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Flooding of water, sediment, and driftwood and its associated landform changes often occurs downstream of debris-flow deposition zones in small, mountainous river basins. This type of flooding occurs due to a sudden decrease in the sediment transport capacity of river channels, resulting in considerable damage. Despite the significant need for appropriate countermeasures to mitigate damage, it has been a challenge to plan and implement these across all river basins at risk of these hazards. However, if a simple but reliable tool is available to identify hazardous areas in advance, this would be extremely useful for prioritizing such areas and designing and implementing the required measures. To this end, this paper examines the geomorphic characteristics of recent flood events in Japan and proposes a method for identifying hazardous areas due to inundation by flood flows with sediment. We first explain the occurrence of sediment inundation by focusing on longitudinal changes in sediment transport capacity using the geomorphic indicator defined as the product of the drainage area A and bed slope i. In addition, we investigate the longitudinal profiles of the sediment transport capacity along the study channels using a one-dimensional governing equation for flood flows and, based on the results, discuss that finding that the computed longitudinal profiles of the sediment transport capacity are consistent with the longitudinal distribution of the A i . Our findings indicate that the A i is an effective indicator for identifying areas prone to inundation by flood flows with sediment. [ABSTRACT FROM AUTHOR]

The present study discusses flood hazard characteristics in the lower reaches of the West Rapti River based on the results obtained from field surveys and numerical computations using depth averaged 2-D numerical models for flood flow and associated sediment transportation. To evaluate the inundation process with sediment erosion and deposition in the floodplain, a new erosion term was introduced into the mass conservation equations for suspended sediment and bed sediment. The results obtained from numerical computations indicated that field data on the spatial distributions of depths for inundation, and sediment erosion and deposition can be evaluated by the numerical model. Thus, numerical predictions were performed for the inundated areas, and the accumulated volumes of sediment erosion/deposition for floods with return periods of 50, 100, and 200 years, as a step towards damage assessment and risk assessment due to floods with active sediment transportation in the floodplains. [ABSTRACT FROM AUTHOR]

The Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) model integrated with the Volume of Fluid (VOF) method is applied to study the complex gas-fluid-particle coupled system. To enhance the model's feasibility, the efficiency and accuracy improvement approaches are implemented into the model, including the coarse-grained method, porous medium replacement and semi-resolved method. To validate the effectiveness and accuracy of the model, simulations of the particle water entry and dam break scenarios are conducted, Subsequently, the VOF-CFD-DEM model is utilized to study the sediment transportation under breaking waves. A comparison of various turbulence models reveals that the stabilized k - ω model can simulate the breaking wave with acceptable efficiency and accuracy. The study examines the flow characteristics, forces acting on slopes, and typical sediment movements, providing detailed case studies and data relevant to gas-fluid-particle systems. This work extends the application of the VOF-CFD-DEM model to extreme conditions in ocean engineering, offering a mesoscopic perspective on complex engineering challenges. [ABSTRACT FROM AUTHOR]

The step-pool structure is a typical riverbed structure with efficient energy dissipation in mountain rivers, which promotes channel stability by consuming flow energy and increasing resistance. Channel erosion was simulated by flume experiments to explore the mechanism and effect of the step-pool structure on channel stability, to provide a scientific and technical reference for energy dissipation and disaster reduction in mountain rivers. The results show that the step-pool structure can effectively consume flow energy, inhibit sediment transportation and improve flow resistance, thus effectively controlling stream bed incision and slope failure. With the step-pool structure, the Darcy-Weisbach coefficient of the channel increases by approximately 4 times as much as that in tests without this structure, and the time-averaged sediment transportation rate is reduced by 20%—66%, however, the effect of the step-pool structure in stabilizing the channel bed decreases with increasing flow discharge. With same height/length of the steps (0.1), the structure shows a similar effect in improving channel stability. The stability of the step-pool structure is the key condition of channel stability, and it is necessary to prevent the structure from being damaged step by step in practical application. [ABSTRACT FROM AUTHOR]

