Influence of river pattern and sediment input on estuary morphology

2020 ◽  
Author(s):  
Anne Baar ◽  
Elena Bastianon ◽  
Lisanne Braat ◽  
Daniel Parsons
Keyword(s):  
River Discharge ◽  
Large Scale ◽  
Numerical Models ◽  
Sediment Supply ◽  
Tidal Amplitude ◽  
Model Studies ◽  
Braiding Index ◽  
Sediment Input ◽  
River Pattern

<p>Alluvial estuaries are dynamic landscapes that are very sensitive to changes in boundary conditions such as river discharge and sediment supply. A better understanding of the influence of upstream river discharge and sediment input on the development of estuaries under various scenarios requires long-term morphodynamic models, to both predict future changes and improve geological interpretations by storing the stratigraphy. Past 1D model studies have shown that upstream river discharge has a significant effect on the equilibrium bed profile of estuaries, but these studies ignore the effect of 2D bar and channel formation. Using 2D numerical models to predict the development of these systems on the scale of millennia proved to be difficult, since the modelled morphology is very sensitive to the choice in e.g. sediment transport predictor and bed slope effect. In this study, we use the knowledge of previous research that determined best parameter settings for realistic river and bar patterns to model long-term and large-scale estuary morphodynamics in Delft3D. Our objective is to quantify the effects of river discharge and sediment supply on the shape of estuaries and its deposits. Firstly, we systematically varied upstream river width and tidal amplitude to examine the relation between upstream river pattern and estuary dimensions. We quantified e.g. braiding index, bar dimensions, and tidal excursion length. Results show that flood flow velocities and tidal prism are less influenced by river discharge than suggested by 1D models, and are significantly influenced by the braiding index of the river. With relatively high tides, estuary bar patterns depend on tidal amplitude, while with lower tides estuary depth and braiding index are related to upstream river width and discharge. Next steps will include varying discharge to study the effect on the rate of adaptation of the river and estuary, and varying the grain size of the sediment input at the upstream boundary. We will input coarse sediment to explore differences between fluvial deposits and tidal currents, and fine sediment to use the model for research related to biofilm.</p>

scholarly journals Sediment Supply Explains Long‐Term and Large‐Scale Patterns in Salt Marsh Lateral Expansion and Erosion

2019 ◽  
Vol 46 (20) ◽  
pp. 11178-11187 ◽  
Author(s):  
Cai J.T. Ladd ◽  
Mollie F. Duggan‐Edwards ◽  
Tjeerd J. Bouma ◽  
Jordi F. Pagès ◽  
Martin W. Skov
Keyword(s):  
Salt Marsh ◽  
Large Scale ◽  
Sediment Supply ◽  
Lateral Expansion

Modelling creep deformation in floating ice

2003 ◽  
Vol 30 (1) ◽  
pp. 28-41 ◽  
Author(s):  
K van Steenis ◽  
F E Hicks ◽  
T M Hrudey ◽  
S Beltaos
Keyword(s):  
Large Scale ◽  
Field Experiments ◽  
Numerical Models ◽  
Ice Sheet ◽  
Transversely Isotropic ◽  
Element Model ◽  
Ice Cover ◽  
Load Test ◽  
Drilling Rig

The ability to predict the response of an ice sheet to long-term loading is important in many situations. In northern regions, ice sheets have been used as construction platforms, drilling rig platforms, airfields, parking lots, and festival platforms. Numerical models can be used to predict the deflection of an ice sheet over time and, together with a failure criterion based on allowable deflection, can facilitate the safe use of an ice cover under long-term loading situations. In this study, a two-dimensional axisymmetric finite element model was developed to model the behaviour of a homogeneous, transversely isotropic, infinite ice cover under long-term loading. The model was validated using 33 sets of long-term load test data from large-scale field experiments performed on lake, bay, and reservoir ice and was shown to be capable of reliably predicting deflections under a variety of loading scenarios.Key words: bearing capacity of ice, long-term loading, ice platforms.

scholarly journals Sediment input from the São Francisco River bank, Northeast Brazil, under low discharge period

2021 ◽  
Author(s):  
Francisco Sandro Rodrigues Holanda ◽  
Maria Hosana dos Santos ◽  
Janisson Batista de Jesus ◽  
Wadson De Menezes Santos ◽  
Edinaldo De Oliveira Alves Sena ◽  
...  
Keyword(s):  
Suspended Sediment ◽  
River Discharge ◽  
River Channel ◽  
Sediment Supply ◽  
Northeast Brazil ◽  
Sao Francisco River ◽  
Soil Bioengineering ◽  
São Francisco River ◽  
Sediment Input ◽  
Bioengineering Techniques

