International Journal of Sediment Research最新文献

Local scour at piers is one of the primary causes of bridge failures. The prediction method for the temporal evolution of local scour depth at bridge piers during floods was investigated based on the law of conservation of energy. The energy transfer process between water flow and sediment during the local scour process at bridge piers was theoretically analyzed based on the current understanding of the mechanism of local scour. The results show that there is a dynamic equilibrium relation between the energy loss of water flow and the energy gain of eroded sediment during the local scour process. This relation is applied to establish a mathematical model for predicting the temporal evolution of scour depth. This model has only one parameter, which is the energy transfer efficiency between the water flow and the eroded sediment. The energy transfer coefficient is mainly determined by the flow intensity under clear-water scour conditions, and an empirical formula for calculating it is obtained. The proposed model was evaluated using measured data of local scour depth under both well-controlled flows and natural floods. The results show that the model is able to provide satisfactory predictions and its performance can be further improved by including more sophisticated methods for determining the critical velocity for incipient scour. Meanwhile, the performance of the model is insensitive to the possible uncertainties introduced when determining the energy transfer coefficient. The research results indicate that it is feasible to establish a theoretical prediction model for accurately forecasting the local scour depth at bridge piers.

River levees are subject to bioturbation by various animals which can actively excavate into earthen structures producing an internal erosion that, during the passage of a flood, can grow in time making the levee unstable. This phenomenon can lead to river levee breaching and, as a consequence, collapse, even for relatively minor flood events. A well-known animal burrower is represented by the North American crayfish Procambarus clarkii (P. clarkii), an invasive species in Europe, mainly introduced for commercial purposes, causing a decline in biodiversity and profound habitat changes. The physical damages caused by P. clarkii on levees and banks, such as in rice fields, irrigation ditches, and small channels, have not been fully studied and behavioral components underlying this impact are mostly occasional. To understand the impact of burrowing activity on the seepage process, a field survey was done in a drainage channel in Tuscany, Italy, to evaluate the density and geometry of the internal burrows that were excavated by the crayfish. Based on these observations and some previous laboratory experiments, three dimensional (3D) numerical simulations of the seepage processes were done inside burrowed levees. Numerical results allowed the increase in the hydraulic vulnerability of levees to the process of internal seepage to be disclosed. In particular, for a given river water level, the reduction of the time scale for the phreatic line to reach the levee field side appears to be a function of a quantity here defined as the burrow hydraulic gradient. This quantity is here defined as the ratio between the hydraulic head inside the burrow and the horizontal distance from its end to the field side of the levee. Moreover, a comparison between the 3D with the analogous more common two dimensional (2D) numerical simulations illustrated the schematization which is better suited for describing the seepage processes when animal burrows, not only by crayfish, are present.

The Xiangjiaba and Xiluodu reservoirs, located on the upper Yangtze River, have been operational and the changes in the downstream river regime and waterway conditions have attracted great attention. A two-dimensional horizontal (2DH) flow–sediment mathematical model of the Shuifu to Lanjiatuo reach (Shuilan reach) downstream of the Xiangjiaba Dam was developed. The spatio-temporal characteristics of sediment scouring and siltation after completion of the cascade of reservoirs were simulated using the model, and then the river regime changes in several typical reaches as well as their possible impacts on navigation channels were analyzed. The results show that, after operation of the cascade of reservoirs, the downstream channel is in the state of scour. The general change of the river regime is that the flow in curved reaches tends to be straight though the river pattern still remains curved. Sub-branches tend to experience deposition, while the main channel will be scoured deeper, which can help to increase the navigation depth in the shoals in the transition sections. Deposition in some sections could result in new shoals. In addition, the bottom elevation difference between floodplains and channels will increase, which could aggravate local adverse flow patterns; therefore, navigation conditions in torrential shoals will tend to deteriorate.

Lake eutrophication in cold and arid regions is showing a deepening trend in recent years, posing a serious threat to the regional ecological environment. The occurrence characteristics, bioavailability, sorption–desorption characteristics, and release risk of sediment nitrogen in the Ulanor Wetland, located in the Hulun Lake basin of China, were investigated by combining field investigation, laboratory simulation experiments, and multiple technologies, including diffusive gradients in thin films and high-resolution dialysis technology. The total nitrogen (TN) in the water overlying the sediment bed (i.e., overlying water) ranged from 1.44 to 2.65 mg/L. Dissolved inorganic nitrogen was the main form of TN in overlying water, and ammonia nitrogen (NH₄⁺–N) in the pore water at the sediment–water interface was higher than that in the overlying water. Surface sediment TN content ranged from 695.37 to 2,344.77 mg/kg, with acid-dissolved nitrogen as the main component, and can cause the lowest level of ecotoxic effect. The maximum and equilibrium adsorption amounts of sediment NH₄⁺–N ranged from 0.269 to 1.017 mg/g and 0.0132–0.0382 mg/g, respectively. The bioavailability and transport capacity of sediment nitrogen were relatively weak, but a release risk was still observed.