Rich ecosystems such as estuaries and brackish lakes are vulnerable to the effects of human activities and are prone to environmental changes. In particular, the salt environment, which is the backbone of the environment, might be affected not only by direct modifications such as dredging but also in ways that were not initially envisioned. Ichkeul Lake, located in the northern part of Tunisia, is a shallow brackish lake registered as a UNESCO World Natural Heritage Site. The construction of reservoirs upstream of the inflowing river in the 1980s reduced the amount of freshwater inflow. That only had been thought to be the cause of the increase in salinity in Ishkeul Lake. On the other hand, the sedimentation in the reservoirs upstream was remarkable, and the supply of sediment from the reservoirs upstream to the Ichkeul Lake was stopped. Changes in sediment outflow may have reduced lakebed altitude and enhanced seawater intrusion. However, the environmental protection measures for the lake so far have focused only on improving the water budget and have not been quantitatively evaluated for sediment transportation. In this study, we first estimated the water budget of the lake. Then the re-suspension by wind disturbance in the lake was estimated from the correlation with the wind speed based on laboratory experiments and field measurements. The outflow of the sediment estimated with these two models was compared with the sediment volume trapped in the upstream reservoirs that would have flowed into the lake if there had been no construction of the dams. Based on this, we evaluated whether the lake is currently erosive or cumulative. As a result, the estimated annual outflow of sediment to the sea was 4300 tons/year. It was estimated that the construction of the reservoirs upstream changed the trend of lakebed height from accumulation to erosion. [ABSTRACT FROM AUTHOR]

This study was undertaken with the primary objective of modeling grain velocity based on experimental data obtained under the controlled conditions of a laboratory using a rectangular hydraulic tilting channel. Soft computing approaches, i.e., support vector machine (SVM), artificial neural network (ANN), and multiple linear regression (MLR), were applied to simulate grain velocity using four input variables; shear velocity, exposed area to base area ratio (EATBAR), relative depth, and sediment particle weight. Quantitative performance evaluation of predicted values was performed with the help of three different standard statistical indices, such as the root mean square error (RMSE), Pearson's correlation coefficient (PCC), and Wilmot index (WI). The results during the testing phase revealed that the SVM model has RMSE (m/s), PCC, and WI values obtained as 0.1195, 0.8877, and 0.7243, respectively, providing more accurate predictions than the MLR and ANN models during the testing phase. [ABSTRACT FROM AUTHOR]

This study presents an integrated analysis of cohesive bank-collapsed material transportation in a high-curvature channel with a non-cohesive riverbed. A numerical model was established to simulate the erosion and transportation of collapsed materials in a 180° U-bend channel after verification. The novel aspect of this study is that the quantities of the collapsed materials that transformed into suspended and bed loads were comprehensively analyzed. The results show that finer collapsed sediments were only transformed into suspended loads after being eroded, while the coarser particles transformed into both suspended loads and bed loads. When the flow charge was 30 L/s, the quantity of collapsed materials (S1 and S2) that transported downstream was smaller, and coarser materials transformed into suspended loads with a ratio of 88.12–99.86% and bed loads with a ratio of 11.18–0.14%. When the flow charge was 55 L/s, due to the greater shear stress, the quantity of collapsed materials (S1 and S2) that transported downstream was greater, and the ratio ranged from 46.65% to 49.88% and from 50.12% to 53.35%, respectively. This research provides theoretical and practical benefits that reveal the mechanisms of channel bend evolution. [ABSTRACT FROM AUTHOR]