The objective of this study was to evaluate the input of suspended sediment from the slope toe in the São Francisco River channel, in Northeast Brazil, under different soil bioengineering techniques. Sediments were collected in the years of 2013, 2014 and 2015, in five transects crossing the river channel. Sediment input in the sampling points was higher in the year of 2013, i.e., the year of the highest river discharge. Sediment supply to the river channel for a period of 3 years (2013, 2014 and 2015), was evaluated at 20, 40 and 60% depth, along five different transects (P1= riverbank, P2= beginning of the thalweg, P3= middle of the thalweg, P4= end of the thalweg, and P5 = margin of the side sandybar), oriented by the presence or absence of erosion control techniques (treatments) such as: 1-Natural Vegetated Slope; 2-Vegetated Riprap; 3-Eroded Slope; 4-Live Cribwall and 5-Vetiver grass Contour Line. Sediments input was different in all evaluated transects, and the one identified as Eroded Slope at 20% depth presented the lowest amount of suspended sediment load. There was a decrease in the total amount of suspended sediment in the evaluated periods, probably due to the progressive decrease in the river discharge, and the protection provided by the soil bioengineering techniques.

scholarly journals MODELLING LONG TERM IMPLICATION OF CLIMATE CHANGE PROJECTION ON SHORE MORPHOLOGY OF NORTH NORFOLK, UK, COMBINING TOMAWAC AND SCAPE

2011 ◽  
Vol 1 (32) ◽  
pp. 61 ◽  
Author(s):  
Nicolas Chini ◽  
Peter Stansby ◽  
Mike Walkden ◽  
Jim Hall ◽  
Judith Wolf ◽  
...  
Keyword(s):  
Climate Change ◽  
Global Climate Change ◽  
Large Scale ◽  
Numerical Models ◽  
Global Climate ◽  
Stationary Processes ◽  
Climate Change Projections ◽  
Future Evolution ◽  
The Future

Assessment of nearshore response to climatic change is an important issue for coastal management. To predict potential effects of climate change, a framework of numerical models has been implemented which enables the downscaling of global projections to an eroding coastline, based on TOMAWAC for inshore wave propagation input into SCAPE for shoreline modelling. With this framework, components of which have already been calibrated and validated, a set of consistent global climate change projections is used to estimate the future evolution of an un-engineered coastline. The response of the shoreline is sensitive to the future scenarios, underlying the need for long term large scale offshore conditions to be included in the prediction of non-stationary processes.

scholarly journals Structure of the Pacific Walker Circulation Depicted by the Reanalysis and CMIP6

Atmosphere ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1219
Author(s):  
Emmanuel Olaoluwa Eresanya ◽  
Yuping Guan
Keyword(s):  
Large Scale ◽  
Structural Changes ◽  
Numerical Models ◽  
Walker Circulation ◽  
Future Climate Change ◽  
Western Boundary ◽  
Extreme Caution ◽  
The Pacific ◽  
Mean State

The Pacific Walker circulation (PWC) is one of the most important components of large-scale tropical atmospheric circulations. The PWC and its influences have been studied extensively by numerical models and reanalysis. The newly released ERA5 and NCEP2 are the most widely used reanalysis datasets and serve as benchmarks for evaluation of model simulations. If the results of these datasets differ significantly, this could lead to a bias in projected long-term climate knowledge. For better understanding of future climate change, it is necessary to evaluate PWC reanalysis productions. As a result, we compared the PWC structures between the ERA5 and NCEP2 datasets from month to seasonal time scales. We used the zonal mass streamfunction (ZMS) over the equatorial Pacific to indicate the strength of the PWC. The PWC’s average monthly or seasonal cycle peaks around July. From February to June, the NCEP2 shows a higher PWC intensity, whereas the ERA5 shows greater intensity from July to December. The circulation center in the NCEP2 is generally stronger and wider than in the ERA5. The ERA5, however, revealed that the PWC’s west edge (zero line of ZMS over the western Pacific) had moved 10 degrees westward in comparison to the NCEP2. In addition, we compared the PWC mean state in the reanalysis and CMIP6 models; the mean state vertical structures of the tropical PWC in the CMIP6 multi-model ensemble (MME) are similar to those of the reanalyses in structure but weaker and wider than in the two reanalysis datasets. The PWC is broader in CMIP6, and the western boundary is 7 and 17 degrees farther west than in the ERA5 and NCEP2, respectively. This study suggests that, when using reanalysis datasets to evaluate PWC structural changes in intensity and western edge, extreme caution should be exercised.

