Sand Bed Research Articles

Impacts on alternate bar geometry and dynamics in a trained sand bed river

This study investigates the occurrence and dynamics of single row alternate bars forming in a particular reach of the sand bed Elbe River in Germany. Although the formation and dynamics of alternate bars have been intensively investigated in the literature, there exists only a limited number of studies focusing on the characteristics of alternate bars forming under complex field conditions. This is particular the case for bars forming in trained sand bed rivers, as most previous field studies have focused on gravel bed rivers. Moreover, little is known on the impact of river training structures on bar characteristics in anthropogenic rivers. To close this gap, we present a comprehensive bed elevation data set that was collected over a period of 10 years within a 30 km long reach of the lower Elbe River in Germany by the Federal Waterways and Shipping Administration (WSV). The reach is characterized by a sand bed, has curved as well as straight parts, and exhibits a section that is less trained by groins than the neighboring sections. For our analyses, we propose a novel approach to estimate bar characteristics based on statistically derived geometrical parameters. The outcomes of the approach are used to show that bars in Elbe River belong to the free bar type and that their origin of formation and characteristics depend on hydrological and geometrical boundary conditions. The results reveal that the active width of the river bed, defined as the distance between the groin heads, is a crucial parameter for the occurrence of alternate in the reach. We further highlight the impact of river bends on bar characteristics, as bars in the outer bend were longer and higher than their inner bend counterparts. Finally, we show that simple predictors for bar formation can be successfully applied to predict bar formation in sand bed rivers but that care needs to be taken when applying such approaches to more complex boundary conditions.

Seismic driven reservoir classification using advanced machine learning algorithms: A case study from the Lower Ranikot/Khadro sandstone gas reservoir, Kirthar Fold Belt, Lower Indus Basin, Pakistan

Reservoir characterization of thin sand bed reservoirs has been a challenge for petroleum explorers across the globe. In this study, we have studied the heterogeneous Paleocene sandstone gas reservoir of Lower Ranikot/Khadro, Kirthar Fold Belt, Lower Indus Basin, Pakistan. The studied reservoir is par below seismic resolution, with an average thickness that varies from 4 to 7 m at places and has provided a good amount of prosecution in some producing wells. The solution to the above challenges has been put forth where an integrated approach of seismic attributes, petrophysical properties, well logs, and facies data sets are combined with advanced machine learning algorithms to get better resolution for the studied thin-bedded sandstone resource. In addition, the thin heterogeneous sands of the Ranikot/Khadro Formation were characterized by predicting the elastic properties of the reservoir and classifying the facies distribution of hydrocarbon-bearing sands within the Zamzama Gas Field. Several machine learning (ML) algorithms were chosen and implemented on pre-stack seismic data from seven wells, two of which were produced from the Paleocene reservoir. The Gradient Boosting Regressor (GBR) produced promising results with the demarcation of thin sands with high accuracy levels. Based on a successful petro-elastic relationship, thin gas sands were highlighted. The low VCL of 30% and Sw of 45% cut-off reflect gas sands with P-impedances of 7500–9500 m/s × g/cc and a Vp/Vs ratio of 1.4–1.6 as decisive ML characteristics. Based on the applied workflow aided by ML, three reservoir units have been assigned for the Paleocene hydrocarbon-bearing sands, and gas sand probability distribution maps have been developed for each reservoir unit. Aligning the seismic inversion technique with machine learning advanced algorithms not only speeds up the prediction of elastic properties for facies classification but also increases accuracy to over 90% while drastically reducing uncertainty and associated costs in the process. Advanced machine learning algorithms have allowed us to cater to thin sand beds by eliminating the need for injecting frequencies. Instead, it recognizes features from the well data, trains itself, and predicts the corresponding features on the seismic trace, thus effectively allowing us to characterize the beds that are below seismic resolution in any given complex geology. The generated probability distribution maps of the three recognized thin-bedded sand units can be the basis for petroleum exploration and development in the study area. The discussed technique is successfully applied to complex folds and thrust belts, and hence can be implemented successfully in other heterogeneous thin-bed reservoirs for the successful classification of hydrocarbon-bearing sand distribution. It would optimize the results in a short period of time and with fewer economics.