Dam construction often changes downstream fluvial processes by reducing sediment supply. Taking Tiaoguan reach and Laijiapu reach of the lower Jingjiang Reach downstream of the Three Gorges Project as examples, three-dimensional flow velocity, sediment, and bed elevation were observed in the two bends for investigating the impact of flow structure and sediment transport of different discharges on sharp bend morphology. Results indicated that the flow structure and sediment transport process in curved channels depended upon the flow stages, which affected the patterns of erosion and deposition along the point bars and concave banks. Flow separation and development of secondary flow were depended on the shapes of point bars and flow depths nearby, and the strength of secondary flow increased with flow discharge. The high flow discharges, which had high sediment carrying capacity and stream power, provided the main driving force for erosion on upstream point bar, thus the type and duration of floods were crucial factors in the morphological evolution of meandering bends. The reduction of sediment supply should be responsible for erosion on the point bars, causing the flow to migrate toward the convex banks. In meandering rivers with reduced sediment supply, retreats (push inward) of inner (convex) banks dominated advances (pull inward) of outer (concave) banks. In addition, the formation and development of concave-bank bars might relate particularly to meander curvature. This study is expected to constitute a reference for bank protection and river management in meandering bends downstream of reservoirs.

The Lancang-Mekong River is one of the largest transboundary river shared by China and Southeast Asian countries. In recent years, the sediment issue in this large river has received extensive attention due to nutrient-rich sediment decreasing which is critical to ecological health, aquatic habitats, shipping, coastal erosion and agricultural and fisheries production. A wide range of studies on sediment yield, transportation and trapped by reservoirs are summarized. The main controversial topics include where the most sediment comes from, how to explain the abnormal relationship among suspended sediment loads observed along the mainstream, and the quantification of effect of human activities on sediment load change. There are five main issues unsolved, including unreliable observed sediment data in Lower Mekong River, weak basis of total sediment load of 160 x 106 t/a, low spatiotemporal resolution in model simulation, insufficient study of the land use change impacts in recent decades and inadequate research on sediment except for suspended sediment. Several possible ways to overcome these difficulties are also discussed. [ABSTRACT FROM AUTHOR]

A typical diachronous breakup developed in the South China Sea (SCS); the breakup has been unequivocally identified, and gradually decreases in age from NE to SW. To illustrate the influence of a diachronous breakup on hydrocarbon accumulation, we used seismic profiles from CNOOC, and analysed crustal extension characteristics, sedimentary style and source rock accumulation. The main conclusions are as follows: (1) Because of the diachronous breakup in the SCS, various tectonic units developed in different positions on the northern continental margin with different degrees of extension. The Pearl River Mouth Basin (PRMB) is closer to the central sea basin of the SCS and has been affected by regional tension stress for a longer time. Tectonic units of proximal domain, necking zone, and distal margin types developed, and the crust structure thinned from the land towards the sea. The Qiongdongnan Basin (QB) is closer to the Southwest Sub-basin. There are symmetrical proximal domains on the southern and northern sides of the QB, with a necking zone in the central part. It presents as an abandoned passive continental margin. (2) The PRMB exhibited rifted cells first, followed by canyon type extensional faulting and horizontal axial transportation, and then by a longitudinal shelf-slope sedimentary style. But the QB has only rifted cells and canyon type faulting stages, no longitudinal shelf-slope sedimentary stage. The major source rocks in the northern SCS become younger from east to west, and the sedimentary facies change from lacustrine facies to marine-continental transitional facies. (3) The diachronous breakup process ultimately affecting oil and gas migration and accumulation process. The PRMB is dominated by deep-water shelf break accumulation with deep-water fan reservoir bodies. The QB is dominated by canyon type accumulation with channels. [ABSTRACT FROM AUTHOR]

