Estimation Of Sediment Transport Research Articles

Applicability of sediment transport models to evaluate medium term evolution of tidal inlet systems

This paper derives local formulae to estimate bed roughness and suspended transport and present a method to calculate net sediment transport at tidal inlet systems, combining field data and a range of well established empirical formulations. To accomplish this, measurements spanning a spring-tidal cycle of mean water levels, waves, near-bed flow turbulence and bed forms were obtained from the Ancão Inlet, Ria Formosa lagoon system, Portugal. High-resolution hydrodynamic data were gathered using acoustic equipments and by measuring sediment properties (grain-size diameter and bed form dimensions) under fair-weather conditions. The results compared favourably with available direct and indirect field observations of sediment transport rates. The approach appears to be robust and widely applicable and so can be applied to the same conditions in any tidal inlet system. This is of particular importance when attempting to understand sediment transport at inlet mouths, and has practical applications in a range of coastal engineering and coastal management areas concerned with navigation safety, coastal erosion, ecosystem health and water quality. The study discusses the applicability of the method on evaluating system flushing capacity, giving important insights on multiple inlet evolution, particularly with regard to their persistence through time. The methodological framework can be applied to assess the long-term stability of single- and multiple-inlet systems, provided that estimates of sediment storage at ebb-tidal deltas are available and sediment transport estimates during storm events are statistically considered.

An approach to estimating sediment transport capacity of overland flow

Estimating sediment transport capacity of overland flow is essential to the development of physically based soil erosion models. Correlation analysis indicates that stream power is a dominant factor for sediment transport in overland flows and a new sediment transport capacity equation is proposed based on dimensional analysis. The coefficients of the new equation are calibrated using the published laboratory data, and rainfall impact is taken into consideration by adding an empirical factor on the dimensionless critical stream power. The new sediment transport capacity equation is a function of stream power, rainfall impacted critical stream power and slope. The new equation is applied in a one-dimensional soil erosion model to simulate field data of a runoff plot and the simulation results are reliable.

Channel morphometry, sediment transport, and implications for tectonic activity and surficial ages of Titan basins

Fluvial features on Titan and drainage basins on Earth are remarkably similar despite differences in gravity and surface composition. We determined network bifurcation ( R b ) ratios for five Titan and three terrestrial analog basins. Tectonically-modified Earth basins have R b values greater than the expected range (3.0–5.0) for dendritic networks; comparisons with R b values determined for Titan basins, in conjunction with similarities in network patterns, suggest that portions of Titan’s north polar region are modified by tectonic forces. Sufficient elevation data existed to calculate bed slope and potential fluvial sediment transport rates in at least one Titan basin, indicating that 75 mm water ice grains (observed at the Huygens landing site) should be readily entrained given sufficient flow depths of liquid hydrocarbons. Volumetric sediment transport estimates suggest that ∼6700–10,000 Titan years (∼2.0–3.0 × 10 5 Earth years) are required to erode this basin to its minimum relief (assuming constant 1 m and 1.5 m flows); these lowering rates increase to ∼27,000–41,000 Titan years (∼8.0–12.0 × 10 5 Earth years) when flows in the north polar region are restricted to summer months.

A HYBRID MODEL OF SWASH-ZONE LONGSHORE SEDIMENT TRANSPORT ON REFLECTIVE BEACHES

The hydrodynamics and sediment transport in the swash zone is currently outside the domain of coastal-area models, which is a significant limitation in obtaining littoral sediment-transport estimates, especially on steep reflective beaches where the waves practically break on the beachface. In this study, an existing process-based coastal model (MIKE 21) is combined with a theoretical derivation of swash processes, resulting in an innovative hybrid modelling approach that is capable of estimating longshore sediment transport in the swash zone. The method relies upon estimation of swash hydrodynamics from an extended ballistic swash model with friction included. The terminal bore and other incident wave properties were computed from the output of a spectral-wave model (MIKE 21 SW). The Bagnold-type equation was applied to estimate gross transport volumes and the longshore component was computed for the sand volume displaced during the up-rush. The newly developed hybrid modelling approach was applied to Jimmys beach, a steep reflective beach (D50 = 0.3 mm, gradient=0.1) along the northern shoreline of Port Stephens, Australia. The model results yield the alongshore swash transport pathways and the indicative transport volumes. A point of divergence is identified at the beach erosion area, which is of critical importance in terms of shoreline erosion and management. The preliminary results suggest that swash-zone transport can account for a large percentage of the total littoral drift for such beaches. However, further field or laboratory data are required to test model utility, as well as to tune calibration parameters based on the site-specific conditions.

