International Journal of Sediment Research最新文献

Lateral intakes are very important for diverting a portion of the river flow and providing the proper flow depth. In cases where small dams are used to operate and control the river's water level for the intake and to meet downstream water needs, the opening and closing of the dam gates before the construction of the intake and during its operation are important. In the current study, the problem of reducing the water head in the intake basin of the Hemmat dam pumping station, especially in the seasons of low water and the accumulation of sediment in the intake inlet of the Hemmat dam located in the Khuzestan province of Iran, has been investigated. Focusing on different arrangements of opening and closing gates, using a spur dike and flow rates of 143, 100, 62, 32, and 12 m³/s to investigate velocity changes and the depth of flow at the water inlet, computational fluid dynamics (CFD) simulations were done. With the spur dike, the water intake efficiency is increased by 384% compared to the project's current state (operation without any flow control structure), and the hydraulic conditions resulting in sedimentation are eliminated. The flow depth of the water intake channel, with the spur dike, increases by 10% compared to the condition without it. It is worth mentioning that gate management also affects water supply efficiency. The results of the current study are a good example of the successful application of computer simulations for sustainable systems engineering.

In the present era, sedimentation and bed morphology near hydraulic structures is a great concern as it affects the flow configuration and reduces the discharge capacity. Experimental investigations were done to study the flow field in the vicinity of one cycle, two cycle, and three cycle piano key weirs (PK weirs) with noses to monitor the sediment passing capacity of the weir. The three dimensional (3D) velocities were measured close to the inlet and outlet keys using an acoustic Doppler velocimeter (ADV). The velocity fields near both the inlet and outlet keys were examined, and it was found that there were considerable increases in the vertical (v-component) and lateral (w-component) velocities. Added to this, it was seen that the mean vertical velocity was more in front of the outlet key as compared to the front of the inlet key while the mean lateral and longitudinal velocities were low. The maximum velocity was observed in front of the inlet key which resulted in an increase of sediment movement over the PK weir. Furthermore, 2.6%–5.2% of the total sediment passing over the upstream portion of the weirs are flushed over the inlet key by self-cleaning. The flow field over the keys could not be accurately estimated using an ADV, possibly due to the flow complexity so computational fluid dynamics (CFD) simulations were done to understand the complex flow field for all the three PK weirs using a CFD solver which needs less computational cost and space. The widely used standard k–ε turbulence model (an eddy-viscosity model) was applied in the current numerical investigations. The numerical investigation shows that the magnitude of the velocity components was increased because of the vertical contraction in front of the sloped keys owing to very high flow immediately downstream of PK weirs.

Grainsize is among the most important parameters in aeolian research as it controls the sediment mobilization and the mode of transport. Therefore, it is a critical parameter for instance in wind erosion modeling studies which are used to analyze sand and dust storms in the Tarim Basin, an important natural hazard in this region. Spatially explicit parameterization of grain size is difficult, as the texture of the topsoil is not homogeneous across a landscape. Thus, a geomorphological classification of a Tugai landscape in the eastern Tarim Basin is developed and a stratified analysis of the grain-size distributions and the corresponding threshold friction velocities is presented. The results show that transversal dunes have the coarsest sediment in this landscape, while vegetated patches within the alluvial plain of the Tarim River are characterized by the finest sediments. The other landform classes open space, channel, and nebkha have properties between these two landform types. It is concluded that the surface sediment of a Tugai landscape in the eastern Tarim Basin shows a considerable heterogeneity. The landform-based stratification for grain-size analysis is an appropriate solution for an assessment of sediment grains.

Sediment pulses can cause relevant geomorphological alteration and fine sediment deposition, affecting the entire river ecosystem. Quantifying the impact of these events is becoming increasingly important, as sediment disturbance is predicted to intensify because of growing anthropogenic activity combined to the effects of current climate change. In this paper, the effects of a sediment pulse event on riverbed morphology and, in turn, on fish habitat availability are assessed in a regulated river, located in the southern European Alps. Specifically, four target fish species were selected: marble (Salmo marmoratus) and brown trout (Salmo trutta), grayling (Thymallus thymallus), and bullhead (Cottus gobio). The investigated event was triggered by the effects of localized landslides combined with an uncontrolled sediment release from a hydropower reservoir. A pre-post event integrated approach was applied, involving topographic surveys, fine sediment deposition measurements, and eco-hydraulic modeling. Habitat availability analysis was done using two-dimensional steady-state channel-flow simulation and standard habitat suitability modeling, with univariate suitability curves as biological input. The investigation focused on two river reaches, quite close each other, but characterized by significantly different streamflow patterns, due to the layout of the local hydropower system. The results showed that noticeable riverbed fining occurred at both study reaches after the pulse, with the maximum thickness of the fine sediment deposits up to one meter, and higher amounts of deposition detected in areas wetted at baseflow. Moreover, for both reaches, recovery to the pre-event riverbed grain-size condition occurred in about a year, but with differences related to different streamflow patterns. Pre-post topographic comparison showed that areas of erosion prevailed over areas of deposition, and fine sediment deposition was not systematically associated to the riverbed elevation raise. Simulated habitat availability was affected by both topographic changes and fine sediment deposition, with the latter predominantly impacting juveniles and the most bottom dwelling species, i.e., the bullhead. The study confirms the need for improving the management of the hydro-sedimentary regime of regulated rivers to preserve the habitat of fish species, particularly of those characterized by conservation status already endangered.

