Lagrangian sediment motion in a crescentic nearshore bar under storm-induced waves and currents

1982 ◽  
Vol 19 (3) ◽  
pp. 424-433 ◽  
Author(s):  
Brian Greenwood ◽  
Peter B. Hale
Keyword(s):  
Steady State ◽  
Oscillatory Flow ◽  
Tracer Experiment ◽  
Recurrence Interval ◽  
Sediment Flux ◽  
Frequent Occurrence ◽  
Rip Current ◽  
Fluorescent Tracer ◽  
Storm Waves ◽  
Waves And Currents

A fluorescent tracer experiment, in conjunction with morphological and sedimentological data, demonstrates the Lagrangian sediment flux induced by storm waves and currents in a permanently submerged, outer crescentic nearshore bar system. The steady state bar form (height = 2.6 m, wavelength = 390 m) is maintained in the presence of landward sediment advection under asymmetric oscillatory flow during storm buildup and decay and seaward advection under rip-cell flows at the peak of the storm. The seaward displacement of the bar crest in the areas of the convex seaward crescent reflects transport associated with the rip current, which, though variable in its location through time, is never located over the landward projecting horns. The storm studied had a recurrence interval of approximately 1 month and reworked upwards of 16% of the bar sediments. The sediment flux indentified is therefore associated with an event of frequent occurrence and is most likely the control on both bar form and dynamics of the bar system.

scholarly journals Measuring and modelling the isotopic composition of soil respiration: insights from a grassland tracer experiment

2011 ◽  
Vol 8 (5) ◽  
pp. 1333-1350 ◽  
Author(s):  
U. Gamnitzer ◽  
A. B. Moyes ◽  
D. R. Bowling ◽  
H. Schnyder
Keyword(s):  
Steady State ◽  
Isotopic Composition ◽  
Transport Model ◽  
Tracer Experiment ◽  
Atmospheric Co2 ◽  
Soil Co2 ◽  
Soil Air ◽  
Co2 Transport ◽  
Atmosphere System

Abstract. The carbon isotopic composition (δ13C) of CO2 efflux (δ13Cefflux) from soil is generally interpreted to represent the actual isotopic composition of the respiratory source (δ13CRs). However, soils contain a large CO2 pool in air-filled pores. This pool receives CO2 from belowground respiration and exchanges CO2 with the atmosphere (via diffusion and advection) and the soil liquid phase (via dissolution). Natural or artificial modification of δ13C of atmospheric CO2 (δ13Catm) or δ13CRs causes isotopic disequilibria in the soil-atmosphere system. Such disequilibria generate divergence of δ13Cefflux from δ13CRs (termed "disequilibrium effect"). Here, we use a soil CO2 transport model and data from a 13CO2/12CO2 tracer experiment to quantify the disequilibrium between δ13Cefflux and δ13CRs in ecosystem respiration. The model accounted for diffusion of CO2 in soil air, advection of soil air, dissolution of CO2 in soil water, and belowground and aboveground respiration of both 12CO2 and 13CO2 isotopologues. The tracer data were obtained in a grassland ecosystem exposed to a δ13Catm of −46.9 ‰ during daytime for 2 weeks. Nighttime δ13Cefflux from the ecosystem was estimated with three independent methods: a laboratory-based cuvette system, in-situ steady-state open chambers, and in-situ closed chambers. Earlier work has shown that the δ13Cefflux measurements of the laboratory-based and steady-state systems were consistent, and likely reflected δ13CRs. Conversely, the δ13Cefflux measured using the closed chamber technique differed from these by −11.2 ‰. Most of this disequilibrium effect (9.5 ‰) was predicted by the CO2 transport model. Isotopic disequilibria in the soil-chamber system were introduced by changing δ13Catm in the chamber headspace at the onset of the measurements. When dissolution was excluded, the simulated disequilibrium effect was only 3.6 ‰. Dissolution delayed the isotopic equilibration between soil CO2 and the atmosphere, as the storage capacity for labelled CO2 in water-filled soil pores was 18 times that of soil air. These mechanisms are potentially relevant for many studies of δ13CRs in soils and ecosystems, including FACE experiments and chamber studies in natural conditions. Isotopic disequilibria in the soil-atmosphere system may result from temporal variation in δ13CRs or diurnal changes in the mole fraction and δ13C of atmospheric CO2. Dissolution effects are most important under alkaline conditions.

