Modeling Tidal Stress, Circulation, and Mixing in the Bristol Channel as a Prerequisite for Ecosystem Studies

1983 ◽  
Vol 40 (S1) ◽  
pp. s8-s19 ◽  
Author(s):  
R. J. Uncles
Keyword(s):  
Numerical Model ◽  
Ecosystem Model ◽  
Hydrodynamical Model ◽  
Bed Load ◽  
Sediment Bed ◽  
Tidal Stress ◽  
Horizontal Mixing ◽  
Ecosystem Studies ◽  
Residual Flows ◽  
Model Agreement

A depth-averaged hydrodynamical numerical model is used to evaluate tidal stresses, currents, and mixing in the Bristol Channel and Severn Estuary. Benthic macrofaunal associations and sediment bed types are shown to depend on the magnitude of the tidal stress, and the direction of sediment transport (as bed-load) in the central parts of the Channel is shown to be a consequence of ebb dominated stress. This asymmetry in the tidal stress is mainly caused by M4 currents, and computed M4 elevations and currents are compared with observed values at a number of stations. Residual flows and horizontal mixing are deduced from the hydrodynamical model, and used to construct transport relationships for an ecosystem model. Agreement between observed salinity over a number of years and that computed by the ecosystem model is generally good.Key words: Bristol Channel, hydrodynamical model, salinity model, tidal stress, M4 tides, sediment movement

NUMERICAL MODEL TO SIMULATE THE EROSION ON THE SLOPE DUE TO OVERTOPPING

2010 ◽  
Vol 13 (3) ◽  
pp. 78-87
Author(s):  
Hoai Cong Huynh
Keyword(s):  
Numerical Model ◽  
Flow Model ◽  
Bed Load ◽  
Experiment Data ◽  
Step Method ◽  
Morphological Model ◽  
Load Transport ◽  
Bed Load Transport ◽  
The Finite Difference Method ◽  
Good Agreement

The numerical model is developed consisting of a 1D flow model and the morphological model to simulate the erosion due to the water overtopping. The step method is applied to solve the water surface on the slope and the finite difference method of the modified Lax Scheme is applied for bed change equation. The Meyer-Peter and Muller formulae is used to determine the bed load transport rate. The model is calibrated and verified based on the data in experiment. It is found that the computed results and experiment data are good agreement.

Organic near-bed fluid and particulate transport in combined sewers

1995 ◽  
Vol 31 (7) ◽  
pp. 61-68 ◽  
Author(s):  
E. Ristenpart ◽  
R. M. Ashley ◽  
M. Uhl
Keyword(s):  
Bed Load ◽  
Erosion And Deposition ◽  
Sediment Bed ◽  
Solids Transport ◽  
Particulate Transport ◽  
Sediment Deposits ◽  
Dense Fluid ◽  
Deposition Processes ◽  
Continuous Field ◽  
Heterogeneity Of Solids

Studies in Germany, Belgium, France and Scotland have revealed that there are significant solids transport gradients in the depth of foul and combined sewage flows. Continuous field observations of changes in depths of sediment deposits in combined sewers have also indicated that there is an interaction between the erosion and deposition processes and changes in the mass transport of solids in regions in the overlying flow. A fuller understanding of the interactive phenomena is essential for both sewer sediment management and the minimization of associated pollution from wash-out of solids via CSOs. The paper presents results from the detailed studies in Hildesheim, Germany and those carried out in Dundee, Scotland, investigating the heterogeneity of solids movement with regard to gross solids, erosion of sewer sediments and their interactions with the suspended transport phases and the layer of very dense fluid found to be transported under certain circumstances, near the sediment bed or sewer invert (traditionally called ‘bed-load’).