Semi-saturated Sand and Pebble Beds Use in Secondary Treatment of Urban Wastewater

Semi-saturated Sand and Pebble Beds Use in Secondary Treatment of Urban Wastewater

Performance of iron sand as an oxygen carrier at high reduction degrees and its potential use for chemical looping gasification

Iron sand as an industrial by-product has a reasonable iron content (35 wt% Fe) and low economical cost. The reactivity of iron sand as an oxygen carrier was examined in a bubbling fluidized bed reactor using both gaseous and solid fuels at 850–975 °C. Pre-reductions of iron sand were performed prior to fuel conversion to adapt the less-oxygen-requiring environment in chemical looping gasification (CLG). Based on the investigations using CO and CH4, iron sand has an oxygen transfer capacity of around 1 wt%, which is lower than that of ilmenite. The conversion of pine forest residue char to CO and H2 was higher when using iron sand compared to ilmenite. Depending on the mass conversion degree of iron sand, the activation energy of pine forest residue char conversion using iron sand was between 187 and 234 kJ/mol, which is slightly lower than that of ilmenite. Neither agglomeration nor defluidization of an iron sand bed occurred even at high reduction degrees. These suggests that iron sand can be utilized as an oxygen carrier in CLG. Furthermore, this study presents novel findings in the crystalline phase transformation of iron sand at various degrees of oxidation, altogether with relevant thermodynamic stable phases.

Land Use and Land Cover Change Monitoring and Prediction of a UNESCO World Heritage Site: Kaziranga Eco-Sensitive Zone Using Cellular Automata-Markov Model

The Kaziranga Eco-Sensitive Zone is located on the edge of the Eastern Himalayan biodiversity hotspot region. In 1985, the Kaziranga National Park (KNP) was declared a World Heritage Site by UNESCO. Nowadays, anthropogenic interference has created a significant negative impact on this national park. As a result, the area under natural habitat is gradually decreasing. The current study attempted to analyze the land use land cover (LULC) change in the Kaziranga Eco-Sensitive Zone using remote sensing data with CA-Markov models. Satellite remote sensing and the geographic information system (GIS) are widely used for monitoring, mapping, and change detection of LULC change dynamics. The changing rate was assessed using thirty years (1990–2020) of Landsat data. The study analyses the significant change in LULC, with the decrease in the waterbody, grassland and agricultural land, and the increase of sand or dry river beds, forest, and built-up areas. Between 1990 and 2020, waterbody, grassland, and agricultural land decreased by 18.4, 9.96, and 64.88%, respectively, while sand or dry river beds, forest, and built-up areas increased by 103.72, 6.96, and 89.03%, respectively. The result shows that the area covered with waterbodies, grassland, and agricultural land is mostly converted into built-up areas and sand or dry river bed areas. According to this study, by 2050, waterbodies, sand or dry river beds, and forests will decrease by 3.67, 3.91, and 7.11%, respectively; while grassland and agriculture will increase by up to 16.67% and 0.37%, respectively. The built-up areas are expected to slightly decrease during this period (up to 2.4%). The outcome of this study is expected to be useful for the long-term management of the Kaziranga Eco-Sensitive Zone.

Performance enhancement of stepped solar still via different sand beds, cooling coil and reflectors

Performance enhancement of stepped solar still via different sand beds, cooling coil and reflectors

Simulation of Seabed Erosion Produced by an Inclined Jet

Water jets are widely used in seabed scouring and desilting applications. In the present work, dedicated tests have been conducted using a jet scour model test platform and sand beds containing grains with different sizes. The FLOW-3D simulation software has also been used to tackle the problem form a numerical point of view. The boundary conditions of the simulation have been optimized to reduce the gap between the numerical results and the outcomes of the experimental tests. Scour area calculation has been based on a RNG k-ε Turbulence model. Moreover, the FAVOR (Fractional Area Volume Obstacle Representation) technology has been selected for grid division to make the simulation results more accurate. Jet scours with inclination angles of 10–20° have been simulated. It has been found that jet scouring is greatly affected by the environmental water flow, that is, water flow can weaken the scouring capacity of the jets.

