Transport Sediment Research Articles

Hydraulic effects of stormwater discharge into a small stream

The focus of this study is to describe the hydraulic effects of stormwater discharge, thus sediment transport occurring as a result of increased discharge from a stormwater detention pond, based on measurements made in a small high-slope Danish stream. In order to extrapolate the findings and predict the result of larger discharge flow rates from the detention pond in this study, 11 traditional threshold equations were tested, and results were compared to the sediment transport experiment with five formulas predicting the threshold based on shear stress and six based on stream power. The sediment transport experiment was constructed as a staircase pattern, step-wise increasing the discharge. During the experiment, measurements of sediment transport in the stream were made in two stations downstream from the point of discharge. Results from those measurements showed that there was no notable correlation between suspended sediment transport and bed sediment transport, and that suspended transport peaked during the periods of low flow conditions. Bed sediment transport peaked before the maximum flow, indicating that the available sediment for transport is a limiting factor. When comparing the calculated threshold of the collected sediment particle sizes to the shear stress and stream power calculated during the experiment, all 11 tested formulas overestimated the sediment transport and particle size moved by a specific flow. This result is in correspondence with results found in other experiments, and here the expected explanation is that the form roughness of the stream bed makes less energy available for sediment transport. This implies that the hydraulic impact from discharge of stormwater into small streams has to be evaluated on a case-by-case basis, rather than relying on general threshold sediment transport models.

Reach‐scale bankfull channel types can exist independently of catchment hydrology

AbstractReach‐scale morphological channel classifications are underpinned by the theory that each channel type is related to an assemblage of reach‐ and catchment‐scale hydrologic, topographic, and sediment supply drivers. However, the relative importance of each driver on reach morphology is unclear, as is the possibility that different driver assemblages yield the same reach morphology. Reach‐scale classifications have never needed to be predicated on hydrology, yet hydrology controls discharge and thus sediment transport capacity. The scientific question is: do two or more regions with quantifiable differences in hydrologic setting end up with different reach‐scale channel types, or do channel types transcend hydrologic setting because hydrologic setting is not a dominant control at the reach scale? This study answered this question by isolating hydrologic metrics as potential dominant controls of channel type. Three steps were applied in a large test basin with diverse hydrologic settings (Sacramento River, California) to: (1) create a reach‐scale channel classification based on local site surveys, (2) categorize sites by flood magnitude, dimensionless flood magnitude, and annual hydrologic regime type, and (3) statistically analyze two hydrogeomorphic linkages. Statistical tests assessed the spatial distribution of channel types and the dependence of channel type morphological attributes by hydrologic setting. Results yielded 10 channel types. Nearly all types existed across all hydrologic settings, which is perhaps a surprising development for hydrogeomorphology. Downstream hydraulic geometry relationships were statistically significant. In addition, cobble‐dominated uniform streams showed a consistent inverse relationship between slope and dimensionless flood magnitude, an indication of dynamic equilibrium between transport capacity and sediment supply. However, most morphological attributes showed no sorting by hydrologic setting. This study suggests that median hydraulic geometry relations persist across basins and within channel types, but hydrologic influence on geomorphic variability is likely due to local influences rather than catchment‐scale drivers. © 2020 John Wiley & Sons, Ltd.

Using spatial variations of grain size to reveal sediment transport in the Kumtagh Sand Sea, Northwest China

The identification of sediment transport processes is essential in understanding the accumulation and development of sand seas. However, only limited effort has been made to extract macroscale sediment transport information in aeolian science. In this study, we investigated grain-size variation to gain insight into large-scale sediment transport processes in the Kumtagh Sand Sea. Results suggest that grain-size variation is correlated to fluvial-aeolian interaction. In the central sand sea region, due to intermixed fluvial-aeolian controls, the downwind trend of grain size was significant except for the area surrounding the channel belt; but the grain-size trend in a downstream direction was not obvious. In the northeastern sand sea region, dune sand became progressively finer along a downwind direction, but sorting remained consistent. This phenomenon is ascribed to the fact that sand from upwind areas is mixed with local interdune sand. By combining evidence from dune patterns, grain sizes and mineral composition differences, we determined that sediment transport processes in the Kumtagh Sand Sea can be summarized as follows: Fluvial system transport sediments from the Altyn-Tagh Mountains to the sand sea, after which prevailing northerly winds subsequently rework these sediments and deliver them to downwind areas; meanwhile, sand from upwind areas is mixed with local sand in the northeastern sand sea region. Our findings provide insight into modern sand sea formation under the control of fluvial-aeolian interactions, while potentially offering further implications that can be used to explore paleogeographic process based on these modern processes.