Measuring the grain size distribution (GSD) of unconsolidated particles is critical to understanding coastal spreading, riverbed dynamics, and sediment transport. The current study presents a novel gravel automatic sieving (GAS) method designed to improve the accuracy and reliability of particle size analyses. At the macroscopic, the method utilizes the convex hull property of gravel to define the maximum extent of the searched gravel, effectively reducing over and under-segmentation problems. At the microscopic, the accuracy of gravel segmentation is improved by analyzing the color space characteristics of gravel to identify the pixel patches of gravel accurately. To validate the effectiveness of the GAS method, the proposed method was tested in both the laboratory and the field. In the laboratory, four artificial samples were processed using the GAS method, and the results were compared with those obtained using the traditional sieving method. The results showed that the correlation coefficients between the GAS method and the traditional sieving method ranged from 94.3% to 97.8%, and the relative errors ranged from 5.8% to 20.9%, demonstrating the validity of the GAS method. In addition, the application of ImageJ software to manually identify the particle size method (ImageJ method) was also compared with the mechanical sieving method, and the correlation coefficient between the two methods was greater than 98.2%, and the relative error was less than 10.9%, so the ImageJ method can be used as a standardized method to measure the other methods. In the field, sixteen images taken in four different regions and at different times were analyzed using the ImageJ method as a benchmark. The performance of the automatic with image filtering (AIF), BASEGRAIN, and the GAS methods also were compared. The results show that the relative errors range from 28.1% to 94.6% for the BASEGRAIN, 16.8% to 1003.6% for the AIF method, and only 5.6% to 30.7% for the GAS method. As a result, the GAS method demonstrates higher accuracy and stability in complex environments.

In agricultural landscapes, the use of topographic index (TI) models has been common to predict the presence and extent of ephemeral gullies (EGs). However, these models face two significant challenges: (1) the accurate prediction of EGs relies heavily on a critical threshold (CT) value, which is difficult to determine optimally using existing strategies, and (2) the calibration of TI models limits their applicability on a larger scale. To address these limitations, the current study proposes two methods: (1) the division of the study area into zones based on key factors influencing gully formation, reducing the need for TI model calibration, and (2) a pixel-based binary classification approach coupled with a precision performance metric to identify the calibrated CT value within a watershed. The performance of seven TI models for predicting EG length was evaluated using local validation within zones and transferred validation between zones. Local validation demonstrated that among the TI models, modified stream power index (MSPI), stream power index (SPI), and compound topographic index (CTI), in descending order, yielded the most accurate predictions for EG length. Furthermore, the decrease in accuracy observed in the transferred MSPI model compared to the local MSPI model supported the study's hypothesis that dividing a large-scale area into distinct zones with varying topographic and climatic characteristics enables the determination of a CT value specific to each zone. Soil loss rates due to EGs ranged from 0.36 to 1 kg/m² yr, aligning with findings from similar global studies. These findings offer valuable insight that can be integrated into comprehensive watershed and soil erosion models.

Vegetation-induced sedimentary structures (VISS) are bed features resulting from flow-vegetation feedback and turbulence induced by vegetation at riparian sites. Generally, these sedimentary structures commence at the individual plant level, but sediment accumulation over time may lead to the formation of fluvial islands. Additionally, riparian vegetation exposed to current may provoke local scouring. However, little research has been done on how the permeability of plants affects flow fields and sedimentary processes. Therefore, the main aim of the current study is to experimentally investigate patterns of local scour and deposition around artificial obstacles with six different levels of porosity, using a systematically designed flume experiment. Two experimental setups were implemented, with sediment transport occurring either as bed load or in suspension. Porosity, as a measure of the volume of porous space to bulk volume, was determined using optical porosity which was estimated from digital photographs. Furthermore, VISS of individual P. nigra shrubs were investigated at different seasonal stages (leafless and full foliage) at the Loire River, France, for comparison. Results show that increasing porosity caused a reduction in sediment deposition from suspension and locally scoured bed load sediment. A threshold value for optical porosity was determined, at which point a prolonged area of flow calm develops behind the barrier, promoting the accumulation of suspended sediment and suppressing local scour caused by bed load transport. An empirical model is presented, which assesses sediment erosion and deposition volumes at porous obstructions, considering (a) the flow-exposed surface area, (b) the obstruction's optical porosity, and (c) the intensity of the incoming flow. On the field scale, local scour holes were identified at P. nigra shrubs where flood-caused debris obstructions were stuck at their front, lowering the obstruction's porosity and encouraging local scour processes.