Processes for the Clarification of the Crude Oil of Baobab Seeds Extracted by Pressing on Activated Carbon Elaborated from the Capsules of the Fruit (<i>Adansonia digitata</i> L.)

The baobab, Adansonia digitata L. plays an important role in the economy of local populations. The oil from the seeds of the baobab fruit is nowadays highly prized because of its numerous cosmetic and therapeutic applications and its composition of unsaturated fatty acids, sterols and tocopherols. However, unlike refined oils, locally extracted baobab oil has not undergone purification operations to ensure its quality. Only a filtration on special cloths is carried out after decantation. Indeed, the oil obtained after pressing is cloudy because of the presence of various impurities. It therefore requires treatment operations to make it more attractive and of higher quality. Therefore, in order to provide innovative solutions to local companies to improve the quality of vegetable oils, a study of clarification (treatment) of crude oil is necessary. An experimental device has been developed in the laboratory. It includes a glass column and a filter bed of dune sand and activated carbon. This study has shown the efficiency of the experimental device. Indeed, the activated carbon, thanks to its adsorbing power, has allowed a significant decrease in turbidity at the 5% threshold, from 14.61 NTU for the raw oil to 0.08 NTU for the oil filtered on 3% carbon and 0.033 NTU for the oil filtered on 5% carbon. That is to say an abatement higher than 95%. This decrease in turbidity could be correlated with the decrease in brown index from 187.39a for the initial crude oil to 128.53d for the oil treated with 3% activated carbon versus 187.59a for the oil filtered on cloths. The lowest brown index was observed with the filtration using 5% activated carbon (35.99b). Thus, for the yellowness index, only the filtration on 5% charcoal allowed to obtain a significant decrease in yellowness. The yellowing index of the oil with 5% was 44.67b against 79.04a for the oil filtered with 3% activated carbon, 86.33a for the crude oil and 86.46a for the oil filtered on cloths. Finally, the oil sample treated with 5% activated carbon had the clearest clarity than the other samples with a clarity (L) equal to 97.98c against 95.63d for the oil treated with 3% carbon and 94.99b for the oil filtered on filter cloths. According to the results obtained, the experimental device made it possible to obtain a clearer baobab oil with a low brown index, thus improving the sensory quality of the oil.

Impact force of post-fire debris flows over erodible beds

After wildfire events, water repellent soil is often found in the subsurface layer of channel bed in the burnt area. Debris flows generated from burnt basins and ensuing entrainment of the channel bed pose imminent threat to infrastructure and human lives. However, the fundamental interaction mechanisms of debris flow overriding water repellent bed and resulting impact force on debris-resisting barriers have yet to be elucidated. In this study, physical flume experiments are conducted to simulate post-fire debris flows overriding and entraining a sand bed with varied wettability. Compared to a wettable bed, water repellent sediment exhibits a tremendous increase in the erosion depth and subsequent impact force on the barrier. The test results demonstrate that debris flows overriding water repellent sediment can be particularly hazardous and the effects of water repellency need to be captured by the design criteria of debris resisting barriers in burnt basins.

Scour depth development at piles of different height under the action of cyclic (tidal) flow

