Sediment Diameter Research Articles

Empirical Sediment Transport Models Based on Indoor Rainfall Simulator and Erosion Flume Experimental Data

AbstractLand degradation processes start with accelerated runoff and sediment delivery. In this study, rainfall‐runoff induced sediment transport is investigated using data from an indoor laboratory experimental setup consisting of a rainfall simulator and an erosion flume. The data are analysed to develop empirical models using sediment discharge, slope, flow discharge, rainfall intensity and sediment size. Fine and medium sands are considered as bare soil in experiments. Four rainfall intensities (45, 65, 85 and 105 mm h−1) are applied with combinations of lateral and longitudinal slopes of 5%, 10%, 15% and 20%. Eighty experiments are conducted. Flow is measured, and sediment within flow is separated and weighted. Experimental data are used for developing empirical models through multiple regression with parameters optimized by genetic algorithm. Results show that slope is the main contributing variable to the sediment transport over hillslopes. Accommodating variables among slope, rainfall intensity, flow discharge and median diameter of sediment as independent variables, one‐variable, two‐variable and four‐variable models are developed considering also that higher number of parameters increases the performance of the model with higher cost of parameterization. Copyright © 2016 John Wiley & Sons, Ltd.

Water erosion in surface soil conditions: runoff velocity, concentration and D50 index of sediments in runoff

Water erosion and contamination of water resources are influenced by concentration and diameter of sediments in runoff. This study aimed to quantify runoff velocity and concentration and the D50 index of sediments in runoff under different soil surface managements, in the following treatments: i) cropped systems: no-tilled soil covered by ryegrass (Lolium multiflorum Lam.) residue, with high soil cover and minimal roughness (HCR); no tilled soil covered by vetch (Vicia sativa L.) residue, with high soil cover and minimal roughness (HCV); chiseled soil after ryegrass crop removing the above-ground residues and keeping only the root system, with high roughness (HRR); chiseled soil after vetch crop removing the above-ground residues and keeping only the root system, with high roughness (HRV); ii) bare and chiseled soil, with high roughness (BHR). The research was conducted on a Humic Dystrupept under simulated rainfall. The design was completely randomized and each treatment was replicated twice. Eight rainfall events of controlled intensity (65 mm h−1) were applied to each treatment for 90 minutes. The D50 index, runoff velocity and sediment concentration were influenced by crop and soil management. Runoff velocity was more intensely reduced by cover crop residues than by surface roughness. Regardless of surface condition, the D50 index and concentration of sediment in runoff were lower under ryegrass than vetch crop. Runoff velocity and the D50 index were exponentially and inversely correlated with soil cover by residues and with surface roughness, while the D50 index was positively and exponentially correlated with runoff velocity.

Dyke overtopping: effects of shape and headwater elevation

ABSTRACTThis study deals with the erosion of granular laboratory dykes to allow for the prediction of the main dyke failure features, including the temporal advance of the maximum dyke height and the breach discharge. Two extreme scenarios are considered: (1) constant approach flow discharge; and (2) constant headwater elevation during the breach process, as the two extreme cases of prototype scenarios. Based on the previous research, the effects of three additional parameters, namely the up- and downstream dyke face slopes and the crest length, are considered by the so-called dyke shape parameter. Its effect is included in the governing dyke breach equations so that all relevant variables vary only as a function of discharge scenario, original dyke height, and sediment diameter. The breach process is described with typical images and plots, to highlight the various effects. The results allow for an estimate of the dyke breach characteristics based on Froude similitude.