Purpose: The trends in runoff and sediment transportation in typical Loess Plateau basins and the factors causing the changes need to be clarified. Materials and methods: In this study, the runoff and sediment transportation data from 1960 to 2016, from hydrological stations (Wenjiachuan, Baijiachuan, Ganguyi, and Zhuangtou) based in four typical basins, were analyzed systematically using linear regression, anomaly accumulation, the Mann–Kendall test, and double accumulation curve. The characteristics of the runoff and sediment transportation and their responses to climatic and anthropogenic activities were investigated using several hydrological analytical and statistical methods. Results and discussion: The results indicate that both runoff and sediment transportation in the four typical basins have decreased sharply from 1960 to 2016. Since the implementation of the Grain-for-Green Project in 1999, the reduction has been more marked, in particular the runoff and sediment discharge of the Kuye River (Wenjiachuan station). Compared with the period 1960–1999, the average annual runoff and sediment discharge in 2000–2016 had decreased by 76.72% and 94.50%, respectively. Apart from the Wuding River (Baijiachuan station), an abrupt change in runoff and sediment transportation in the basins occurred within 2–7 years of the implementation of the Grain-for-Green Project. Conclusions: In general, returning farmland to forests (grass) has had a more pronounced effect on the reduction of runoff and sediment in the more northerly Kuye River (Wenjiachuan station) and Wuding River (Baijiachuan station) basins, compared with the more southerly Yanhe River (Ganguyi station) and Beiluo River (Zhuangtou station) basins. [ABSTRACT FROM AUTHOR]

Abstract Assessing impacts of different factors on soil erosion is crucial for developing management of watershed resources. The present study aimed at determining the effect of rainfall intensity (RI) and slope steepness (SS) on sediments subjected to raindrop detachment (RD), transport by raindrop splash (ST), raindrop-induced flow transport (RIFT) and transport by flow (FT), using partial eta squared (ɳ p 2). Experiments were carried out on a plot (6 × 1 × 0.5 m) filled by silty loam soil and subjected to three RIs values of 30, 60 and 90 mm h−1 and three SS values of 5, 15 and 25% in three replicates. The total splash was influenced by RI with respect to ɳ p 2 and F-value of 0.29 and 14.68. It was found that the particle size <8 μm was significantly (P < 0.001) influenced by SS, while the impact of RI on the particle size >8 μm was more than that of SS. The effect of SS on sediment concentration and particles >63 μm and particle size 2–4, 4–8 and 8–16 μm of sediment reaching the outlet was more than that of RI with respect to ɳ p 2 of 0.93, 0.58, 0.51, 0.72 and 0.79. However, the clay content (particles <2 μm) with ɳ p 2 of 0.52 was influenced by RI more than by SS. The runoff rate was also significantly (P < 0.001) influenced by RI (ɳ p 2 = 0.64). RD-ST and RD-RIFT and RD-FT under different RI and SS combinations indicated that there was a significant difference (P < 0.001) in the transport of detached sediment of different size classes except for RI of 60 mm h−1 and 90 mm h−1 and SS of 25%. Highlights • Sediments of RD-ST, RD-RIFT and RD-FT were studied under laboratorial conditions. • Sediment size were quantified under various rain intensities and slope steepnesses. • Partial eta squared ascribed effects of rain intensity and slope on sediment size. • Size effects of rain intensity and slope steepness on sediments size were unlike. [ABSTRACT FROM AUTHOR]

To investigate the meso -mechanism of scouring process, a numerical model that couples the porous medium model, computational fluid dynamics and discrete elements method (PORO-CFD-DEM model) is established and validated. Two pipeline conditions, suspended and partially buried, are considered. The porous medium is used to replace most of the discrete elements, significantly reducing the computational requirements. Two particle generation methods, namely fictious grid method (FGM) and breath-first search method (BFM), are proposed, and three kinds of particle samples are generated with different gradations: Gaussian, gap and continuous. Detailed analyses of flow, fluid-particle interaction and sediment motion is conducted with an increasing inlet velocity. When the pipeline is suspended, the seepage flow is induced by the gap flow beneath the pipeline, with the pressure dropping along the seepage path. Around partially buried pipeline, the seepage flow is much weaker and the pressure concentration appears. The seepage force fluctuates, and the loose bed is disturbed, leading to randomly collapses. Different particle movement patterns, including the jumping, suspended transportation and the formation of sand slope, are captured during the simulations. It's confirmed that the PORO-CFD-DEM model can capture the meso -movement of the particles and provides insights into the theory of sediment transportation. [ABSTRACT FROM AUTHOR]