scholarly journals ONSHORE-OFFSHORE SEDIMENT MOVEMENT ON A BEACH

1978 ◽  
Vol 1 (16) ◽  
pp. 87 ◽  
Author(s):  
P. Nielsen ◽  
I.A. Svensen ◽  
C. Staub
Keyword(s):  
Experimental Data ◽  
Diffusion Coefficient ◽  
Oscillatory Flow ◽  
Sediment Flux ◽  
Three Dimensions ◽  
Two Dimensional ◽  
Present Formulation ◽  
Exact Analytical Solutions ◽  
Net Flux ◽  
Loose Sediments

A theoretical model is developed for the movement of loose sediments in oscillatory flow with or without a net current. In the present formulation the model is two-dimensional, but may readily be extended to three dimensions. It is assumed that all movement of sediments occurs in suspension, and exact analytical solutions are given for the time variation of the concentration profile, the instantaneous sediment flux and the net flux of sediment over a wave period. The model requires as empirical input a diffusion coefficient e and pick-up function p(t), for which experimental data are presented. Two examples are discussed in detail, illustrating important aspects of the onshore-offshore sediment motion.

Sphenothallus-like fossils from the Martinsburg Formation (Upper Ordovician), Tennessee, USA

2011 ◽  
Vol 85 (2) ◽  
pp. 353-359 ◽  
Author(s):  
Maya Li Wei-Haas ◽  
Bosiljka Glumac ◽  
H. Allen Curran
Keyword(s):  
Marine Invertebrate ◽  
Limited Evidence ◽  
Upper Ordovician ◽  
Shallow Marine ◽  
Storm Waves ◽  
Waves And Currents

Tubular fossils, up to 2 mm in diameter and 60 mm in length, occur rarely in the upper Martinsburg Formation (Upper Ordovician), northeastern Tennessee Appalachians, U.S.A. The fossils are unbranched, straight or slightly bent, occasionally twisted and wrinkled, and not significantly tapered. Orientation of the fossils within shallow-marine tempestites suggests that they represent remains of organisms that were broken, transported, and deposited by storm waves and currents. The fossils are morphologically similar to many of the previously identified species belonging to the genus Sphenothallus, a relatively rare tube-dwelling Paleozoic marine invertebrate. Owing to the limited evidence for distal widening of the tubes, lack of holdfasts, and carbonaceous rather than phosphatic composition, the affinity of these fossils remains uncertain, and we refer to them as Sphenothallus-like.

2D Experimental Study of Waves and Current Contribution to the Nearbed Velocities and Shear Stresses Field

2004 ◽  
Author(s):  
M. R. Delgado Blanco ◽  
T. De Mulder ◽  
M. Willems ◽  
R. Banasiak ◽  
R. Verhoeven ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Field Data ◽  
Oscillatory Flow ◽  
Roughness Length ◽  
Numerical Models ◽  
Shear Stresses ◽  
Friction Forces ◽  
Current Contribution ◽  
Laboratory Flume ◽  
Waves And Currents

Most of what is known about flow under waves and currents has been deduced from numerical models and not always validated. Absence of accurate experimental and field data, including measurements within the boundary layer or in its vicinity, makes the observation and study of the interaction between steady and oscillatory flow together with model validation difficult. A series of 2D experiments has been done in a laboratory flume. Velocity profiles obtained under different conditions have been analyzed. In addition, a simple 1DV model for turbulent boundary layer simulation has been used. Computed near bed velocities and roughness length are compared with experimental results. By means of three methods based on experimental and numerical results, variations of friction forces as a result of the interaction between the oscillatory and the steady components are evaluated.

Seiche-induced resuspension in Lake Kinneret: A fluorescent tracer experiment

1997 ◽  
Vol 99 (1-4) ◽  
pp. 123-131 ◽  
Author(s):  
B. Shteinman ◽  
W. Eckert ◽  
S. Kaganowsky ◽  
T. Zohary
Keyword(s):  
Tracer Experiment ◽  
Lake Kinneret ◽  
Fluorescent Tracer

scholarly journals Measuring and modelling the isotopic composition of soil respiration: insights from a grassland tracer experiment

2011 ◽  
Vol 8 (1) ◽  
pp. 83-119 ◽  
Author(s):  
U. Gamnitzer ◽  
A. B. Moyes ◽  
D. R. Bowling ◽  
H. Schnyder
Keyword(s):  
Steady State ◽  
Isotopic Composition ◽  
Transport Model ◽  
Tracer Experiment ◽  
Atmospheric Co2 ◽  
Soil Co2 ◽  
Soil Air ◽  
Co2 Transport ◽  
Atmosphere System