3D numerical modeling of sediment handling techniques in a hydro power reservoir

2020 ◽  
Author(s):  
Diwash Lal Maskey ◽  
Dipesh Nepal ◽  
Daniel Herman ◽  
Gabriele Gaiti ◽  
Nils Rüther
Keyword(s):  
Numerical Model ◽  
Guide Vane ◽  
Scale Model ◽  
Bed Load ◽  
3D Numerical Modeling ◽  
Deposition Pattern ◽  
Flow Measurements ◽  
Reservoir Volume ◽  
Physical Scale ◽  
3D Numerical Model

<p>Sedimentation of small as well as large water storage reservoir has become a major issue. Due to the fact that we observe a 1% decrease of reservoir volume every year due to sedimentation and that the largest part of the reservoirs have been built between 70 and 40 years ago, many HPPs are confronted with the threatening scenario that soon the active storage and therefore their lifetime is dramatically diminished. Due to the above mentioned combination, active and sustainable sediment management has become the last option to retain or preferable enlarge the left-over reservoir volume. There are several options for a sustainable sediment handling, each for a different boundary condition, which must be evaluated carefully in order to be successful. For a successful choice, design and conduction of a sediment handling technique, usually a physical scale model will be conducted. Physical scale model have the advantage that there is a lot of experience in conducting these models and that they are illustrative. The disadvantage of scale models is that there are restrictions in the use of certain sizes of sediments due to scaling issues and that they are rather expensive.</p><p>This study attempt to use a 3D numerical model to overcome the above mentioned disadvantages and to serve as an additional source of alternatives in finding the right sediment handling techniques in reservoirs with high discharges of suspended and bed load. The goal is to simulate several flood events in order to gain insights in the current situation as well as to have a better understanding of the physical processes in the reservoir. This will support and positive influence the sustainable design of sediment handling techniques. The numerical model will be verified with flow measurements a physical model study and with bathymetry measurements from field observations. Based on the actual deposition pattern and the given input data, different sediment handling techniques are planned and conducted by means of the numerical model. The results show that the 3D numerical model is able to simulate sediment transport deposition pattern, bed load guide vane structures, as well as bed load diversion structures.</p>

scholarly journals Disentangling the effects of climate and people on Sahel vegetation dynamics

2008 ◽  
Vol 5 (4) ◽  
pp. 3045-3067 ◽  
Author(s):  
J. W. Seaquist ◽  
T. Hickler ◽  
L. Eklundh ◽  
J. Ardö ◽  
B. W. Heumann
Keyword(s):  
Data Model ◽  
Land Surface ◽  
Vegetation Dynamics ◽  
Ecosystem Model ◽  
Data Sets ◽  
Aggregated Data ◽  
Human Footprint ◽  
Satellite Sensors ◽  
The 1960S ◽  
Model Agreement

Abstract. The Sahel belt of Africa has been the focus of intensive scientific research since the 1960s, spurred on by the chronic vulnerability of its population to recurring drought and the threat of long-term land degradation. But satellite sensors have recently shown that much of the region has experienced significant increases in photosynthetic activity since the early 1980s, thus re-energizing long-standing debates about the role that people play in shaping land surface status, and thus climate at regional scales. In this paper, we test the hypothesis that people have had a measurable impact on vegetation dynamics in the Sahel for the period 1982–2002. We compare potential natural vegetation dynamics predicted by a process-based ecosystem model with satellite-derived greenness observations, and map the agreement between the two across a geographic grid at a spatial resolution of 0.5°. As aggregated data-model agreement is very good, any local differences between the two could be due to human impact. We then relate this agreement metric to state-of-the-art data sets on demographics, pasture, and cropping. Our findings suggest that demographic and agricultural pressures in the Sahel are unable to account for differences between simulated and observed vegetation dynamics, even for the most densely populated areas. But we do identify a weak, positive correlation between data-model agreement and pasture intensity at the Sahel-wide level. This indicates that herding or grazing does not appreciably affect vegetation dynamics in the region. Either people have not had a significant impact on vegetation dynamics in the Sahel or the identification of a human "footprint" is precluded by inconsistent or subtle vegetation response to complex socio-environmental interactions, and/or limitations in the data used for this study.

scholarly journals A two-dimensional layer-averaged numerical model for turbidity currents

2018 ◽  
Vol 477 (1) ◽  
pp. 439-454 ◽  
Author(s):  
Shihao Yang ◽  
Yi An ◽  
Qingquan Liu
Keyword(s):  
Numerical Model ◽  
Large Scale ◽  
Current Model ◽  
Turbidity Currents ◽  
Two Dimensional ◽  
Dynamic Features ◽  
Field Scale ◽  
Sediment Bed ◽  
Sediment Transportation ◽  
Flow Features