Estimation of suspended sediment transport in the Kebir drainage basin, Algeria

Sediment load and sediment concentration are highly important variables that may play a key role in environment quality assessment and help to evaluate the extent of potential adverse impacts. This paper introduces a methodology to predict sediment loads in the Kebir drainage basin (681 km2). The methodology is developed by a conventional sediment rating curve and a multiple regression model. The former method is investigated with the mean discharge classes derived from the recorded instantaneous suspended sediment concentrations and water discharges for the Kebir basin, prior to the Mexa reservoir construction. The latter is based on rock type erodibility, mean annual runoff and basin area variables, and which is applied for the ungauged Mexa reservoir basin located upstream of the Kebir gauging station (651 km2). The mean annual suspended sediment yield of both Kebir drainage basin and Mexa reservoir basin conducted during the 24 years (1975/1976–1998/1999) and the 9 years (1999/2000–2007/2008) are respectively 895 T km2 year-1 and 572 T km2 year-1. Despite the decline in sediment load during the reservoir period due mainly to disturbance in climatic regime, the basin is suffering severe soil loss, and currently 0.42% y-1 in loss of storage in the reservoir due to sedimentation has been evaluated. The high amount of sediment produced from the study drainage basin is a function of climatic and several physical factors including the high proportion of argillaceous materials and the amount of bare soil exposed.

Estimating Alongshore Sediment Transport and the Nodal Point Location on the Delaware–Maryland Coast

An approach to estimating sediment transport along the Delaware–Maryland coast is described. Wave information study (second generation model, WISWAVE 2.0) hindcast frequency-direction spectra from 1980 to 1999 are used to generate a radiation stress-conserving angle for bringing offshore waves to breaking to estimate alongshore sediment transport. Using standard values for the coefficients in the United States Army Corps of Engineers’ Coastal Engineering Research Center (CERC) equation yields 20-year mean alongshore sediment transport rates between 470,942 and −517,088 m3 /year depending on alongshore location after shoaling waves to shore. Interannual variability is large with SDs between 95,078 and 241,313 m3 /year again depending on alongshore location. Alongshore sediment transport rate estimates are commensurate with past studies using WIS data but overpredict the typically cited value of ∼100,000 m3 /year near Indian River Inlet, Delaware based on sediment budget data by a factor of 3–4. This ove...

Estimating sediment transport from acoustic measurements in the Venice Lagoon inlets

This paper presents the results of a 3-year-long (November 2004–November 2007) study based on the use of acoustic Doppler current profilers (ADCPs) to estimate the solid transport through the three inlets of Venice lagoon. In each of the three inlets instruments were mounted both on survey boats and deployed on the channel bed. The three bottom-mounted ADCPs were positioned in the central part of the inlets, continuously monitoring vertical profiles in the water column. Periodic transects along the investigated sections were collected by the boat-mounted ADCP. Both installations measured current speed and acoustic backscatter intensity. The latter expresses the attenuation of acoustic energy due to material in the water column. The conversion of acoustic backscatter into suspended solids concentration (SSC) was carried out by means of direct measurements of concentration; also an indirect method was used. Boat-mounted ADCP acquisitions were used to calibrate and to validate the bottom-mounted ADCP data. Hourly time series of water discharge and SSC were obtained by calculation from the current speed and acoustic backscatter data recorded by the fixed ADCPs. Hourly solid flux time series were computed. The solid flux and SSC time series at the three inlets were analyzed in relation to the hydrodynamic and atmospheric conditions, highlighting the impact of intense meteorological events on the resuspension process. The lagoon sediment budget is estimated to be about 0.5×10 6 t/yr and shows a tendency for sediment loss.