Effectiveness of Sediment Flushing by Using By-Pass Flush Canal

The objective of this study was to analyze the effectiveness of sediment flushing system of BY PASS channel with 1 door, 2 door and 3 door at a floodway. To determine which was the most effective, empirical model of effectiveness of each channel of sediment flushing were built. The object model of this study was the Floodway Sedayu Lawas, located in Lamongan, East Java Province. This study uses Hydraulic Physical Model Test. Built and test the model conductedin the Laboratory of River, in Surakarta, Cental of Java. The variables of this study were sediment weight (W), water depth(H), sediment mass density (ρs), sediment diameter (ds), waterflow rate (Q), and floodway wide (Bo)

Relationship Between Estuarine Shellfish Fauna and Physical Environmental Characteristics for Estuary Conservation in Kyushu, Japan

The establishment of a conservation strategy or restoration goal for river estuaries requires knowledge of potential biota or possible habitat characteristics. In this study, we investigated the relationship between estuarine fauna and macro scale physical indicators on Kyushu Island, Japan to provide basic information for estuarine conservation. As a result of the classification of shellfish fauna by similarity, the Kyushu region was divided into three groups, namely, 1) southern Kyushu with high wave exposure, long fetch, and low tidal variation; 2) the Ariake and Yatsushiro seas with low wave exposure, short fetch, and high tidal variation; and 3) northern Kyushu with an intermediate fetch and tidal variation. In addition, a number of sites, such as Nakatsu Port, Sone tideland, and the Honmyou River, were classified into geographically different groups. This is because the physical characteristics of these sites were similar to classified groups or shellfish fauna were significantly altered by artificial impacts. As a result of discriminant analysis, the discrimination hit rate of species inhabiting the inner bay or tidal flat was high, whereas that for species using a wide variety of bottom sediment environment was low. To improve the accuracy of the discriminant model, it is necessary to collect more detailed physical information, such as habitat type, salinity concentration, or grain diameter of bottom sediment. To establish a conservation or restoration strategy, there is a need for classifying taxonomic groups or physical characteristics.

Representative sediment sizes in predicting the bed-material load for nonuniform sediments

This paper evaluates the applicability of representative sediment size in terms of median grain size and the effective sediment sizes for the transport of non-uniform natural sediment mixtures. Natural sediment from the Krasak River, Yogjakarta was used. Bed samples were collected from three different river sections, i.e. upstream (U), midstream (M) and downstream (D). The median diameters, d50 and sediment geometric standard deviation, σg for sections U,M and D were 1.63mm, 0.91mm and 0.69mm, and 4.8, 2.3 and 1.5 respectively. Particular attention was paid to the effect of varying representative sediment sizes on the threshold sediment motion, where four threshold equations were employed. The threshold value varies when σg=4.8 and has little variation for sediment mixtures with σg<2.4. Analysis is extended to prediction of bedload transport using eight selected formulae which account for both with and without the threshold criteria of sediment motion. To account for the non-uniformity of the bed materials, a comparison between the calculated bedload discharge using d50 was made with the bedload prediction when a representative sediment diameters were used. Analysis shows that an improvement of the statistical analysis was only observed for predictions calculated using Brownlie (1981) and Camenen and Larson (2005) expressions when effective sediment sizes were employed for non-uniform sediment mixtures. Employing the effective sediment sizes de or dem to calculate the bedload discharge does not necessarily improve the bedload prediction and the use of d50 is seen as sufficient.

Scaling and Self-Similarity of One-Dimensional Unsteady Suspended Sediment Transport with Emphasis on Unscaled Sediment Material Properties

AbstractCurrent methods utilized in scaling sediment transport in unsteady open-channel flow result in a number of model and scale effects, decreasing the accuracy and applicability of scale models. Identifying the conditions under which the governing equations of sediment transport are self-similar, and require no sediment diameter or density scaling, can reduce scale effects and increase model applicability. Conditions for self-similarity of one-dimensional unsteady suspended sediment transport are identified by applying the one-parameter Lie group of point scaling transformations, both for the general case and with unscaled sediment diameters. Under the scaling ratio relations found when holding sediment diameter to be unscaled, sediment diameter, density, critical and total shear, porosity, kinematic viscosity, and particle Reynolds number are all unscaled. It is shown that under Lie group scaling, the unsteady one-dimensional suspended sediment transport process as an initial-boundary value problem i...