The impact of cyclic (tidal) flow on scour at cylindrical monopiles in the live-bed regime has been examined on the basis of results from mobile sand bed flume experiments. Four tests were conducted with four 0.114 m diameter piles of differing stickup height placed across the 4 m wide test section of the Fast Flow Facility. The tidal tests Tide01, Tide02 and Tide03 had the same peak current speed in forward and reverse direction with different cycle periods to examine the role of cycle length on scour. The period in Tide01 was approximately halved in Tide02 and doubled in Tide03. A unidirectional test Uni01 was run for comparative purposes. The results have shown how the cycle length adopted in testing has a key controlling effect on the scour achieved in a fixed number of cycles. The scour data measured on two sides of the piles at 1 Hz are plotted both in time-series format and pairwise to illustrate the cyclic nature of the scour development and recycling of sediment within the scour hole. The effective work method of Link et al. (2016) provides a good correlation for the dimensionless scour depth. The cyclic behaviour of the scour difference across the pile diameter has been analysed in terms of a basal slope and the magnitude of the scour depth, akin to geotechnical testing of monopile response to cyclic loads. Comparison with field measurements of scour shows that the cyclic tests can achieve non-dimensional scour depths found in the field. A progressive reduction in the slope angle is demonstrated for increasing number of cycles but further investigation of the different angle observed in field and laboratory is required. Finally the effect of pile stickup height is evaluated using both published and the current data, and a modified value of the Sumer and Fredsøe coefficient is proposed for undirectional and tidal scour. • Experimental analysis of tidal (cyclic) flow impact on scour development at piles. • Updated coefficient in prediction equation for scour at truncated piles in unidirectional and tidal currents. • Presentation of results in terms of cyclic behaviour of scour magnitude and basal slope in the scour pit.

Experimental Study of Rice Husk Fluidization Without a Sand Bed Material on a Bubbling Fluidized Bed Gasifier

This study aimed to determine the effect of rice husk fluidization and variation in the equivalence ratio of bubbling fluidized bed gasifiers without sand bed materials. It also aimed to improve the fluidization quality by reducing the diameter of rice husks. Therefore, the bulk density increases, whereas voidage decreases, both of which are the main parameters for improving the quality of fluidization in solid particles. Experiments were carried out at a velocity of 0.82 m/s, by varying the equivalent ratios ranging from 0.20 to 0.35, and analyzing the syngas composition, cold gas and carbon conversion efficiencies, lower heating value, and temperature distribution. An equivalence ratio of 0.30 was obtained for a bubbling fluidized gasifier with syngas compositions of 7.415%, 15.674%, 3.071%, 17.839%, and 56.031% for H2, CO, CH4, CO2, and N2, respectively. Under these conditions, we obtained cold gas and carbon conversion efficiencies and a lower heating value of 31.340%, 37.120%, and 3.881 MJ/Nm3, respectively.

Optimization of Sea Beach Sand Composition for Cast Iron Foundry Applications

The increasing demand and exorbitant use of river bed sand in foundries over the years have led to its depletion at an alarming rate. Consequently, many states in India have imposed severe restrictions on the mining of riverbed sand. Therefore, an effort is made to explore the potential use of sea sand for cast iron foundry applications. Experiments were performed for optimizing the composition of molding sand with respect to functional properties namely, strength, mold hardness, and permeability. The optimum composition of molding sand comprised of 8.33 wt% bentonite and 3.12 wt% moisture, and 88.54 wt% sea sand. Trials were conducted in a local foundry to ascertain the suitability of using a mixture of sea sand, bentonite, and water for producing defect-free gray iron casting. The trial was successful and parts were accepted for production purposes.

Effects of Different Magnetically Treated Waters on Emergence and Growth of Snail Medic

The present study concerns the effects of different magnetically treated waters (distilled water (as control), domestic water, saline water (-3 MPa), waste water and purified water of Arak city) on emergence and growth of Medicago scutellata (Var. Rabinson) seedlings under greenhouse conditions. The various waters were treated by passing it through 250 mT magnetic fields at flow rate of 2 lit/min. One hundred seeds per treatment were soaked in magnetically-treated waters for 12 hours and cultivated in pots with sand bed. The number of seedlings emerged was counted on daily basis, whereas growth data was measured on the 20th day after planting. Seedlings from exposed seeds to magnetically treated waters showed an improvement of 5-10 percent in the emergence and a 5-14 and 2-16 percent increase in root length and weight, respectively. Dry weight of emerged seedlings in pots by magnetically-treated waters, in comparison with those in untreated pots (control) increased for distilled water (14.4%), domestic water (16.3%), saline water (9.18%), and purified water (2.92%). The results of seedling lengths in the pots of magnetically-treated waters showed that, 5.54, 14.82, 14.67, 13.75, and 14.04 percent increased, respectively. From a practical point of view, it was concluded that could be a promising technique for agricultural improvements.