Episodic and Long-Term Sediment Transport Capacity in The Hudson River Estuary

A tidally averaged model of estuarine dynamics is used to estimate sediment transport in the Hudson River estuary over the period 1918 to 2005. In long-term and seasonal means, along-channel gradients in sediment flux depend on the estuarine salinity gradient and along-channel depth profile. Lateral depth variation across the estuary affects the near-bottom baroclinic circulation and consequently the direction of net sediment flux, with generally up-estuary transport in the channel and down-estuary transport on the shoals. Sediment transport capacity in the lower estuary depends largely on river discharge, but is modified by the timing of discharge events with respect to the spring–neap cycle and subtidal fluctuations in sea level. Sediment transport capacity also depends on the duration of high-discharge events relative to the estuarine response time, a factor that varies seasonally with discharge and estuarine length. Sediment fluxes are calculated with the assumption that over long periods, the system approaches morphological equilibrium and sediment accumulation equals sea level rise. The inferred across- and along-channel distributions of sediment erodibility correspond with observations of bed properties. Equilibrium is assumed at long time scales, but at annual to decadal time scales the estuary can develop an excess or deficit of sediment relative to equilibrium. On average, sediment accumulates in the estuary during low- and high-discharge periods and is exported during moderate discharge. During high-discharge periods, maximum export coincides with maximum sediment supply from the watershed, but the nearly cubic discharge dependence of fluvial sediment supply overwhelms the roughly linear increase in estuarine transport capacity. Consequently, sediment accumulates in the estuary during the highest flow conditions. Uncertainty remains in the model, particularly with sediment properties and boundary conditions, but the results clearly indicate variability in the sediment mass balance over long time scales due to discharge events.

Modified logarithmic tachoida applied to sediment transport in a river

In this paper, a modified tachoida is applied to the estimation of sediment transport in a river. Eddy viscosity coefficient at the bottom which satisfied hydrodynamics stability of the flow is related to the sediment concentration. On this basis it was possible to determine the sediment stream in the river based on the bottom sediment composition.

Riparian Sediment Delivery Ratio: Stiff Diagrams and Artificial Neural Networks

Various methods are used to estimate sediment transport through riparian buffers and grass filters, with the sediment delivery ratio having been the most widely applied. The U.S. Forest Service developed a sediment delivery ratio using the stiff diagram and a logistic curve to integrate some of the factors influencing sediment delivery heuristically. This study independently tested the Forest Service sediment delivery ratio contrasted with artificial neural networks to represent the multiple nonlinearities between important factors and sediment delivery. The Forest Service sediment delivery ratio was not adequate when compared to published sediment yields from 30 small experimental buffers from three countries, including four forested buffers. However, artificial neural networks gave estimates of the delivery ratio that were highly correlated to the observations. The 30 buffer observations produced such good estimates of the sediment delivery ratio with both seven and five buffer parameters that this study suggests that as few as 30 sediment yield observations can be the basis for applying neural networks to interpolate the complex, multiple nonlinearities of hydrology and sediment transport on riparian buffers.

A conceptual framework for dryland aeolian sediment transport along the grassland–forest continuum: Effects of woody plant canopy cover and disturbance

Aeolian processes are of particular importance in dryland ecosystems where ground cover is inherently sparse because of limited precipitation. Dryland ecosystems include grassland, shrubland, savanna, woodland, and forest, and can be viewed collectively as a continuum of woody plant cover spanning from grasslands with no woody plant cover up to forests with nearly complete woody plant cover. Along this continuum, the spacing and shape of woody plants determine the spatial density of roughness elements, which directly affects aeolian sediment transport. Despite the extensiveness of dryland ecosystems, studies of aeolian sediment transport have generally focused on agricultural fields, deserts, or highly disturbed sites where rates of transport are likely to be greatest. Until recently, few measurements have been made of aeolian sediment transport over multiple wind events and across a variety of types of dryland ecosystems. To evaluate potential trends in aeolian sediment transport as a function of woody plant cover, estimates of aeolian sediment transport from recently published studies, in concert with rates from four additional locations (two grassland and two woodland sites), are reported here. The synthesis of these reports leads to the development of a new conceptual framework for aeolian sediment transport in dryland ecosystems along the grassland–forest continuum. The findings suggest that: (1) for relatively undisturbed ecosystems, shrublands have inherently greater aeolian sediment transport because of wake interference flow associated with intermediate levels of density and spacing of woody plants; and (2) for disturbed ecosystems, the upper bound for aeolian sediment transport decreases as a function of increasing amounts of woody plant cover because of the effects of the height and density of the canopy on airflow patterns and ground cover associated with woody plant cover. Consequently, aeolian sediment transport following disturbance spans the largest range of rates in grasslands and associated systems with no woody plants (e.g., agricultural fields), an intermediate range in shrublands, and a relatively small range in woodlands and forests. These trends are consistent with previous observations relating large rates of wind erosion to intermediate values for spatial density of roughness elements. The framework for aeolian sediment transport, which is also relevant to dust fluxes, wind erosion, and related aeolian processes, is applicable to a diverse suite of environmental challenges, including land degradation and desertification, dust storms, contaminant transport, and alterations of the hydrological cycle.

