- pared with those observed.The similarity of the predicted distributions of winds,temperatures and humidities to the ob- served patterns permits us to conclude that the mesoscale distribution of meteorological elements for the two study dates is the result of the thermal and dynamical forcing by the underlying surface and topography.

Optical properties of estuarine dissolved organic matter isolated using cross-flow ultrafiltration

Dissolved organic matter （DOM） from freshwater, mid-salinity, and seawater endmember samples in the Jiulong River Estuary, China were fractionated using cross-flow ultrafiltration with a 10-kDa membrane. The colloidal organic matter （COM; 10 kDa-0.22 pm） retentate, low molecular weight （LMW） DOM （〈10 kDa） permeate, and bulk samples were analyzed using absorption spectroscopy and three-dimensional fluorescence excitation-emission-matrix spectroscopy. The UV-visible spectra of COM were very similar to those obtained for permeate and bulk samples, decreasing monotonically with increasing wavelength. Most of the chromophoric DOM （CDOM, expressed as the absorption coefficient a355） occurred in the LMW fraction, while the percentage of CDOM in the colloidal fraction was substantially higher in the freshwater endmembet （13.4% of the total） than in the seawater endmember （6.8%）. The bulk CDOM showed a conservative mixing behavior in the estuary, while there was removal of the COM fraction and a concurrent addition of the permeate fraction in the mid-salinity sample, implying that part of the colloidal CDOM was transformed into LMW CDOM. Two humic-like components （CI： 〈250, 325/402 nm; and C2： 265, 360/458 nm） and one protein-like component （C3：275/334 nm） were identified using parallel factor analysis. The contributions of the C1, C2, and C3 components of the COM fraction to the bulk sample were 2.5%-8.7%, 4.8%-12.6%, and 7.4%-14.7%, respectively, revealing that fluorescent DOM occurred mainly in the LMW fraction in the Jiulong River Estuary. The C1 and C2 components in the retentate and permeate samples showed conservative mixing behavior, but the intensity ratio of C2/C1 was higher in the retentate than in the permeate fractions for all salinity samples, showing that the humic component was more enriched in the COM than the fulvic component. The intensity ratio of C3/（C 1 ＋C2） was much higher in the retentate than in the permeate fraction for mid-salinity and seawater samples, revealing that the protein-like component was relatively more enriched in COM than the humic-like component. The contribution of the protein-like component （C3） to the total fluorescence in the retentate increased from 14% in the freshwater endmember to 72% for the seawater endmember samples, clearly indicating the variation of dominance by the humic-like component compared to the protein-like component during the estuarine mixing process of COM.

Three-Dimensional Urban Thermal Effect across a Large City Cluster during an Extreme Heat Wave:Observational Analysis

Given extensive and rapid urbanization globally,assessing regional urban thermal effects(UTE)in both canopy and boundary layers under extreme weather/climate conditions is of significant interest.Rapid population and economic growth in the Yangtze River Delta(YRD)have made it one of the largest city clusters in China.Here,we explore the three-dimensional(3D)UTE in the YRD using multi-source observations from high-resolution automatic weather stations,radiosondes,and eddy covariance sensors during the record-setting heat wave(HW)of July-August 2013.It is found that the regional canopy layer UTE is up to 0.6-1.2℃,and the nocturnal UTE(0.7-1.6℃)is larger than daytime UTE(0.2-0.5℃)during the HW.The regional canopy layer UTE is enhanced and expanded northwards,with some rural sites contaminated by the urban influences,especially at night.In the boundary layer,the strengthened regional UTE extends vertically to at least 925 hPa(~750 m)during this HW.The strengthened 3D UTE in the YRD is associated with an enlarged Bowen ratio difference between urban and non-urban areas.These findings about the 3D UTE are beneficial for better understanding of the thermal environment of large city clusters under HW and for more appropriate adaption and mitigation strategies.