Contourite porosity, grain size and reservoir characteristics

Contourites are now recognised as having a significant potential as hydrocarbon reservoirs in the subsurface, and several fields have been interpreted as comprising bottom-current reworked turbidite sands. However, very little has been published on the porosity characteristics of contourites. This study documents porosity data from IODP Expedition 339 sites in the Gulf of Cadiz. We use grain size analyses, porosity-depth plots and exponential models to yield a better understanding of grain size characteristics and facies, porosity characteristics, and the reservoir potential of contourites in the subsurface. New grain size data for over 350 samples from the Cadiz contourites is presented, building on earlier work. These data confirm the distinctive trends in textural properties linked to depositional processes under the action of bottom currents. The finest muddy contourites (<20 μm) show normal grain size distributions, poor to very poor sorting becoming better with decreasing grain size, and zero or low skewness. These are contourite-hemipelagite hybrids. Muddy to fine sandy contourites (20–200 μm) trend towards better sorting and initially fine-tail and then coarse-tail skew. These represent typical depositional trends for contourites, affected by current capacity and then increased winnowing at higher current speed. Clean sandy contourites (around 200 μm) are the best sorted. Medium and coarser-grained contourites show a trend towards poorer sorting. They result from the action of dominant bedload transport, extensive winnowing, and mixed sediment supply. Porosity-depth relationships from four Cadiz sites show a moderately high initial porosity for both sand and mud facies (50–60%) and a systematic decrease with depth to around 35–40% near 500 m burial depth. According to the exponential models of porosity with depth, contourite porosity should exceed 10% at 2500 m burial depth. We compare the data from the Gulf of Cadiz Contourite Depositional System, with those of the Eirik Drift, Newfoundland Drift, Gardar Drift and Canterbury Slope Drifts. Similar depth trends are observed, and all show anomalies linked to interbedded sandy and muddy facies, composition (carbonate vs siliciclastic), and the presence of hiatuses in the sediment record. These data provide good insight into the likely reservoir characteristics of contourites, for both conventional and unconventional reservoirs. They are comparable with those of existing contourite fields, most of which are mixed turbidite-contourite systems.

Suspended sediment yield modeling in Mahanadi River, India by multi-objective optimization hybridizing artificial intelligence algorithms

River sediment produced through weathering is one of the principal landscape modification processes on earth. Rivers are an integral part of the hydrologic cycle and are the major geologic agents that erode the continents and transport water and sediments to the oceans. Estimation of suspended sediment yield is always a key parameter for planning and management of any river system. It is always challenging to model sediment yield using traditional mathematical models because they are incapable of handling the complex non-linearity and non-stationarity. The suspended sediment modeling of the river depends on the number of factors such as rock type, relief, rainfall, temperature, water discharge and catchment area. In this study, we proposed a hybrid genetic algorithm-based multi-objective optimization with artificial neural network (GA-MOO-ANN) with automated parameter tuning model using these factors to estimate the suspended sediment yield in the entire Mahanadi River basin. The model was validated by comparing statistically with other models, and it appeared that the GA-MOO-ANN model has the lowest root mean squared error (0.009) and highest coefficient of correlation (0.885) values among all comparative models (traditional neural network, multiple linear regression, and sediment rating curve) for all stations. It was also observed that the proposed model is the least biased (0.001) model. Thus, the proposed GA-MOO-ANN is the most capable model, compared to other studied models, for estimating the suspended sediment yield in the entire Mahanadi river basin, India. The results also suggested that the proposed GA-MOO-ANN model is unable to estimate suspended sediment yield satisfactorily at gauge stations having very small catchment areas whereas performing satisfactorily on locations having moderate to the large catchment area. The models provide the best result at Tikarapara, the gauge station location in the extreme downstream, having the largest catchment area.