Influence of bed material size heterogeneity on bedload transport uncertainty

The bed material grain size distribution of gravel bed streams is often spatially heterogeneous. The heterogeneity is actually a random parameter, even for a “well‐mixed mixture,” which potentially causes the transport rate for a given bed material to become an uncertain variable. The cause of bed material heterogeneity is the nonuniformity of the bed material, which is analyzed in this paper using examples from field observations and experimental data. The Monte Carlo simulation method is applied to study the uncertainty of the bedload transport rate using Wilcock's experimental data (P. R. Wilcock et al., 2001; P. R. Wilcock and J. C. Crowe, 2003). Each realization of the Monte Carlo simulation employed a randomly generated grain size distribution field for the entire simulation domain. With sufficient realizations the simulation results were adequate to show that the transport rates were a random variable and the mean transport rates did not fall on a single‐valued curve when the local heterogeneity was taken into account. The results indicate that the bedload transport rate of nonuniform sediment has an intrinsic uncertainty that can result solely from the bed material. The results also partially account for the scatter of the fractional transport rate within Wilcock's experimental data. This study presents an important concept in understanding the uncertainty associated with estimates of sediment transport.

Sediment threshold under stream flow: A state-of-the-art review

The doctoral research of Albert Frank Shields on sediment movement conducted in Technischen Hochshcule Berlin becomes a legend that is most often referred by many authors and has initiated a sizable number of researches over last seven decades. The Shields diagram is famous due to its application in ascertaining the threshold of sediment motion that is an essential prerequisite for the estimation of sediment transport in an alluvial stream. Since his pioneering work, numerous attempts have so far been made to study the sediment threshold both experimentally and theoretically. This paper presents a comprehensive state-of-the-art review of the important laboratory experimental and theoretical investigations on sediment threshold under steady stream flow highlighting the empirical concepts, hydrodynamic background and the mathematical treatment of the problem. The role of the turbulent bursting on sediment threshold is also discussed.

The effect of bedform dynamics on computing suspended sediment fluxes using optical backscatter sensors and current meters

The sensitivity of the suspended sediment flux is tested with respect to rapid changes in bed-level across the surf zone of a sandy beach. The suspended flux was computed using a fixed instrument array, but bed-level changes due to ripple migration caused the instrument elevations to be significantly changed during the course of the experiment. The nominal elevations of the instruments were adjusted during data processing (using the MOBS array) to maintain a fixed elevation with respect to bed-level changes. The resultant suspended sediment concentrations and fluxes were significantly different from the unadjusted data, and for the present data set O(35%) less when averaged over the tide. The maximum difference between adjusted and unadjusted fluxes may be O(260%). The results indicate that changes in bed-level, particularly those due to bedform migration, must be accounted for when processing OBS data if reliable estimates of suspended sediment transport are to be obtained in the field.

Breaching Timescales and Peak Outflows for Perched, Temporary Open Estuaries

Intermittent breaching of sand barriers at temporary open estuaries plays a key role in the functioning of these systems. In addition to their ecological impacts, breaching events can cause significant morphological changes because high breach outflows result in the scouring of significant amounts of accumulated sediments from an estuary. Estimation and modeling of these processes requires insight into the parameters that determine features of the breach such as its size and the timescales for the breach formation. The latter is particularly important for characterizing the outflow hydrograph and for estimating sediment transport effects. Simple laboratory experiments are reported that investigated the temporal evolution of the breach and the scaling of the breach formation time TF and peak outflow QP . The experiments were specifically designed to investigate the influence of the outflow volume S, the hydraulic head H, and the barrier breadth B. A scaling is suggested that gives a good description of the experimental data. The scaling is shown to be consistent with observed breach characteristics for actual estuaries (or coastal lagoons) and earth-dam failures where outflow volumes are several orders of magnitude larger than the models.

Monitoring and modelling particle and reach-scale morphological change in gravel-bed rivers: Applications and challenges