Fluvial River Regime in Disturbed River Systems: A Case Study of Evolution of the Middle Yangtze River in Post-TGD (Three Gorges Dam), China

The fluvial river is a kind of open system that can interact with its outside environments and give response to disturbance from outside on the earth. It can adjust itself to the disturbances outside the system and reflects new characteristics in the process of reaching a new equilibrium. The TGD (Three Gorges Dam) constructed at the Yangtze River Upstream was set up to operate in 2003. And it has changed the boundary conditions of the downstream reaches and has broken the long term equilibrium of the Yangtze River system. The reaches alter the river regime to response the disturbance from the TGD. In this paper, the case study Shashi Reach is selected to analyze the variations of the river regime in a river system. The discharge is becoming smoother without large peak or lower discharge for the regulation of the reservoir. The sediment diameter becomes coarser downstream of the TGD and the sediment transport rate decreases as the sediment concentration becomes lower, in spite of the sediment erosion along the reach downstream. The thalweg moves in plane dramatically to adjust itself to reach a new equilibrium. And the topography changes a lot since there are different sediment and flow conditions. The disturbed river system is in the process of reaching a new equilibrium.

Numerical Analysis of Cone-Jet Based on EHD Micro-Jet Technology

EHD micro-jet can deposit rule and functional patterns in a direct, continuous and controllable manner, and has the advantages of good compatibility, high resolution and simple structure, thus becoming a cost-effective and high-efficiency technology. Through numerical method, obtain the three dimensional model of cone-jet and emphasize the correlation of sediment diameter and PEO concentration. The theoretical graphics agree well with the experimental data, which can explain and provide some theoretical basis for the experiments.

Transport and emplacement mechanisms of channelised long-runout debris avalanches, Ruapehu volcano, New Zealand

The steep flanks of composite volcanoes are prone to collapse, producing debris avalanches that completely reshape the landscape. This study describes new insights into the runout of large debris avalanches enhanced by topography, using the example of six debris avalanche deposits from Mount Ruapehu, New Zealand. Individual large flank collapses (>1 km3) produced all of these units, with four not previously recognised. Five major valleys within the highly dissected landscape surrounding Mount Ruapehu channelled the debris avalanches into deep gorges (≥15 m) and resulted in extremely long debris avalanche runouts of up to 80 km from source. Classical sedimentary features of debris avalanche deposits preserved in these units include the following: very poor sorting with a clay-sand matrix hosting large subrounded boulders up to 5 m in diameter, jigsaw-fractured clasts, deformed clasts and numerous rip-up clasts of late-Pliocene marine sediments. The unusually long runouts led to unique features in distal deposits, including a pervasive and consolidated interclast matrix, and common rip-up clasts of Tertiary mudstone, as well as fluvial gravels and boulders. The great travel distances can be explained by the debris avalanches entering deep confined channels (≥15 m), where friction was minimised by a reduced basal contact area along with loading of water-saturated substrates which formed a basal lubrication zone for the overlying flowing mass. Extremely long-runout debris avalanches are most likely to occur in settings where initially partly saturated collapsing masses move down deep valleys and become thoroughly liquified at their base. This happens when pore water is available within the base of the flowing mass or in the sediments immediately below it. Based on their H/L ratio, confined volcanic debris avalanches are two to three times longer than unconfined, spreading flows of similar volume. The hybrid qualities of the deposits, which have some similarities to those of debris flows, are important to recognise when evaluating mass flow hazards at stratovolcanoes.