The grain size distribution (GSD) of sediment in comparison with the original soil GSD is discussed under different slopes (5, 15 and 25%) and rainfall intensities (30, 60 and 90 mm h–1with respective duration of 30, 15 and 10 min) but identical runoff (15 mm). The sediment quantification was carried out by raindrop-induced flow transport (RIFT) or/and transport by flow (FT) using a rainfall simulator and a 6 × 1 m2erosion plot and a silt loam. The results show a high degree of enrichment for size classes of 2–4 and 4–8 μm and a high degree of depletion for size classes of >63 μm under different slopes and rainfall intensities. In addition, the results show that the experimental enrichment ratio (ER) for particle size <16 μm under different slopes and rainfall intensities was greater than 1, while the ER for particle size >32 μm was less than 1. [ABSTRACT FROM AUTHOR]

On 26thDecember 2004, a strong Indian Ocean earthquake of moment magnitude 9 generated a deadly tsunami that hit the west coast of southern Thailand and many coastal nations of the Indian Ocean. Two tsunami-affected areas on the Thai Andaman coast (Ao Kheuy beach and Khuk Khak beach) were investigated. Multiple sediment layers in the tsunami deposits are identified and are analyzed. The sediment transportation patterns are also determined. Tsunami deposits consist of graded sand layers overlying the pre-existing soil. The particle size profile of the tsunami sediment and the plot of grain-size standard deviation with depth are used to identify major layers in tsunami deposit. There are three major sediment layers in the tsunami deposit in the study areas. They reflect three depositional sequences created by three tsunami run-ups. The mean grain-size of tsunami deposit and the results of sediment trend analysis show that the tsunami deposit is generally fining upwards and landwards. Each major sediment layer is created by sediments settled from suspension in a set of run-up and backwash. The percentage by weight of sediment settled from suspension during the backwash is small when it is compared to the percentage by weight of sediment settled from suspension during the run-up. The 1stdepositional sequence has higher quantity of coarse grain particles than the following depositional sequences. At a mild slope shore face, sediments are transported and deposited on land far from their origins. The number of major sediment layers in tsunami deposit can be used as the extending data for reconstructing individual tsunami run-up by using numerical and/or simple models.

Flood disaster has been one of the most frequent and devastating forms in middle Yellow River, China. Huge flood events transport sediments from upstream to downstream, and lead to changes of river morphology, such as river bed slope, channel roughness, and flood routing process. Flood disasters in the middle Yellow River were constantly caused by backwater effects due to multiple river stream confluence effects. The study aims to investigate confluent flood flow effects on flood routing processes, river morphology, and human activities based on a proposed flood flow model. The proposed model is constructed through coupling hydraulic equations, artificial intelligence neural network and probability theory. Flood frequency analysis is coupled with studies of hydrological routing processes that reduce the flood capacity of the rivers. Flood routing to the confluence were simulated using kinematic wave theory. Case studies have been carried out through field work and model simulation during the past years. Findings are achieved as followings. Firstly, flood frequency at the confluence implies that the confluent extreme flood occurs more frequently in the main streams than that in the tributaries due to influential intensity of East-Asian summer monsoon. Secondly, river morphology was altered partly due to complex flood routing processes in the middle Yellow River under the operation of Sanmenxia Reservoir. The alternated river channels changed the boundary conditions of flood routing, especially for backwater. Bed slopes have greater impacts on flood routing process than roughness does when there is larger flood flow. Finally, the evolution process of the sediment transportation is closely linked with the operations of the Sanmenxia Reservoir. [ABSTRACT FROM AUTHOR]