Comparison of historical and modern river surveys reveal changes to waterhole characteristics in an Australian dryland river

Human activities are known to impact the physical template of river channels. These impacts can result from deliberate, direct modifications as well as via indirect processes linked to broadscale landscape change. This study examined changes in the physical template of the Barwon-Darling River, a dryland river in southeastern Australia. Historical longitudinal profiles from the late 1800s were compared with contemporary profiles derived from high-definition, side scanning sonar. Comparisons focused on characterising waterhole features as they are a critical biophysical component of dryland rivers. The use of historical data presented several challenges related to small sample size and suspected sampling bias in the historical survey. However, this study demonstrates that these issues are not insurmountable providing the limitations and uncertainties with the data are acknowledged and data analyses are limited to parameters that can distinguish genuine landscape change. The findings revealed a dramatic change in the physical template of the Barwon-Darling River over a 120-yr period. Waterhole depths and distances between waterholes have been altered significantly. The magnitude and trajectory of change was found to be scale-dependent, with the greatest observable change aligned with the presence or absence of low-level weirs. Waterholes influenced by low-level weirs have increased in depth because of localised impoundment, whilst the distance between deep waterholes (>4 m in depth) has declined substantially. In contrast, the maximum depths of waterholes located outside the influence of weir pools has declined by 1.6 m and the distance between deep waterholes has more than doubled in several reaches. These declines are likely to be caused by sediment accumulation in waterholes associated with anthropogenic increases in sediment flux and a decline in the river's capacity to entrain and transport sediment throughout the system.

The performance of low crested breakwaters as a sand trap for shore protection

The low crested breakwater (LCB) is considered as a new coastal protective structure which has not been widely used compared to other coastal protection structures. LCB has more advantages than conventional ones such as breakwaters, requiring lower cost and aesthetically not disturbing nature because of its position which is below sea level so it is suitable for beach tourism.Studies on low crested breakwaters are mostly about the ability to absorb energy waves and how beach responded to the structure. However, the study on the ability of this low crested breakwater such as a sand trip is still limited. Therefore, this study aims to observe the breakwater’s performance as a sand trap for shore protection and the effect of the parameters on the performance.This study was conducted on the plexiglass wave made with a length of 18 m, a width of 0.3 m and a depth of 0.45 m. Wave parameters (height and period) and structure parameters (height and width) were employed as a reference in this study. This research was conducted by varying the waves, height and water depth. The results indicate that the number of transport sediment tends to be increased following the wave height (Hi), the water depth at the height of the structure (Rc) and reduced wavelength (L). The type and position of a wave breaking also affect the amount of transport sediment.

Multi-objective genetic algorithm optimization of artificial neural network for estimating suspended sediment yield in Mahanadi River basin, India

ABSTRACTRivers are an integral part of the hydrological cycle and are the major geological agents which erode the continents and transport water and sediments to the oceans. Thus rivers act an important link between continents and oceans for the mass balance. Estimating the suspended sediment yield is one of the crucial aims in the field of managing, designing and planning of any river system or reservoir. To determine the suspended sediment yield in a river basin demands more labour or it is more costly when automatic sampling devices are used. The number of variables and the inter-relationship existing among them influence the suspended sediment yield and the nature of these inter-relationships is neither linear nor simple. Unfortunately, it is a difficult task to determine the suspended sediment yield when traditional mathematical models are used as complex variables and processes are involved. The major key factors, such as basin geology (rock type), relief, rainfall, temperature, water discharge and catchment area that affect sediment yield, are used as inputs to develop the model for predicting the suspended sediment yield in the Mahanadi River. In this paper, a multi-objective genetic algorithm for artificial neural network (MOGA-ANN)-based approach is used for predicting the suspended sediment yield. The MOGA assists ANN to minimize the two competing objectives, i.e. mean error and variance simultaneously. Thus in this study, a hybrid artificial intelligence-based method, MOGA-ANN model, is developed using the hydro-geological-climatic factors where all parameters associated with the ANN models are optimized simultaneously using MOGAs to estimate the suspended sediment yield in the Mahanadi River basin. The ANN's parameters are optimized globally by the MOGA to accurate estimation. The study has been carried out to develop MOGA-ANN for estimating the suspended sediment load using 20-year data at the Tikarapara gauging station which is the last downstream station in the Mahanadi River. The MOGA-ANN model provided the root mean square error 0.0281, correlation coefficient (r) 0.966 and efficiency factor 0.919 during the testing phase. The results suggested that the hybrid MOGA-ANN model exhibited satisfactory performance with an accuracy of 96.41%.