SIGMA-COORDINATE NUMERICAL MODEL FOR SIDE-DISCHARGE INTO NATURAL RIVERS

Due to large topography slopes in natural rivers, pollutant concentration embodies a property of three-dimensional distribution when wastewater is discharged from effluents along the bank. With the sigma coordinate along the vertical dimension fitted to both the moving free surface and the bed topography, a three-dimensional numerical model was developed in the present work to address pollutant transport processes in the above-mentioned cases. To avoid the reduction in accuracy caused by spurious diffusion in the case of steep bottom slopes, a formula for horizontal diffusion in the sigma coordinate system was derived. A case study for the side discharge into a straight open-channel flow shows that numerical results are verified well by experimental data. Furthermore, the present model is also verified by the simulation of discharging wastewater from Fuling Phosphorus Factory effluent into the Three Gorges Reservoir and the agreement between the numerical simulation results and field observation data is satisfactory. The change of the mixing zone scope in the water surface versus the layers along the vertical dimension was also discussed in detail. The study shows that a more realistic calculation for pollutant discharge has been provided by the present model than by the depth-average model which predicts an unrealistically smaller mixing zone.

Spectral characteristics of dissolved organic matter in sediment pore water from Pearl River Estuary

As key parts of land-sea transition zones,estuary ecosystems play a very important role in the ocean carbon cycle processes.The sources,degradation,and preservation of dissolved organic matter(DOM)in estuaries have long been the subject of intense study.To examine the aforementioned issues,this study examined three-dimensional fluorescence spectroscopy and ultraviolet-visible absorption spectroscopy to determine the spatial distribution and sources of DOM in the pore water of three sedimentary cores from the Pearl River Estuary(S1,S2 and S3,with increasing salinity).Using the parallel factor analysis(PARAFAC)method to analyze the three-dimensional fluorescence spectrum data,five fluorescent components were obtained—three humic-like components(C1,C3,and C4),and two protein-like components(C2 and C5).C2 exhibited a significant positive correlation with the sediment microbial deoxyribose nucleic acid(DNA)concentration(R~2=0.69,P<0.01),indicating that the protein-like component C2 might be derived from the catabolism of in situ microbes.C5 displayed a relatively weak correlation with DNA concentration(R~2=0.40,P<0.05),presumably due to the incorporation of phenolic compounds,which have a fluorescence peak very similar to that of protein-like components.The source of humic-like fluorescent components is extremely complex.The content at station S1 was relatively high(1.45–8.83 R.U.),which implies that terrestrial inputs had a significant influence.The three humic-like components showed similar distributions at S2 and S3,and the fluorescence intensity was rather low;this result indicates that the DOM at these two stations was more likely affected by the metabolism of algae and microorganisms.The humification index(HIX)and the fluorescence intensity of protein-like components increased and decreased,respectively,with depth.There was a significant positive correlation between the relative content of protein-like components and the spectral slope ratio(SR),which indicates that DOM transitioned from low-molecular-weight protein-like components in the surface sediment to high-molecular-weight humic-like components in the subsurface.This study provides valuable information for understanding the pore water size/reactivity(PWSR)model of DOM and its biochemical processes occurring in estuary sediments.

多技术融合的河道地形测量方法及实施应用

针对近岸区域地形探测及数据处理过程中存在数据不连续、精度及垂直基准难以统一等问题,本文提出一种融合航空遥感、机载LiDAR、GNSS-RTK,及水上水下一体化测量等技术的空地水一体化协同测绘方法,并以北江干线三维地形测量工程为例,阐述该方法的应用过程实践,为水域地形测量在测量效率、精度与数据质量等方面的提升开拓了新的解决思路。

CALCULATION OF FLOW FIELD AND ANALYSIS OF SPAWNING SITES FOR CHINESE STURGEON IN THE DOWNSTREAM OF GEZHOUBA DAM

The Chinese sturgeon （Acipenser Sinensis） is one of the unique and important fishery resources in China. Since the construction of the Gezhouba Dam, the traditional migration route of the sturgeon has been blocked; consequently, the length of natural spawning sites is reduced from 800 km in the past to less than 5 km at present. As an endangered species, the Chinese sturgeon has become one of the most conserved aquatic species. In this article, the flow field of its spawning states in the downstream of Gezhouba Dam was simulated and analyzed using N-S equations and k-ε turbulence model. Volume Of Fluid （VOF） method with the Finite Volume Method （FVM） was used to simulate the water-air two-phase flow to examine the computed area. On the basis of the ecological-hydraulic characteristics of Chinese sturgeon, the features of the flow field were investigated to provide theoretical support for the proper management of the Three Gorges Reservoir.