우수관로 경사 조정에 따른 토사 퇴적 특성 분석

관거 내에 퇴적된 토사로 인한 통수능 저감은 도심지 국지성 집중호우에 대한 내수침수의 위험성을 증가시키게 되므로 이에 대한 고려가 관거의 설계 및 유지관리상에서 이루어져야 한다. 그러나 현행 국내 우수관거 설계에 있어서 관거 내의 토사 퇴적에 대한 고려 및 이에 대한 연구는 매우 미흡한 상태이며, 따라서 이에 대한 향후 연구 및 설계기준 마련이 시급한 실정이다. 본 연구에서는 우수관거에서의 토사 퇴적을 저감하고 원활한 통수능 확보를 위하여 설계시 고려되어야 할 사항들에 대하여 검토해보았다. 이를 위해 가상의 관망에 대한 경사 조정을 통하여 토사 입경별 관거 내 퇴적 양상을 분석하였다. 또한 실제 도심지 우수관망에서의 관거 설계 변경에 따른 토사 퇴적 양상을 분석하기 위하여, 부산시 부전천 유역에 대하여 현재의 우수관로를 임의로 경사를 조정함으로써 관거 내 토사의 퇴적량을 저감시키고자 하였다. 분석 결과 부전천 유역의 우수관로에 대한 구간 경사 조정을 통하여 관로 내 토사의 퇴적 총량이 약 30%이상 감소될 수 있는 것으로 나타났다. 다만 퇴사량 총량과는 별도로 개개 관거의 토사 퇴적 깊이가 다양한 증감 양상을 나타냄으로 관로 전체의 안정성 측면에서는 토사의 퇴적량 및 퇴적 깊이를 동시에 고려할 수 있는 신뢰도 함수의 산정과 이에 따른 관로 설계가 중요한 것으로 나타났다. Reduction of discharge capacity due to sedimentation in sewer increase danger of the inundation risk because of occurrence of frequent localized heavy rainfall, we need to find the fundamental solution for sewer design and maintenance. However, internal researches considering sedimentation in sewer designs are very insufficient, should be urgently required by considering the characteristics about future research and design standards. In this study, examines the design concept for discharge capacity and reduction of sedimentation in sewer networks. The virtual sewer networks are designed to analysis and distribute the sedimentation of depositional patterns in the sewer conduits, while considering the sedimentation diameter, in order to reduce the inundation risk. Accordingly, to analyze detailed changes in conduit designs in urban sewer networks, tried to reduction of sedimentation in sewer networks using modified pipe slope in Bujeon stream catchment, Busan. The various sewer designs were applied to Bujeon stream catchment and then, the most effective reduction of sedimentation volume over 30%. Just, total sedimentation depth separately intended the variation cases contrary to total sedimentation volume, we need to consider about entirely adequate aspect of related to design safety. So, including both the volume and the depth consideration through estimating the reliability of sewer network systems.

A surface roughness model for predicting alluvial cover and bed load transport rate in bedrock channels

AbstractPartial alluvial cover in bedrock channels influences downcutting rates and mountain river morphodynamics. Flume experiments have demonstrated that a wide range of stable cover fractions are possible for a given ratio of sediment supply to transport capacity. Existing cover models impose different unique relationships between cover fraction and reach‐scale transport variables (e.g., slope, discharge, sediment supply, and grain size). Individually, these models cannot predict the range of cover behaviors observed experimentally, suggesting that additional variables may be important. I propose a 1‐D model in which bedrock surface roughness is a control on partial alluvial cover. In the model, surface roughness affects both shear stresses and thresholds of grain motion and therefore sediment transport capacity. The roughness of the combined bedrock‐alluvial bed surface varies with the cover fraction. Model trends are reasonably consistent with previous experiments over ranges of roughness, slope, and shear stress. When bedrock roughness is much greater than grain size, cover increases approximately linearly with the ratio of sediment supply to transport capacity. When bedrock roughness is much less than the sediment diameter, the model tends to predict abrupt shifts between complete bedrock exposure and alluvial cover. This runaway alluviation occurs for model solutions that are unstable to perturbations in supply, which is the case when transport capacity decreases as alluvial cover increases. In addition, a model variant in which sediment supply is controlled by the amount of sediment on the bed suggests that a linear cover relation may be sufficient for modeling sediment flux‐dependent erosion at landscape scales.