This paper focuses on developments in topographic data acquisition, including airborne remote sensing, digital photogrammetry, differential GPS, and laser profiling (e.g. LiDAR) technologies that allow rapid acquisition of high resolution and high precision topographic data sets over a range of spatial scales. These developments have offered new opportunities for investigating spatial and temporal patterns of morphological change in gravel-bed rivers and have contributed to revitalization in three key areas: (1) morphometric estimates of sediment transport and sediment budgeting; (2) boundary conditions for numerical models, including computational fluid dynamics and cellular modelling; (3) three dimensional characterisation of morphology that is independent of flow stage. The potential is clear but there remain a number of significant challenges, including quality control and the effects of error on specific applications and morphologies. This paper presents results from two investigations, representing field and laboratory analyses of gravel-bed river morphology at different spatial scales and for different applications. Case study 1 is concerned with monitoring and modelling morphological change in a large, braided gravel-bed river, using ground-based GPS survey and digital photogrammetry derived from airborne imagery. Case study 2 is an investigation of the mechanisms for infiltration of fine sediment into gravel-bed rivers, which applies close range laser altimetry in flume experiments to derive very high resolution digital elevation models (DEMs) that are used to quantify and analyse changes in bed texture. These case studies highlight the strengths and weaknesses of specific technologies and approaches to analysis of channel and floodplain morphology and change, and suggest key areas that remain to be fully resolved. In particular, the critical need to define a specific threshold level of detection associated with each acquisition method, and for different fluvial settings (e.g. bar surface, sub-aqueous zone), is emphasised.

A study of the deltaic coast morphometry of river Pinios in relation to its hydro- & sediment dynamics

This paper refers to the study of the morphodynamic processes, on a seasonal basis, in the river delta of Pinios (Greece) with the application of the discharge effectiveness index (Ef) -which associates the water discharge (D) with the wave power (PJ- and the estimation of the potential longshore sediment transport (Ql). The delta is characterised according to the classification proposed by Galloway (1975) and revised by Briggs et al (1997), as wave/fluvial dominated type of delta, having a cuspate shape like the deltas of San Francisco and Rhone. Wave processes are dominant during summer-autumn period (low values ofEf) and river processes are important in winter and spring (high values ofEf). The total potential longshore sediment transport is northwards and more intensive in the region to the south of its current mouth.

Long-period Waves and Associated Flows near River Mouth and Narrow Inlet

In order to estimate sediment transport near a river mouth and a narrow inlet, it may be important to investigate the behavior of the long-period waves with periods of several minutes generated by wave groups in the sea. In this study, characteristics of the long-period waves and associated flows near Tenryu river mouth and the inlet of Hamana Lake are discussed based on the field data. Long-period waves are developed almost linearly to both significant wave heights and periods outside the inlet, but they are reduced about half in the inlet. The long-period fluctuation in the flow seems to consist of two components; one is associated with the long-period waves and the other is generated by tidal currents.

A remote‐sensing technique for the identification of aeolian fetch distance

AbstractThis paper describes a new method for assessing aeolian fetch distances in beach/dune systems. The remote‐sensing technique has advantages over currently used proxy measures of fetch distance, such as those based on tide gauges and beach profiles. The method uses a digital camera, global positioning system surveying, and a geographical information system software package to produce a rectified image of the beach surface. From this, direct measurements of the wet–dry beach boundary can be combined with wind direction measurements to determine fetch distance. The method offers an improvement on current approaches to sediment transport estimates: a 28‐day study on Magilligan Strand, Northern Ireland, showed that the commonly used high water mark approach overestimated fetch distance by 30% compared with the technique reported here.

English

A model of soil erosion and sediment transport on hillslopes is used to illustrate the role of process understanding in determining dominant processes as a function of spatial scale. Erosion and sediment yield from hillslopes are primarily determined by surface runoff, topography, vegetative canopy cover, ground surface cover, soil erodibility, and sediment properties. In areas where winter processes (snow, snowmelt, soil frost, etc.) are important, erosion and sediment yield also determined by these factors. The Hillslope Erosion Model (HEM) incorporates these factors in simulating erosion and sediment yield. The world's largest rainfall simulator database for arid and semiarid areas and data from small hillslope-scale watersheds are used to calibrate and validate the spatially distributed, processed-based HEM. Spatially distributed estimates of sediment transport and yield along hillslopes from the HEM are used with an understanding of dominant processes as a function of spatial scale as the scientific basis to determine stability of slopes at plot to hillslope scales. Interrill processes of raindrop splash and thin sheetflow transport are diffusive. Concentrated flow (rill erosion) processes are advective. Spatial loci of transition from diffusive to advective processes are inherently zones of landscape instability and channel formation. The HEM is used to define these areas of instability on hillslopes. Stability criteria for hillslopes are in turn used as criteria for geomorphic designs. Field data taken on a mine rehabilitation site in Queensland, Australia and at the Yakima Training Center in Washington State were used to extend the erosion model to disturbed site rehabilitation problems. These example applications from natural and designed slopes are used to illustrate model predictions and their applications in scaling and geomorphic designs.