Flow regimes of submerged rectangular sharp-crested weirs in sand bed channel

Flow regimes of submerged rectangular sharp-crested weirs in sand bed channel

Subaqueous clinoforms created by sandy wave-supported gravity flows: Lessons from the Central California shelf

Subaqueous clinoforms are an important shelf feature. Their origins are typically associated with subaerial deltas but recent work has identified similar features in settings without a significant fluvial source (Mitchell, 2012; Patruno et al., 2015; Patruno and Helland-Hansen, 2018). These other studies have shown that such subaqueous clinoforms, also known as infralittoral prograding wedges (IPWs), are created largely by wave-induced processes. This study uses geophysical, sedimentological, and radiocarbon data to determine the sedimentary characteristics and genesis of a shore-parallel subaqueous clinoform developed far from any significant river on the central California continental shelf; a sedimentary shelf buildup known locally as the Cross Hosgri Slope. Sediment cores through the clinoformal sedimentary unit reveal that it is composed of beds with an erosive base, overlain by a thin (∼ 15 cm) coarsening upward sequence of shelly fine sands transitioning to a fining upward sequence marked by alternating parallel and ripple cross laminated very fine sands. The sedimentary succession is often capped by fine silts that are commonly interbedded with thin very fine sand beds. Radiocarbon dating of shells collected just above the erosive base indicate the subaqueous clinoform initiated progradation ∼7 ka, nucleating on an older Younger Dryas relict shoreface. We suggest the Cross Hosgri Slope was created by winter-storm waves mobilizing sands in water depths up to ∼70 m that transitioned into wave-supported gravity flows. The wave-supported gravity flows traveled downslope to water depths of up to ∼80 m, corresponding to the foot of the subaqueous clinoform. They did not travel beyond this depth as wave influence at these depths is negligible and the shelf gradient is insufficient to maintain movement of the load alone. Our work suggests that wave-supported gravity flows can entrain very fine sands and silts and build subaqueous clinoforms, even in the absence of a significant river source. Furthermore, we provide a facies model for sandy wave-supported gravity flow deposits.

On fluidising a heated bed of sand with a mixture of methane and air: When do the bubbles ignite and when does combustion occur between the sand particles?

Combustion in a heated bed of sand, fluidised by mixtures of CH4 and air, is inhibited. It was recently suggested that this is partly because a bubble only ignites, when the longest residence time of the fluidising gas passing through this bubble exceeds the ignition delay, tig, of the gas. This idea led to: (db/3Umf) ≥ tig as the condition for a bubble of diameter, db, to ignite. To test this, beds of sand (3 different sizes) were fluidised by different mixtures of CH4 and air. The bubbling bed was electrically heated slowly up to ∼ 1100 °C, whilst monitoring the bed's temperature and the composition of the gas at a fixed point in the bed. The temperature, at which bubbles ignited at this observation point, was identified as that of the bed, when the local concentration of CO reached a maximum. The mean size of the igniting bubbles was calculated from the flowrate of gas through the bed and the height above the distributor. Using tig (from the literature) at the measured ignition temperature, the above equation described the observations very satisfactorily. Thus, the fuel-richness of the fluidising gas and its temperature affect tig, Umf and db. Combustion of CO (or CH4) in the gas passing interstitially between fluidised sand particles was found to be unlikely, but can be promoted by fluidising large particles in a very hot bed, in which CO has a concentration larger than ≈ 10 vol.% at 1 at.

Survival of bovine-associated serotypes of Salmonella enterica in bedding sand

Cattle persistently infected with bovine-adapted serotypes of Salmonella enterica are an important animal health and food safety issue. One possible mechanism by which infection is sustained in a dairy herd is by survival of Salmonella in sand used as bedding material. In this study we assessed the survival of 107 to 108 cfu bovine-associated serotypes of Salmonella enterica (sv. Cerro, Dublin, and Heidelberg) in sterile sand, recycled bedding sand, and gray water collected from a Wisconsin dairy farm. All 3 serotypes persisted at relatively high numbers (>106 cfu/g) for at least 28 d in sterile sand, with Salmonella sv. Dublin decreasing less than 1 log10 over 70 d. To our surprise, when low numbers of Salmonella sv. Dublin (103 cfu) were inoculated into sterile sand, the organism multiplied within 3 d to approximately 106 cfu/g sand and persisted at that level for 28 d. When we inoculated Salmonella sv. Dublin into recycled bedding sand or sand taken directly from cow pens, we observed a significant decrease in colony-forming units by d 7. In contrast, we observed a significant increase in colony-forming units when Salmonella sv. Dublin was inoculated into gray water from the sand recycling system. These data demonstrate that Salmonella can persist for extended periods of time in bedding sand, although this is limited to some extent by the native microbiota in recycled bedding sand.