The Development of the Near-Bed Sediment Sampler

The determination of sediment concentration of near bed, because of high sediment concentration and disruption of measuring device, is a difficult point in field survey. A water body sampler is developed to get samples of sand-containing water body close to the bed. Then, the basic features like sediment concentration at different level and sediment diameter can be determined. Combined with flow rate measurement, the near-bed sediment runoff rate can also be estimated.

Prediction of berm geometry using a set of laboratory tests combined with teaching–learning-based optimization and artificial bee colony algorithms

Understanding sediment movement in coastal areas is crucial in planning the stability of coastal structures, the recovery of coastal areas, and the formation of new coast. Accretion or erosion profiles form as a result of sediment movement. The characteristics of these profiles depend on the bed slope, wave conditions, and sediment properties. Here, experimental studies were performed in a wave flume with regular waves, considering different values for the wave height (H0), wave period (T), bed slope (m), and mean sediment diameter (d50). Accretion profiles developed in these experiments, and the geometric parameters of the resulting berms were determined. Teaching–learning-based optimization (TLBO) and artificial bee colony (ABC) algorithms were applied to regression functions of the data from the physical model. Dimensional and dimensionless equations were found for each parameter. These equations were compared to data from the physical model, to determine the best equation for each parameter and to evaluate the performances of the TLBO and ABC algorithms in the estimation of the berm parameters. Compared to the ABC algorithm, the TLBO algorithm provided better accuracy in estimating the berm parameters. Overall, the equations successfully determined the berm parameters.

Prediction of cross-shore sandbar volumes using neural network approach

Correct estimation of bar volumes, wave height, wave period and median sediment diameter is crucial for the designing of coastal structures and water quality problem. In this study, bar volumes caused by cross-shore sediment transport were investigated using a physical model and obtained 64 experimental data considering the wave steepness (H0/L0) and period (T), the bed slope (m) and the sediment diameter (d50). Artificial neural network (ANN) and multi-linear regression (MLR) are used for predicting the bar volumes. A multi layer perceptron is used as the ANN structure. The results show that the ANN model estimates are much closer to the experimental data than the MLR model estimates.

The effect of environmental factors on spatial variability in land use change in the high-sediment region of China’s Loess Plateau

In areas with topographic heterogeneity, land use change is spatially variable and influenced by climate, soil properties, and topography. To better understand this variability in the high-sediment region of the Loess Plateau in which soil loss is most severe and sediment diameter is larger than in other regions of the plateau, this study builds some indicators to identify the characteristics of land use change and then analyze the spatial variability as it is affected by climate, soil property, and topography. We build two indicators, a land use change intensity index and a vegetation change index, to characterize the intensity of land use change, and the degree of vegetation restoration, respectively. Based on a subsection mean method, the two indicators are then used to assess the spatial variability of land use change affected by climatic, edaphic, and topographic elements. The results indicate that: 1) Land use changed significantly in the period 1998–2010. The total area experiencing land use change was 42,302 km2, accounting for 22.57%of the study area. High-coverage grassland, other woodland, and forest increased significantly, while low-coverage grassland and farmland decreased in 2010 compared with 1998. 2) Land use change occurred primarily west of the Yellow River, between 35 and 38 degrees north latitude. The four transformation types, including (a) low-coverage grassland to medium-coverage grassland, (b) medium-coverage grassland to high-coverage grassland, (c) farmland to other woodland, and (d) farmland to medium-coverage grassland, were the primary types of land use change, together constituting 60% of the area experiencing land use change. 3) The spatial variability of land use change was significantly affected by properties of dryness/wetness, soil conditions and slope gradient. In general, land use changed dramatically in semi-arid regions, remained relatively stable in arid regions, changed significantly in clay-rich soil, remained relatively stable in clay-poor soil, changed dramatically in steeper slopes, and remained relatively stable in tablelands and low-lying regions. The increase in vegetation coincided with increasing changes in land use for each physical element. These findings allow for an evaluation of the effect of the Grain to Green Program, and are applicable to the design of soil and water conservation projects on the Loess Plateau of China.