Morphodynamics of river and coastal transport of sediments in mega delta basin, Niger Delta Nigeria

Niger delta is recognized as the third mega deltas in the history of mankind. Understanding the sediment dynamics and morphodynamics relationship between the morphology of the bedrocks to the hydrodynamic of its transport sediments is crucial for water bodies’ preservation, conservation, and sustainability. Sediments transportation in Niger delta involves a two-phase flow system in which one phase is considered to be fluid and the other phase is solid. The water bodies is seldom saturated with sediments occasioned by irregular solid waste dumps, erosions debris, and transported at ease without any form of management or control for many years now. Consequently, poor water resources, agriculture and fishery production are at extreme lost as sediment transport and deposition influences great magnitude of useful river dynamics. Therefore, the objective of this study is focused on whether sediment transport has an effect on the morphology of the channel in the Niger Delta basin. It is necessary to determine the relationship between these two key variables; Sediment yield and channel morphology. A correlation matrix was generated in MS Excel to determine the underlying relationship between the variables under study with a coefficient of determination of 11.23% and a positive correlation between suspended sediment yield, bed load and channel morphology of +0.345. The paper will be useful to research institutions, water resources agencies, government and environmental experts and engineers.

Transport of nano zerovalent iron (nZVI) coupling with Alcaligenes sp. strain in porous media.

Coupling nano zerovalent iron (nZVI) particles with anaerobic bacteria is a potentially powerful approach for remediating polluted groundwater. However, little is known about the transport of these mixed systems in porous media, which could potentially affect the system's activity and half-life in aqueous environments. This study assessed the transport and stability of nZVI coupled with Alcaligenes sp. TB by column experiments and sedimentation tests. The results showed that combined bio-nZVI systems experienced significantly higher transport and lower sedimentation rates than stand-alone nZVI. The transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images showed that Alcaligenes sp. TB reduced aggregation of nZVI to some extent, though slight toxicity to bacteria was observed. The results of ζ-potential measurements demonstrated that the presence of bacteria increased the electrostatic force between the particles. Voltammetry, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analysis confirmed that the bio-nZVI system undergoes different redox processes. The presence of bacteria favored the formation of FeOOH not Fe2O3 or Fe3O4, resulting in weaker surface magnetic properties.

Impacts of tidal-channel connectivity on transport asymmetry and sediment exchange with mangrove forests

Mangrove forests provide many valuable services, including wave- and tidal-energy dissipation, sediment accumulation, and substrate stabilization. But, their global extent is rapidly shrinking. Sedimentary research that is needed to inform restoration projects has so far focused on characterizing flow patterns through forests associated with single rivers, nearshore environments, or terminating tidal channels. However, flows within the most extensive mangrove forests tend to be driven through channels that connect to multiple estuaries or other channels with temporally lagged tides. For this study, in-situ observations of water and sediment flux were obtained in two tidal channels near the Amazon River to characterize how connectivity impacts sediment transport in coastal mangrove forests. The low-connectivity channel connects to one estuary whereas the high-connectivity channel connects two estuaries. We conclude that channel connectivity controls the amount of sediment stored in channels that is available to supply mangrove forests. Although phase-duration asymmetry is flood dominant in both channels, velocity asymmetry becomes ebb dominant during tidal cycles when the mangrove flats are inundated. Additionally, tidal elevation and water velocity are not in quadrature for the high-connectivity channel, as they are for the low-connectivity channel. As a result, the high-connectivity channel acts as a conduit for sediment from one estuary to another rather than simply importing and retaining sediment like the low-connectivity channel. High-connectivity channels distribute point-source sediment along coastlines and provide sediment to estuaries and channels that may not have their own direct source. As restoration efforts of mangrove forests continue to grow in response to coastal threats such as sea-level rise and diminished fluvial-sediment delivery, the location of these efforts can benefit from the conclusion that channel connectivity influences spatial dispersal of sediment supply to mangrove forests.

Měkkýší fauna (Gastropoda, Bivalvia) z lokality Mušlov (vídeňská pánev)