scholarly journals Mathematical Model Studies for River Regulatory Measures for the Improvement of Draft in Hoogly Estuary, India

2014 ◽  
Vol 2 ◽  
pp. 1-12 ◽  
Author(s):  
Rajesh P. Dubey ◽  
S. Samarawickrama ◽  
P.P. Gunaratna ◽  
L. Halgahawatta ◽  
K.P.P. Pathirana ◽  
...  
Keyword(s):  
Numerical Models ◽  
Field Investigation ◽  
Hydrodynamic Modelling ◽  
Model Studies ◽  
Bathymetric Data ◽  
Approach Channel ◽  
Regulatory Measures ◽  
Maintenance Dredging ◽  
Mike 21

The Haldia port is situated in the Hooghly estuary, 104 km downstream of Kolkata Port. As a result of high sedimentation, the navigational channel to the Haldia Port is maintained with great amount of dredging (25 MCM per Annum). The paper presents a study carried out to find a solution to improve the channel depth together with minimum maintenance dredging. A desk study was carried out to identify the historical formation of the estuary and the remedial measures implemented in the past. A detailed field investigation was carried out to obtain the relevant data for the calibration of numerical models. 1D (MIKE 11) river hydrodynamic modelling was carried out using the available bathymetric data to supply upstream boundary conditions for the 2D (MIKE 21) and 3D (MIKE 3) numerical models. Number of possible scenarios were tested through MIKE 21 hydrodynamic modelling to select more feasible options. Selected options were further assessed through morphodynamic and 3D hydrodynamic modelling to examine the long term sustainability of the proposed solutions. Finally, the option which comprise of; approach channel through Balari Passage & closure of the Shore Attached Channel was selected as the best option. The selected option was further studied taking navigational aspects, dredging efforts and construction sequence into consideration.

scholarly journals Timescales of chemical equilibrium between the convecting solid mantle and over- and underlying magma oceans

Solid Earth ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 421-437
Author(s):  
Daniela Paz Bolrão ◽  
Maxim D. Ballmer ◽  
Adrien Morison ◽  
Antoine B. Rozel ◽  
Patrick Sanan ◽  
...  
Keyword(s):  
Chemical Equilibrium ◽  
Large Scale ◽  
Numerical Models ◽  
Solid Material ◽  
Fractional Crystallisation ◽  
Chemical Fractionation ◽  
Magma Ocean ◽  
Material Transfer ◽  
Magma Oceans

Abstract. After accretion and formation, terrestrial planets go through at least one magma ocean episode. As the magma ocean crystallises, it creates the first layer of solid rocky mantle. Two different scenarios of magma ocean crystallisation involve that the solid mantle either (1) first appears at the core–mantle boundary and grows upwards or (2) appears at mid-mantle depth and grows in both directions. Regardless of the magma ocean freezing scenario, the composition of the solid mantle and liquid reservoirs continuously change due to fractional crystallisation. This chemical fractionation has important implications for the long-term thermo-chemical evolution of the mantle as well as its present-day dynamics and composition. In this work, we use numerical models to study convection in a solid mantle bounded at one or both boundaries by magma ocean(s) and, in particular, the related consequences for large-scale chemical fractionation. We use a parameterisation of fractional crystallisation of the magma ocean(s) and (re)melting of solid material at the interface between these reservoirs. When these crystallisation and remelting processes are taken into account, convection in the solid mantle occurs readily and is dominated by large wavelengths. Related material transfer across the mantle–magma ocean boundaries promotes chemical equilibrium and prevents extreme enrichment of the last-stage magma ocean (as would otherwise occur due to pure fractional crystallisation). The timescale of equilibration depends on the convective vigour of mantle convection and on the efficiency of material transfer between the solid mantle and magma ocean(s). For Earth, this timescale is comparable to that of magma ocean crystallisation suggested in previous studies (Lebrun et al., 2013), which may explain why the Earth's mantle is rather homogeneous in composition, as supported by geophysical constraints.

scholarly journals LONG TERM BEACH EROSION: MORPHODYNAMIC CASE STUDY IN MONT-ROIG BEACH, SPAIN