This research models soil erosion and sediment transportation in the Jialing River Basin based on the Revised Universal Soil Loss Equation (RUSLE) with Geographic Information System (GIS) technology. Studies have shown that, the improved method based on the RUSLE model was effective in calculating and predicting the annual sediment transport rate in Jialing River Basin in consideration of the hydrological conditions causing the annual variability of soil loss and the changes in the underlying surface resulting from land management activities. Comparing the observed and simulated sediment loads in the period of 1989 and 1998, the simulation values showed a consistent trend with the observed values, and the relative errors were controlled at 20% or less. This shows that the model can be used to identify hot-spot watersheds with different degree of sediment yield and help to make corresponding land use planning and soil and water conservation strategy, and thus help to reduce soil erosion in areas surrounding the Three Gorges Project and other reservoirs in other rivers. [ABSTRACT FROM AUTHOR]

Eroded sediment is an important feature of permanent gully's development; however, obtaining the specific characteristics of the sediment transport in the gully can be difficult. Thus, a composite fingerprinting technique, incorporating uncertainty analysis, has been employed to investigate the mean relative contribution of sediment sources in permanent gullies. In this study, 31 tracers were measured at 62 different sampling sites from three layers of a gully wall [surface layer (SL), sandy soil layer (SSL), and semi-weathering rock layer (SWL)] and 36 sediment samples from the slumping deposit and alluvial fan of the gullies. The sediment source tracing procedure was therefore used to assess the relative contribution of each source. The mean relative contribution from the SL to the sediment of the slumping deposit is higher in the active gully (G1), and is relatively lower in the potentially stable (G2) and stable gullies (G3); thus there was no obvious gully bank retreat in G2 and G3. In different places of the G1 alluvial fan, the mean relative contribution of the SL, SSL and SWL ranged from 9–11, 36–43 and 46–55%, respectively. However, the sediment contribution of the SL increased in G2 and G3 due to the changes in the erosion type. The mean relative contributions of the SL were 33 ± 5 (G2) and 30 ± 3% (G3). These findings have important implications for the establishment of a scientific basis for permanent gully sediment transport management and control policies. [ABSTRACT FROM AUTHOR]

Sandy desert landscape is a geological product of arid climate and abundant sand materials supply in natural conditions, therefore the formation of sandy desert is an ideal studying object for understanding the interaction between various stratigraphic/epigenetic spheres of the earth system. However, until now, the knowledge about the provenance and formation of these deserts in Xinjiang, Central Asia is diverse and inconsistent, a systematic review is necessary. Ancient aeolian sand sediments in the internal areas of these deserts and their twin dust deposits in the Cenozoic strata surrounding the Xinjiang deserts are direct and indirect clues reflecting the provenance of sand materials and the formation and evolution of deserts. Based on the geochemical, mineralogical and isotopic evidences of desert sands and relevant deposits in the peripheral regions, this paper reviews the research progress on the development of the sandy deserts in Xinjiang, Northwest China. Many proofs proposed that desert sands in Xinjiang were mainly sourced from the ancient pluvial, alluvial and fluvial sediments and were eventually achieved because of the local sand supply. It pointed out that the settings of tectonic structure in Xinjiang had made sediments both in the Tarim Basin and the Junggar Basin being influenced greatly by regional hydrological system and aeolian processes originated from the planetary wind system of westerly, the East Asian winter monsoon and the topographical mountain-valley winds. However, the directions of transportation paths are different between the hydrological dynamics and the aeolian dynamics, which are decided by the slantwise structures of the basins tectonics and the regional atmospheric circulation routes, respectively, and have determined anisotropies of the transport pathway of these sediments delivered by different agents. This results in a geological cycle of detrital sediment transportation in the two large basins and thus largely increases the degree of sediment mixing, alternation and recycle between younger and older sediment sources, as well as the complexity and diversity of sand provenances. [ABSTRACT FROM AUTHOR]