The Mušlov locality is situated 3.5 km ESE from the town of Mikulov and it is a part of the Vienna Basin. On the locality a profile rich in shallow-water middle Miocene (Badenian) fauna was uncovered. Its substantial part was deposited in fine-grained calcareous sand, to a lesser extent the fauna also occurred in pebbles and blocks of gray algal limestones. Mainly stone cores with calcareous and degrading shells were found in the limestones, while in the calcareous sands the fossils were well preserved. A rich set of small fauna from fine-grained sand was obtained by washing of samples. There have been determined 73 species of Gastropoda and 25 species of Bivalvia. The most abundant species of gastropods are Tricolia eichwaldi, Rissoina podolica, Bittium reticulatum, Gibbula aff . umbilicalis, Jujubinus striatus, Neritina picta and Turritella bicarinata. Among bivalves the most abundand species are Cardites partschi partschi and Linga columbella. Quantity and degree of conservation of fauna indicate minimal transport and slow sedimentation on the sea floor. Based on the found species, the fauna was mainly bound to a fine-grained substrate but there were also species that preferred the solid substrate. The abundant occurrence living on algal species is evidenced by their rich stands. The fauna lived in the shallow sea with a good oxygenation and a normal salinity. The occurrence of some species documents a warm sea between 20–28 °C.

Simulating a Watershed-Scale Strategy to Mitigate Drought, Flooding, and Sediment Transport in Drylands

Drylands today are facing a landscape-scale water storage problem. Throughout the increasingly arid Southwest of the United States, vegetation loss in upland watersheds is leading to floods that scour soils and transport sediment that clogs downstream riparian areas and agricultural infrastructure. The resulting higher flow energies and diminished capacity to infiltrate flood flows are depleting soil water storage across the landscape, negatively impacting agriculture and ecosystems. Land and water managers face challenges to reverse the trends due to the complex interacting social and biogeophysical root causes. Presented here is an integrative system dynamics model that simulates innovative and transformative management scenarios. These scenarios include the natural and hydro-social processes and feedback dynamics critical for achieving long-term mitigation of droughts, flooding, and sediment transport. This model is a component of the Flood Flow Connectivity to the Landscape framework, which integrates spatial and hydrologic process models. Scenarios of support and collaboration for land management innovations are simulated to connect flood flow to the floodplains throughout the watershed to replenish soil storage and shallow groundwater aquifers across regional scales. The results reveal the management policy levers and trade-off balances critical for restoring management and water storage capacity to the system for long-term resilience.

Numerical Simulation of Ocean Wave Using High-Order Spectral Modeling Techniques: Its Influence on Transport Sediment in Benoa Bay, Bali, Indonesia

Benoa Bay is threatened by sedimentation issue within the bay. It impairs the water mass circulation, influencing scour, mixing, and turbulence as well as sediment transport processes. This study focuses on the wave characteristic and its relation to sediment transport within Benoa Bay. Spectral wave modeling techniques were employed. The equation was discretized based on the condition of winds, tidal, and currents. Total sediment transported was calculated according to the wave model result. Total suspended sediment (TSS) model was simulated which the simulation considers bed load and suspended load transport. Significant wave height (Hs) ranged 0-0.48 m and 0-0.44 m during high tidal condition and low tidal condition respectively. Wave undulation propagates toward the West and Northwest within Bay. The wave period (Ts) ranged 2-6.5 second. Total sediment transport ranged 2828.16 - 86235.66 m3/year. TSS concentration ranged 1-100 mg/L and 1-155 mg/L during high tidal condition and low tidal condition respectively. Those conditions indicate that the sedimentation has been extremely occurred within the bay. The areas around Benoa peninsula, Benoa harbor, and Serangan Island are heavily polluted by suspended sediment. Bottom sediment is stirred by hydraulic jump off wave propagation. The first wave crest induces scour, which its train carries the stirred sediment entering the bay. If ongoing, this condition will exacerbate the existing ecosystem. Benoa Bay development has a big role evoking the level of TSS and turbidity. The more the sedimentation occurs, the more the ecological problem takes place.

Natural and Anthropogenic Sediment Mixing Processes in the South-Western Baltic Sea