Coastal wetlands are seen as efficient coastal stabilizers and provide an optimal natural ecosystem for the sequestration and storage of carbon. Thus, it is critically important for scientists and environmental managers to understand the future dynamics of coastal wetlands. The understanding of yearly to decadal development in coastal ecosystems can assist in the coastal management activity, to sustain biodiversity. In the current study, high-resolution granulometric analysis of a back-barrier salt-marsh deposit of tropical barrier estuary environments at Chandipur, India, is utilized to provide an overview of the mesoscale geomorphic processes and history of changing sediment dynamics. The multivariate statistical examination with coefficients of probability density functions and compositional data analysis helps to determine the four lithofacies of the deposit. Granulometric analysis combined with satellite image analysis reveals that relatively coarser facies were deposited during the incipient stage of the barrier development, when the marshland vegetation was relatively less dense as suggested by the lower normalized difference vegetation index (NDVI) and the saline sea water easily drowned the area and saline sediment was deposited. After rapid marsh accretion, the flow dynamics shifted to a negligible flow component in the final stage when finer facies were deposited in vegetated marshland, and the organic carbon concentration increased up to 3.5%. As plant organic matter and sediment continuously accumulates in this marshland, elevation capital grows and the marsh continues to develop and expand, reaching a densely vegetated marsh with a considerable increase in NDVI values. The findings of this multiproxy study, in conjunction with multivariate statistical analysis, provide valuable insight into the characteristics of accretion in a tropical saltmarsh, which is unique in such a geological setting.

The Qingshuigou Channel, as the current tail channel of the Yellow River, formed by the diversion of the Diaokou River in 1976, has undergone a particularly dramatic spatio-temporal evolution, and its evolution processes and the underlying mechanisms are still unclear. On the basis of the flood season cross section data for the river downstream of the Lijin Hydrological Station from 1976 to 2017, the current study calculated the main channel morphological characteristics of the tail channel in different reaches using a reach-scale morphological parameter calculation method and K-means clustering analysis. An elevated riverbed index was proposed to identify the elevated riverbed situation of the river channel. The results show that from 1976 to 2017, the bankfull area experienced repeated processes of decrease and increase, and the main channel morphology gradually changed from wide and shallow to narrow and deep over time. For most of the time period, the conveyance capacity of the main channel gradually decreased from upstream to downstream. The elevated riverbed situation gradually became more severe along the river reach from 0 to 85 km away from Lijin, but was less severe in the reach more than 85 km downstream of Lijin. The most severe elevated riverbed situation appeared mainly in the range of 71–83 km below Lijin in 1991–1995. When the sediment-carrying capacity of the water flow was strong, the bankfull area of the main channel increased, and the elevated riverbed situation was alleviated. River channel projects have helped to maintain the narrow and deep shape of the main channel, but the installation of farm dikes have aggravated the elevated riverbed situation. At the same time, extension and diversion of the tail channel have changed the erosion base level, greatly affecting the evolution of the channel morphology. The current study has provided a typical case for exploring the processes and mechanisms of tail channel evolution.

Water environment numerical models considering detailed hydrodynamic processes are effective tools to better understand the pollutant transport and transformation mechanisms and the influences of sediment and suspended sediment on pollutants in rivers in complex terrain. However, these models can hardly achieve simultaneous high-efficiency and high-accuracy simulation of large-area rivers in complex terrain. Therefore, a high-resolution water quality model was developed coupled with a sediment and suspended sediment module (GAST). The Compute Unified Device Architecture (CUDA) parallel computing architecture and robust model algorithms were used, and the model performance and functionality were improved. This model was based on detailed physical processes, while water environment parameter spatial heterogeneity also was considered. A simulation function of multiphase pollutant transport and mutual transformation was established by solving the pollution adsorption kinetic equation applicable to high-resolution terrain. The transport and mutual transformation processes of multiphase pollutants in still water and steady uniform flow were verified by considering the Nash–Sutcliffe efficiency (NSE) coefficient which exceeded 0.99. The validated high-resolution water quality model was applied to simulate a river network water environment in a sulfurous iron ore area, and the numerical results for the sulfate ion concentration spatial distribution and pollution sources of sulfate ions in the sediment and water phases were explored. The results show that the concentration of sulfate ions in the Xiaowenyu River varies between 120 and 180 mg/L. The contribution rates of the 5 tributaries with slag heaps in the lower reaches to the sulfate ion load in the Xiaowenyu River followed the order of Guojiagou (15.7%) > Baoquansi (14.6%) > Zhuyuangou (9.2%) > Qingshigou (2.8%) > Sunjiagou (1.4%). On an RTX30700d computer, only 0.55 h was needed to simulate the hydrodynamic and water quality evolution process involving 653,112 cells for a 6-h model setting. The model attained a high computational efficiency and high operation speed. This study provides a reliable tool for further study of river pollution mechanisms and river water environmental management.

Black carbon (BC), primarily originating from fossil fuel and biomass combustion, holds significance for global carbon cycling, climate change, and human health. Despite a lake's role as a carbon sink, detailed information about BC sedimentary burial flux and sink in its sediment remains insufficiently explored. The current study investigates the distribution, sources, and burial flux of BC and its subtypes (char and soot) in the surface sediment of Daye Lake, the largest lake in Huangshi City, central China. BC concentrations in the sediment ranged from 0.10 to 3.60 mg/g, corresponding to 0.40%–17.02% of organic carbon (OC). Higher values of BC and BC/OC observed in the western region suggest direct terrestrial input via river discharge and surface runoff, influenced by anthropogenic activities. In contrast, variations in char/soot ratios reflect diverse combustion sources and hydrological dynamics in different regions. The indications from BC/OC and char/soot ratios imply that fossil fuel combustion is the predominant sources. The weak correlations between BC and OC suggest that they may come from different sources or undergo different processes that affect their distribution in the lake sediment. However, a stronger correlation was observed between BC and soot, as well as between char and soot, indicating potential similarities in their input pathways. The BC burial flux displays notable variations across the lake, ranging from 0.69 to 24.07 g/m²/yr, with elevated values observed in the western region. The BC sink in the sediments of Daye Lake was estimated to be 0.635 Gg/yr. Though locally small, it significantly contributes to the broader picture of BC burial in Chinese lakes and the global distribution of BC in lake ecosystems.