Procedures for diatom analyses and hydrodynamic separation of extreme wave paleo-deposits from tropical sediment environments

Diatoms are an important proxy in tsunami and storm research studies to determine potential sediment source and changes in environments pre- and post-event. However, the use of this proxy has proven challenging when studying extreme wave paleo events in sediments from the humid tropics because of the scarcity of diatoms in sand beds, and in clay or silt beds above and below. This problem has been associated with (1) dissolution of diatom valves in the humid tropics, (2) rate of burial and poor preservation of tsunami deposits, and (3) sediment and diatom size. Here we propose a practical solution to this problem – using hydrodynamic separation in the analysis of diatoms of extreme wave paleo-deposits. We compare diatom identification results from selected sand beds and units above and below, collected in a humid tropical environment (Guerrero, Mexico) using a standard procedure and the proposed fast hydrodynamic separation procedure to concentrate diatom-sized fraction. Thanks to the newly proposed methodology, the results showed a significant improvement in the number of observed diatom data in the studied sand units. We discuss two different techniques to achieve this aim and suggest how improvements on the quantitative research of diatoms from extreme wave deposits, particularly tsunamis, from the humid tropics.

The deflectors influence on flow complexity, bed morphology, sediment transport and water quality of urban lotic waters ‐ A laboratory study

AbstractIn this laboratory study different combinations of bed (sand, pebble gravel [gravel], and a mix of sand and gravel) and flow (typical and overtopping) were experimented with to investigate the impact of porous deflectors in flow diversity, water quality, and fish performance in prismatic open channels. Deflectors changed the gradually varied flow to a rapidly varied flow, as a sudden change in the water depth was observed at the deflectors, and this change was large for smooth beds. With the presence of gravel, the scouring near the downstream deflector was almost twice that of the sand bed, and with the scouring at its own upstream deflector, irrespective of whether the flow was typical or overtopping. This behavior was a result of sand mobilization due to shear stress and sand mobilization aided gravel transport. The mixed bed showed less gravel movement compared to the gravel‐only bed. The percentage of sediment washed out was minor for all bed scenarios, indicating that sediment transport was local. Relative to the sand bed without deflectors (representing a typical urban canal), deflectors resulted in reduced and improved water quality (in terms of sediment load) for sand, and mixed bed, respectively. The fishes found refuge and were comfortable in the pool areas created by deflectors unlike in channels without deflectors where they showed exhaustion.

Geocell-reinforced bed under static and cyclic loads: Soil density and grain size effects

This paper reports on a series of static and cyclic plate loading tests performed on a weak unreinforced sand bed in a test pit. The weak sand was covered by a 160 mm thick layer comprised of one of three compacted soil types which was either unreinforced or geocell-reinforced. The purpose was to investigate the effects of soil density and grain size as filler materials for the covering layer. The three covering soils were granular with average particle sizes of 2.2 (Soil 1), 6.14 (Soil 2), and 8.47 (Soil 3) mm. Under static loading, the bearing pressure increased on average 23% when the average grain size of the upper, unreinforced, soil layer changed from 2.20 mm to 8.47 mm. The improvement in bearing pressure was about 37% due to the use of a soil-filled geocell but, unlike the unreinforced situation, employing larger soil grains to fill the geocell pockets didn't show significant further improvement. For cyclic loading tests, the maximum settlement reduction by employing a geocell layer was about 50% for Soil 1. Whether loaded statically or cyclically, increasing soil density likely would be more efficient for improving geocell performance than employing a soil having larger particle sizes.