Upstream sediment transport of the gate across a channel

The results of an experimental investigation of the time variation of scour width, upstream scour length and scour depth and the flow characteristics of the quasi-equilibrium state of scour a non-cohesive bed upstream of gate openings due to hydraulic differences and gate opening sizes are presented. Experiments were carried out with non-cohesive sediments for various gate openings, sediment diameter, and hydraulic differences including upstream depth. Attempts have been made to explain the main parameters affecting upstream sediment transport. The scour profiles at different times follow a particular geometrical similarity and can be expressed by a polynomial using relevant parameters. The characteristic parameters affecting the time variation of scour width, upstream scour length and scour depth are identified based on physical reasoning and a dimensional analysis. Equations for time variation of maximum scour width, upstream scour length, and scour depth are obtained empirically. A regression analysis between the measured value in a hydraulic laboratory and the predicted value in a prediction model of upstream sediment transport matched well with the determinant coefficients (r2) which were 0.84 for scour width, 0.89 for upstream scour length, and 0.70 for scour depth.

Mechanism of Sediment Flocs Formation in the Three Gorges Reservoir

Settling velocity of sediment increases if flocculating occurred, and this enlarges deposition in reservoirs. According to water environmental factors in the Three Gorges reservoir, potential energy and forces between particles are evaluated based on DLVO theory. The critical water dynamics conditions were obtained by comparing extremum in synthetic potential curve and kinetic energy caused by relative velocity between particles. It is found that sediment flocculating is apt to happen when water level is high according to flow dynamics in the Three Gorges reservoir. The flocs are relatively loose and which is prone to be broken by water shear force. So the settling velocity of the flocculation is limited and the critical diameter of sediment is 0.019mm under which the sediments are affected by flocculating, and the settling velocity should be revised according to the limited settling velocity of flocculation when sediments are smaller than the critical diameter.

Live-bed local scour around vertical-wall abutments

Local scour experiments were performed with four different uniform cohesionless sediment diameters d50 = 0.26, 0.42, 1.06, and 1.92 mm and five vertical-wall abutments with projected lengths l = 0.04, 0.06, 0.08, 0.10, and 0.12 m perpendicular to the flow. These tests were conducted at different flow velocity (V) varying from 0.71 to 5 times of the critical velocity (Vc). The plotting of scour depths dse vs. V/Vc shows that the scour depths increase up to the threshold value of flow (V/Vc = 1) and after that it reduces and again increases to attain the live-bed maximum in the flow range V/Vc = 3–5. It is observed that the scour depth increases with the increase of sediment sizes and abutment lengths. Further, the scour depth decreases with the increases of nonuniformity under all flow conditions. A design equation is proposed based on the present experimental data and existing live-bed scour data. The measured values of scour depth are compared with the calculated values using proposed equation and also with three different live-bed local scour equations for the conditions of the tests.

Overtopping dike-breach: effect of grain size distribution

ABSTRACTA series of plane dike overtopping laboratory tests is reported, in which the effect of sediment mixture on the breach process is investigated. Three different sediment mixtures were tested, in addition to the reference dike consisting of uniform non-cohesive sediment. No sealing elements or surface protection were applied. The adopted constant reservoir inflow led to a falling reservoir scenario. The experiments demonstrate that the grain size distribution has a small effect on the overall breach process within the given test range, as the hydraulic conditions during the dike breach are much above the sediment entrainment condition. No increased erosion resistance was observed for the sediment mixtures. Therefore, the mean sediment diameter adequately describes the non-cohesive material characteristics and general dike-breach features in laboratory scale can be investigated using uniform material. This finding is significant both for laboratory experimentation and for prototype dike construction.