2012 ◽  
Vol 1 (33) ◽  
pp. 68
Author(s):  
Jordi Galofré ◽  
Jordi Galofré ◽  
Dolores Ortiz ◽  
Raúl Medina
Keyword(s):  
Coastal Erosion ◽  
Numerical Models ◽  
Anthropogenic Impacts ◽  
Wave Climate ◽  
Sediment Supply ◽  
Beach Erosion ◽  
Classical Analysis ◽  
Morphological Aspects

Long term coastal erosion in beaches induced by long-shore sediment transport is an important aspect to be taken account in beach behavior. If anthropogenic impacts in coastal stretch (harbor, detached breakwaters, lack of sediments from streams and gullies, and urban pressure) interrupting long-shore currents and transport and decreasing sediment supply, the coastal equilibrium disappears. In this paper a case study is shown in order to analyze long term beach behavior in a coastal stretch affected by erosion. After a brief description of morphological aspects, causes and effects that have incidence on the case study area will be shown. General background and coastal works are detailed. The ideas based on a classical analysis of beach behavior are exposed and results obtained from bathymetric analysis and numerical models are showed. Morphology, wave climate, morphodynamics and sediment budget are evaluated and morphodynamic beach behavior is proposed. A diagnosis is made and mitigation proposal for coastal erosion will be proposed.

scholarly journals Hydro- and morphodynamics in curved river reaches – recent results and directions for future research

2013 ◽  
Vol 37 ◽  
pp. 19-25 ◽  
Author(s):  
K. Blanckaert ◽  
G. Constantinescu ◽  
W. Uijttewaal ◽  
Q. Chen
Keyword(s):  
Sediment Transport ◽  
Secondary Flow ◽  
Large Scale ◽  
Numerical Models ◽  
Three Dimensional ◽  
Future Research ◽  
Turbulence Structures ◽  
Outer Bank ◽  
Flow Processes

Abstract. Curved river reaches were investigated as an example of river configurations where three-dimensional processes prevail. Similar processes occur, for example, in confluences and bifurcations, or near hydraulic structures such as bridge piers and abutments. Some important processes were investigated in detail in the laboratory, simulated numerically by means of eddy-resolving techniques, and finally parameterized in long-term and large-scale morphodynamic models. Investigated flow processes include secondary flow, large-scale coherent turbulence structures, shear layers and flow separation at the convex inner bank. Secondary flow causes a redistribution of the flow and a transverse inclination of the riverbed, which favour erosion of the outer bank and meander migration. Secondary flow generates vertical velocities that impinge on the riverbed, and are known to increase the erosive capacity of the flow. Large-scale turbulent coherent structures also increase the sediment entrainment and transport capacity. Both processes are not accounted for in sediment transport formulae, which leads to an underestimation of the bend scour and the erosion of the outer bank. Eddy-resolving numerical models are computationally too expensive to be implemented in long-term and large-scale morphodynamic models. But they provide insight in the flow processes and broaden the investigated parameter space. Results from laboratory experiments and eddy-resolving numerical models were at the basis of the development of a new parameterization without curvature restrictions of secondary flow effects, which is applicable in long-term and large-scale morphodynamic models. It also led to the development of a new engineering technique to modify the flow and the bed morphology by means of an air-bubble screen. The rising air bubbles generate secondary flow, which redistributes the patterns of flow, boundary shear stress and sediment transport.

scholarly journals SEPARATION OF CLIMATIC FLUCTUATIONS AND IMPACTS OF ENGINEERING ACTIVITIES IN ESTUARIES

1980 ◽  
Vol 1 (17) ◽  
pp. 138
Author(s):  
G. Krause
Keyword(s):  
Water Level ◽  
River Discharge ◽  
Large Scale ◽  
Ocean Basin ◽  
Salt Flux ◽  
Mixing Processes ◽  
Climatic Fluctuations ◽  
Adequate Sampling ◽  
Long Time

Using salinity as an example of dissolved substances in estuarine waters it is shown how the long term trend of concentrations can be split up into a man-made and a climatic contribution. The understanding of long term mixing processes and adequate sampling techniques are essential for this purpose. The physical state of the estuary can be described in terms of 3 basic variables, the river discharge, the filtered water level and the filtered salinity. The river discharge represents the climatic fluctuations in the catchment area, and the filtered water level is a record of the large scale weather pattern over the adjacent ocean basin. Salinity trends which cannot be attributed to these two variables must originate from man-made actions, such as dredging or other engineering activities which change the geometry of an estuary. Two models are used for the trend analysis, the simplest possible mixing equation (which always holds for a sufficiently long time scale), and a salt flux consideration.

Sign in / Sign up

Export Citation Format

Share Document