Natural and anthropogenic sediment mixing can significantly impact the fidelity of sedimentary records of climate and environmental variability and human impact. This can lead to incorrect interpretations of the previous state(s) of a given ecosystem, its forcing mechanisms, and its future development. Here, natural and anthropogenic sediment mixing processes (i.e. bioturbation, hydroturbation and direct anthropogenic impact) are investigated in the south-western Baltic Sea by sedimentological, ichnological, geochemical, and radionuclide analyses to assess their impact on time-marker profiles and sediment deposition. Depth profiles of mercury and caesium-137 display a varyingly strong disturbance down to 5-25 cm. The deviations from undisturbed profiles can be used to estimate the relative degree of sediment mixing. Sedimentary fabric analysis of high-resolution X-radiographs provides further insight into bioturbation. Ichnofossils identified in short sediment cores suggest that the primary sedimentary structure is partly overprinted by burrowing organisms living in the upper 5-7 cm of sediment. Meteorological and hydrological data from automated measuring stations combined with results from resuspension experiments show that hydrodynamic events, such as storms and saline water inflows from the North Sea, have the potential to resuspend and laterally transport sediment particles in the south-western Baltic Sea. Partially graded layers in the scale of mm to cm in the investigated cores are likely associated with such hydrodynamic events. Multiple generations of linear traces on the seafloor are made visible through sidescan-sonar mapping and document a strong anthroturbation in the muddy sediments of the Mecklenburg Bight and the Arkona Basin, e.g. by bottom trawling. Depending on the core location and assumed mixing depth, determined mean net linear sedimentation rates range between 0 and 3.5 mm/a and reconstructed net mass accumulation rates range between 0 and 1.86 kg/m2/a in the mud basins. The calculable inventory of anthropogenic contaminants in the sediments illustrates the important, at least temporary storage function of the mud basins and of the adjacent sandy areas over industrial times. The findings of this study help identify the influence of natural and anthropogenic mixing on sediment profiles, and demonstrates the use of mixed sediment profiles for inferring information about past environmental conditions and anthropogenic impact.

Dye-tracer technique for rill flows by velocity profile measurements

Water flow on hillslope soil surface supplies energy which is required to detach soil particles, to transport and deposit sediments, therefore flow velocity is a key variable related to hillslope hydrodinamics of soil erosion processes. Among the different methods available for measuring velocity of shallow interrill and rill flow, the trace technique is widely used. Trace technique is applied by adding a material (salt, magnetic material, water isotope, floating object) and then measuring the speed of the material to travel a known distance from the injection point.When flow velocity is measured using a dye-tracing method, the mean velocity is calculated by multiplying the measured surface velocity of the leading edge of the tracer plume by a correction factor which was generally empirically deduced. The main uncertainty of the dye-tracing technique stands in the estimate of this correction factor, which is the ratio between the mean flow velocity and the surface velocity. The main goal of this paper is establishing a theoretical relationship for calculating the correction factor by using a power velocity profile. At first, the developed analysis demonstrated that the correction factor only depends on the exponent of the power velocity distribution (Eq. (5)). Then, this theoretical expression of the correction factor was applied using the velocity profiles measured by Baiamonte and Ferro for the condition of sediment-free flow in motion on a rough bed and by Coleman for a sediment-laden flow moving on a smooth flume.Using the correction factor values calculated by the velocity measurements carried out for the sediment-free flow in motion on a rough bed, the relationship between the correction factor and roughness height was established. In agreement with a previous study by Ali et al., for a sediment-free flow the correction factor increases with roughness height.Finally, the velocity profile measurements carried out for a sediment-laden flow in motion on a smooth bed were used to state the effect of sediment load on the correction factor. This last analysis allowed to conclude, in agreement with Li and Abrahams and Zhang et al., that the correction factor decreases when the sediment load increases.

A Well‐Posed Alternative to the Hirano Active Layer Model for Rivers With Mixed‐Size Sediment

The active layer model (Hirano, 1971) is frequently used for modeling mixed‐size sediment river morphodynamic processes. It assumes that all the dynamics of the bed surface are captured by a homogeneous top layer that interacts with the flow. Although successful in reproducing a wide range of phenomena, it has two problems: (1) It may become mathematically ill‐posed, which causes the model to lose its predictive capabilities, and (2) it does not capture dispersion of tracer sediment. We extend the active layer model by accounting for conservation of the sediment in transport and obtain a new model that overcomes the two problems. We analytically assess the model properties and discover an instability mechanism associated with the formation of waves under conditions in which the active layer model is ill‐posed. Numerical simulations using the new model show that it is capable of reproducing two laboratory experiments conducted under conditions in which the active layer model is ill‐posed. The new model captures the formation of waves and mixing due to an increase in active layer thickness. Simulations of tracer dispersion show that the model reproduces reasonably well a laboratory experiment under conditions in which the effect of temporary burial of sediment due to bedforms is negligible. Simulations of a field experiment illustrate that the model does not capture the effect of temporary burial of sediment by bedforms.