Questions A natural gravel-bed river is an important habitat for xerophytic plant species that prefer dry and periodically disturbed environments. However, human-impacted gravel bars covered with fine sandy sediments are often rapidly occupied by hygrophytic and mesophytic species, including weedy species, after a flush event. What is the mechanism by which these plant seeds are carried on gravel bars through a flush event? Can the seed traits of floating capability (buoyancy or settleability) and settling velocity in water explain seed accumulation in sandy sediments? Location The Tama River, central Japan. Methods Seed buoyancy/settleability and settling velocity in water were examined for 70 herbaceous species growing on newly deposited sediments of a river gravel bar. Settling velocities of sand particles of different sizes were estimated using theoretical formulas to compare with those of plant seeds. In addition, actual seed content of 36 samples of fresh sandy sediments were examined using a germination test to confirm coincident sedimentation of seeds and sand particles. Results Of the 70 species examined, only nine had apparently buoyant seeds and the remaining 61 species had non-buoyant seeds. We found that 53 (86.9%) of the 61 species having non-buoyant seeds had settling velocities comparable to those of very fine sand and fine sand particles, ranging from 0.062 to 0.25 mm in diameter. Furthermore, fresh sandy sediments deposited by a flush event contained many non-buoyant seeds of common species of above-ground vegetation. Both the germinated seedling number and species richness in the sediment samples showed positive correlation with the percentage weight of very fine sand and fine sand. Conclusions Seeds of most of the species that appeared after a flush event were considered carried by submerged dispersal through flowing water than through floating dispersal, because of their settleability. Many plant seeds could deposit together with fine sandy sediments as water velocity declined, since they had correspondent settling velocities. The main reason for rapid colonization by hygrophytic and mesophytic species was the settleability and settling velocity of the seeds. [ABSTRACT FROM AUTHOR]

Abstract: The contributions and relationships of erosion by splash and overland flow over a steep slope in a Japanese beech forest in plots with different percentages of ground cover were examined. Three erosion plots (2m wide×5m long) with average understory coverage of 1%, 45%, and 94% were installed. Sediment transported by rain splash and by overland flow was sampled separately. For the plots with sparse, moderate, and high understory coverage, the average proportions of splash soil to total soil erosion during the monitoring period were 16%, 32%, and 18%, respectively. A significant correlation between the amount of splash soil and precipitation was found in the plots with 1% and 45% understory coverage, whereas no statistical relationship was identified for the plot with high understory coverage. At the sparse ground cover plot showing the largest sediment movement, the contribution of splash transport decreased with increasing precipitation. The amount of sheetwash erosion was significantly correlated with the amount of splash soil under the condition of sparse ground cover. This relationship was more pronounced during high precipitation events and the rainy season. Splash contribution to the sediment transport was in the range of 0.8%–76.7%, 2.8%–81% and 2.1%–60.8% for plot with high, moderate and low ground cover, respectively. The sparse ground cover showed the largest variation of splash and sheetwash contribution in soil erosion. This variability was due to variation in ground cover and soil surface wetness condition which led to a variation of detachment and non-linear relationship of sheetwash splash. [Copyright &y& Elsevier]

Abstract: During the operations of purging and disposal of sediments of a reservoir it is necessary to know the values of turbidity in the river downstream in natural condition, in the absence of dams or river training works. The paper shows that under these conditions the ratio of the average values of sediment discharge to the annual maximum value of water discharge is a function of the average annual turbidity. Turbidity can be considered as representative synthetic index of the climatic conditions, the lithological features and the land cover of the basin, and the geometric characteristics of the river network. The proposed relationship of sediment discharge as a function of water discharge were validated on the basis of data collected from different Italian regions that have very different morphological, geo-lithological and rainfall features and that are characterised by a basin area changing between a few dozen and thousands of square kilometres. The results can be considered satisfying. [Copyright &y& Elsevier]

The genetic algorithm (GA) is a powerful method which can be used to solve search and optimization problems. A genetic algorithm with tournament selection, uniform crossover and uniform mutation is used to optimize sediment transport parameters in this study. Two important parameters of sediment transport, the critical shear stress for deposition and resuspension, are optimized by GA. The results show that GA is efficient and robust for optimizing parameters of our sediment transport simulation of Deep Bay. [ABSTRACT FROM AUTHOR]