Abstract. The carbon isotopic composition (δ13C) of CO2 efflux (δefflux) in ecosystems is generally interpreted to represent the actual isotopic composition of respiration (δresp). However, soils contain a large CO2 pool in air-filled pores. This pool receives CO2 from belowground respiration and exchanges CO2 with the atmosphere (via diffusion and advection) and the soil liquid phase (via dissolution). Natural or artificial modification of δ13C of atmospheric CO2 (δatm) or δresp causes isotopic disequilibria in the soil-atmosphere system. Such disequilibria generate divergence of δefflux from δresp (termed disequilibrium effect). Here, we use a soil CO2 transport model and data from a 13CO2/12CO2 tracer experiment to quantify the disequilibrium between δefflux and δresp. The model accounted for diffusion of CO2 in soil air, advection of soil air, dissolution of CO2 in soil water, belowground and aboveground respiration of both 12CO2 and 13CO2 isotopologues. The tracer data were obtained in a grassland ecosystem exposed to a δatm of −46.9‰ during daytime for 2 weeks. Nighttime δefflux from the ecosystem was estimated with three independent methods: a laboratory-based cuvette system, in-situ steady-state open chambers, and in-situ closed chambers. The δefflux measurements of the laboratory-based and steady-state systems were consistent, and likely reflected δresp (see Gamnitzer et al., 2009). Conversely, the δefflux measured using the closed chamber technique differed from these by −11.2‰. Most of this disequilibrium effect (9.5‰) was predicted by the CO2 transport model. Isotopic disequilibria in the soil-chamber system were introduced by changing δatm in the chamber headspace at the onset of the measurements. When dissolution was excluded, the simulated disequilibrium effect was only 3.6‰. Dissolution delayed the isotopic equilibration between soil CO2 and the atmosphere, as the storage capacity for labelled CO2 in water-filled soil pores was 18 times that of soil air. These mechanisms are potentially relevant for many studies of δresp in soils and ecosystems, including FACE experiments and chamber studies in natural conditions. Isotopic disequilibria in the soil-atmosphere system may result from temporal variation in δresp or diurnal changes in the mole fraction and δ13C of atmospheric CO2. Dissolution effects are most important under alkaline conditions.

Hydrodynamics of wave-current interaction at a right angle over rough beds

2021 ◽  
Author(s):  
Massimiliano Marino ◽  
Carla Faraci ◽  
Rosaria Ester Musumeci
Keyword(s):  
Shear Stress ◽  
Oscillatory Flow ◽  
Flow Analysis ◽  
Mean Flow ◽  
Gravel Bed ◽  
Combined Flow ◽  
Waves And Currents ◽  
The Mean ◽  
Rough Beds ◽  
The Waves

<p>In the present work, an investigation on the hydrodynamics of waves and currents interacting at right angle over rough beds has been carried out. The work focuses on the effects of wave motion superposed on the current steady boundary layer, and on how the oscillatory flow affects the current velocity distribution, in the presence of gravel and sand beds.</p><p>A laboratory experimental campaign on wave-current orthogonal interaction has been carried out in a shallow water basin at DHI Water and Environment (Hørsholm, Denmark).</p><p>Mean flow has been investigated by computing time- and space-averaged velocity profiles. Friction velocity and equivalent roughness have been inferred from the velocity profiles by best fit technique, in order to measure the shear stress experienced by the current mean flow.</p><p>Tests in the presence of only current, only waves and combined flow have been performed.</p><p>Instantaneous velocities have been Reynolds-averaged to obtain turbulent fluctuations time series and compute turbulence related quantities, such as turbulence intensities and Reynolds stresses.</p><p>The analysis of the mean flow revealed a complex interaction of the waves and currents combined flow. Depending on the relative strength of the current with respect to the waves, the superposition of the oscillatory flow may determine an increase or a decrease of the bottom friction experienced by the current.</p><p>The superposition of waves always induces an increase of turbulence intensity, except over gravel bed in which a decrease is observed in the very proximity of the bottom. Over gravel bed, the presence of the oscillatory flow determines a decrease of the turbulent intensity gradient, which may be related to the decrease of bottom friction observed in the mean flow analysis.</p><p>A turbulence quadrant analysis has been performed and showed that, in the presence of a lone current over a flat gravel bed, the turbulent ejection-sweep mechanism reaches parts of the water column closer to the water surface, similar to what has been observed in the turbulence intensity profiles.</p><p>The superposition of the oscillatory flow appears to induce an increment of ejections and sweeps intensity, which is associated with the shear stress increase at the bottom observed in the mean flow analysis. Moreover, a decrease of the number of ejection and sweep events has been recorded, which suggests a suppression of the ejection-sweep events alongside an enhancement of their intensity.</p>