Studi Sedimentasi di Sungai Batang Lampasi Sedimentation Study at Batang Lampasi River

BatangLampasi River was located in Talawi village, Nagari Koto Nan GadangPayakumbuh, about 30 km from Bukittinggi, with 48.19 km river length and around 226 km2 Cathment Area. The river flow carries a lot of sediment material, causing siltation on the riverbed which causes the river to overflow in the surrounding area. Sediment transport was triggered by Lampasi watershed erosion, that especially in the upstream section and settling on the riverbed. Prediction of depth decrease caused by sedimentation was conducted. Theoretical flood discharge determined used Nakayasu method. Sediment yield caused by land erosion determined by USLE equation and will compared with total sediment transport that calculated for 5 years return period with Yang's, Engelund Hansen, Ackers and White's methods. HEC-RASS 4.0 was used to find the high of flood water level and also as input hydraulics term to calculating transport sediment. The equivalent value approaching sediment yield was Yang's method where the sediment transport value is 21294,763 tons / year with sediment thickness of 27.24 cm / year. With these deposits thickness we can see from HEC-RASS 4.0 modeling the elevation of high flood water during normal conditions and the presence of thick sediment deposits.

Estimating sediment yield at Kaduna watershed, Nigeria using soil and water assessment tool (SWAT) model

Over the years, sedimentation has posed a great danger to the storage capacity of hydropower reservoirs. Good understanding of the transport system and hydrological processes in the dam is very crucial to its sustainability. Under optimal functionality, the Shiroro dam in Northern Nigeria can generate ∼600 MW, which is ideally sufficient to power about 404,000 household. Unfortunately, there have not been reliable monitoring measures to assess yield in the upstream, where sediments are sourced into the dam. In this study, we applied the Soil and Water Assessment Tool (SWAT) to predict the hydrological processes, the sediment transport mechanism and sediment yield between 1990 and 2018 in Kaduna watershed (32,124 km2) located upstream of the dam. The model was calibrated and validated using observed flow and suspended sediment concentration (SSC) data. Performance evaluation of the model was achieved statistically using Nash-Sutcliffe (NS), coefficient of determination (r2) and percentage of observed data (p-factor). SWAT model evaluation using NS (0.71), r2 (0.80) and p-factors of 0.86 suggests that the model performed satisfactorily for streamflow and sediment yield predictions. The model identified the threshold depth of water (GWQMN.gw) and base flow (ALPHA_BF.gw) as the most sensitive parameters for streamflow and sediment yield estimation in the watershed. Our finding showed that an estimated suspended sediment yield of about 84.1 t/ha/yr was deposited within the period under study. Basins 67, 71 and 62 have erosion prone area with the highest sediment values of 79.4, 75.1 and 73.8 t/h respectively. Best management practice is highly recommended for the dam sustainability, because of the proximity of erosion-prone basins to the dam.

Erosion rates and patterns in a transient landscape, Grand Staircase, southern Utah, USA

AbstractCosmogenic 10Be concentrations in alluvial sediment are widely used to infer long-term, catchment-averaged erosion rates based on the assumption that the landscape is in mass-flux steady state. However, many landscapes are out of equilibrium over millennial time scales due to tectonic and climatic forcing. The Grand Staircase of the Colorado Plateau (North America) is a transient landscape, adjusting to base-level fall from the carving of the Grand Canyon, and is characterized by cliff-bench topography caused by differential erosion of lithologic units. The 10Be concentrations from 52 alluvial and colluvial samples, collected in nested fashion from five catchments, produced inferred erosion rates ranging from 20 to &gt;3500 m/m.y. (or mm/k.y.). We attribute this high variance in part to lithologic-controlled steepness and hotspots of erosion related to cliff retreat along the White Cliffs (escarpment near Mt. Carmel Junction, Utah), as well as headward drainage expansion along the uppermost Pink Cliffs (escarpment within Bryce Canyon National Park). Results from the downslope Vermillion Cliffs (near Kanab) indicate lower erosion rates despite similar slope and rock types, suggesting knick-zone migration has passed that lower region of our study area. The 10Be concentrations measured along trunk streams systematically match local, subcatchment erosion rates, with muted influence from upstream sediment sources. This is consistent with intermittent sediment conveyance between cliff and bench terrain, with sediment storage and localized release associated with ephemeral arroyo systems in the region. Therefore, while detrital cosmogenic nuclide records in transient landscapes may not directly reflect upstream catchment-averaged erosion rates, 10Be inventories can provide insight into unsteady upslope-directed erosion and downslope-directed sediment conveyance in these dynamic landscapes.