The article presents a study on the estimation of the amount of suspended sediment in the Tigris River with the use of artificial neural networks (ANN) at the Diyarbakir measurement station in Turkey. The study made used of rainfall, discharge and temperature as independent variables in the models, while sediment as the dependent. There were 14 various models that were generated with the use of ANNs and Regression Analysis (RA). The results were compared with the observed data and it was concluded that ANNs give better result than RA due to their nonlinear modeling capability.

Abstract: Understanding of river systems that have experienced various forcing mechanisms such as climate, tectonics, sea level fluctuations and their linkages is a major concern for fluvial scientists. The 2525-km-long Ganga River derives its fluvial flux from northern part of the Indian subcontinent and drops in the Ganga–Brahmaputra delta and the Bengal fan regions. This paper presents a study of the Ganga River sediments for their textural properties, grainsize characteristics, and transportation dynamics. A suite of recently deposited sediments (189 bedload samples and 27 suspended load samples) of the river and its tributaries was collected from 63 locations. Dry and wet sieve methods of grainsize analysis were performed and Folk and Ward''s parameters were calculated. Transportation dynamics of the sediment load was assessed by means of channel hydrology, flow/sediment rating curves, bedform mechanics, grainsize images, and cumulative curves. Textural properties of the bedload sediments of the Ganga River tributaries originating from the Himalaya orogenic belt, the northern Indian craton and the Ganga alluvial plain regions are characterised by the predominance of fine to very fine sand, medium to fine sand, and very fine sand to clay, respectively. Downstream textural variations in the bedload and suspended load sediments of the Ganga River are, therefore, complex and are strongly influenced by lateral sediment inputs by the tributaries and channel slope. At the base of the Himalaya, a very sharp gravel–sand transition is present in which median grainsize of bedload sediments decreases from over −0.16 Φ to 2.46 Φ within a distance of 35 km. Downstream decline in mean grainsize of bedload sediments in the upper Ganga River within the alluvial plain can be expressed by an exponential formula as: mean grainsize (in Φ)=0.0024×Distance (in kilometres from the Himalayan front)+1.29. It is a result of selective transport phenomena rather than of abrasion, the condition attributed to channel competence with low gradient of 70 to 25 cm/km. Coarsening of the bedload sediments in the middle segment of the river develops due to the coarse bedload sediments (mean grainsize: 1.8–2.2 Φ) supply from the tributaries of the northern Indian craton region and increased unit stream power. The Ganga River sediments show a wide range of grainsize parameters [Bedload sediments: mean grainsize (1.5–3.8 Φ), standard deviation (0.3–0.7 Φ), skewness (−0.2–0.5), and kurtosis (0.8–2.4); suspended load sediments: mean grainsize (2.9–5.0 Φ), standard deviation (0.6–1.6 Φ), skewness (−0.6–0.4), and kurtosis (0.7–4.6)]. Mean grainsize of the bedload sediments is 2.6 Φ, which is 1.3 Φ units coarser than the suspended load sediments. The cumulative grainsize curves of the bedload sediments show a distinct “break” in slope, representing nearly 80% of the bedload sediment transported as graded suspension. During the peak monsoon discharge, most of the bedload sediments are transported as the discontinuous, fine sandy, graded suspension by the unidirectional unsteady shooting flow at a high transport rate (about 8×106 tons/d). A model of sedimentation transportation at river channel is proposed. The Ganga River mobilises a total of 729×106 tons of sediments annually through a narrow zone within its river valley. Under the present hydrogeological conditions, the river sedimentation is climatically controlled and is predicted to produce a 2000-km-long, 2- to 40-km-wide and 25- to 50-m-thick ribbon-shaped, well-sorted symmetrically skewed fine sand body. [Copyright &y& Elsevier]