Steady-state valley width revealed by alluvial terrace sequences

2021 ◽  
Author(s):  
Stefanie Tofelde ◽  
Aaron Bufe ◽  
Jens M. Turowski
Keyword(s):  
Steady State ◽  
Water Discharge ◽  
Full Range ◽  
River Sediments ◽  
Sediment Flux ◽  
Alluvial Terrace ◽  
Valley Bottom ◽  
Fluvial Terrace ◽  
Quaternary Climate ◽  
Lateral Erosion

<div> <p>Lateral erosion by rivers drives valley widening and controls valley-bottom width. The current lack of a comprehensive valley-widening model complicates the reproduction of the full range of valley shapes that we find in nature as well as the prediction of valley evolution under different climatic and tectonic boundary conditions. Field data have shown that water discharge and valley wall lithology control lateral erosion rates. However, order-of magnitude variations in valley width formed in uniform lithology and under similar discharge conditions suggest additional, so far unquantified controls on valley width.</p> <p>Fluvial terrace sequences offer an opportunity to study valley-width evolution under comparable discharge and lithologic conditions. Alluvial terraces are composed of flat surfaces and steep walls carved into previously deposited river sediments. They form where a river alternates between phases of lateral valley widening by lateral planation and vertical incision and terrace formation. In order to form an entire terrace staircase, such alternations have to repeat and many Quaternary terrace staircases are interpreted to be driven by cyclic climate changes. Because Quaternary climate cycles have had comparable amplitudes and durations, individual surfaces in paired climate-driven terrace sequences preserve the widths of valleys that have formed under similar discharge conditions, lithologies and over comparable time-intervals. We use a global compilation of 16 climatically formed alluvial terrace sequences to investigate controls on valley width.</p> <p>Between 90 and 99% of the variance in valley width can be explained by a linear relationship of the width with the total valley depth. Hence, at least one of the missing controls on valley width must scale (close to) linearly with valley depth. Ruling-out a preservation bias and a number of parameters that are unrelated to valley depth, we propose a model that relates valley width to a competition between the sediment supplied from valley walls and the river’s capacity to rework sediment, such that a lateral sediment-flux steady state is reached. According to our model the valley width-depth relationship is controlled by (1) the horizontal hillslope-erosion rate, (2) the lateral sediment-transport capacity of the river and (3) the valley-width which forms in the absence of lateral-sediment input. Hence, the model allows to predict valley width when all of the above parameters are quantified in the field. Alternatively, any of the three parameters can be predicted when valley width is measured. The new model is able to reproduce the first-order trend observed in terrace-derived valley widths and it can explain the evolution of paired terrace sequences, which has so far been a major challenge.</p> </div>

History forces and the unsteady wake of a cylinder

1999 ◽  
Vol 393 ◽  
pp. 99-121 ◽  
Author(s):  
J. R. CHAPLIN
Keyword(s):  
Reynolds Number ◽  
Steady State ◽  
Stokes Equation ◽  
Oscillatory Flow ◽  
Numerical Solutions ◽  
Asymptotic Properties ◽  
Quantitative Agreement ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Unsteady Wake

History forces on a stationary cylinder in arbitrary unsteady rectilinear flow are calculated by means of a model based on the asymptotic properties of the steady-state wake. The results capture many features found in numerical solutions of the Navier–Stokes equation for the same flows, though quantitative agreement deteriorates as the Reynolds number increases over the range 2 to 40. The cases studied are the impulsive start, stop, and reverse, and oscillatory flow.

Forces on the Cognac Platform in Combined Storm Waves and Currents

1989 ◽  
Author(s):  
G.Z. Forristall ◽  
C.A. Gutierrez ◽  
E.G. Ward ◽  
P.W. Marshall
Keyword(s):  
Storm Waves ◽  
Waves And Currents
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