AbstractTurbidity currents occur widely in submarine environments, but field-scale numerical simulations of the flow features have not been applied extensively. Here, we present a two-dimensional layer-averaged numerical model to simulate turbidity currents over an erodible sediment bed, and taking into consideration deposition, entrainment and friction. The numerical model was developed based on the open-source code, Basilisk, ensuring well-balanced and positivity-preserving properties. An adaptive spatial discretization was used, which allows multi-level refinement. The adaptive criterion is based on the dynamic features of the flow and sediment concentrations. The numerical scheme has a relatively high computational efficiency compared with models based on the Cartesian mesh. A hypothetical case based on a true large-scale landform (the Moroccan Turbidite System, offshore NW Africa) was studied. Compared with previous models, the current model accounted for the coupling between flow, sediment transportation and bed evolution. This approach may improve simulation results and also allow the simulation of complex field-scale landforms, while preserving the flow details.

scholarly journals Sediment Bed-Load Transport: A Standardized Notation

Geosciences ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 368
Author(s):  
Ulrich Zanke ◽  
Aron Roland
Keyword(s):  
Shear Stress ◽  
Critical Shear Stress ◽  
Basic Structure ◽  
Structural Formula ◽  
Bed Load ◽  
Viscous Effects ◽  
Data Set ◽  
Sediment Bed ◽  
Load Transport ◽  
Bed Load Transport

Morphodynamic processes on Earth are a result of sediment displacements by the flow of water or the action of wind. An essential part of sediment transport takes place with permanent or intermittent contact with the bed. In the past, numerous approaches for bed-load transport rates have been developed, based on various fundamental ideas. For the user, the question arises which transport function to choose and why just that one. Different transport approaches can be compared based on measured transport rates. However, this method has the disadvantage that any measured data contains inaccuracies that correlate in different ways with the transport functions under comparison. Unequal conditions also exist if the factors of transport functions under test are fitted to parts of the test data set during the development of the function, but others are not. Therefore, a structural formula comparison is made by transferring altogether 13 transport functions into a standardized notation. Although these formulas were developed from different perspectives and with different approaches, it is shown that these approaches lead to essentially the same basic formula for the main variables. These are shear stress and critical shear stress. However, despite the basic structure of these 13 formulas being the same, their coefficients vary significantly. The reason for that variation and the possible effect on the bandwidth of results is identified and discussed. A further result is the finding that not only shear stress affects bed-load transport rates as is expressed by many transport formulas. Transport rates are also significantly affected by the internal friction of the moving sediment as well as by the friction fluid-bed. In the case of not fully rough flow conditions, also viscous effects and thus the Reynolds number becomes of importance.

scholarly journals Impact of the regularity of the sediment bed on bed-load transport

PAMM ◽  
2016 ◽  
Vol 16 (1) ◽  
pp. 583-584
Author(s):  
Ramandeep Jain ◽  
Bernhard Vowinckel ◽  
Jochen Fröhlich
Keyword(s):  
Bed Load ◽  
Sediment Bed ◽  
Load Transport ◽  
Bed Load Transport

Sediment transport in the lower Saginaw River

1995 ◽  
Vol 46 (1) ◽  
pp. 337 ◽  
Author(s):  
M Cardenas ◽  
J Gailani ◽  
CK Zeigler ◽  
W Lick
Keyword(s):  
Sediment Transport ◽  
Transport Model ◽  
Three Dimensional ◽  
Computer Time ◽  
Numerical Calculations ◽  
Time Dependent ◽  
Curvilinear Coordinates ◽  
Bed Load ◽  
Sediment Bed ◽  
Dependent Model

A study of the resuspension, deposition and transport of sediments and the resulting changes in bathymetry in the lower part of the Saginaw River in Michigan has been made. The numerical model used in this study consists of a two-dimensional, vertically integrated, time-dependent hydrodynamic and transport model coupled with a three-dimensional, time-dependent model of the dynamics of the sediment bed and its properties. Transport of sediment as suspended load and bed load was included in the analysis. In the numerical calculations, curvilinear coordinates were used. For verification of the model, results of numerical calculations of changes in the thickness of the sediment bed due to time-varying flow events were compared with bathyrnetric measurements taken at nine transects on the river on 28 August 1991 and 13 May 1992. From the transect measurements, from measurements of flow rates and sediment concentrations, and from the numerical modelling, a reasonably accurate description of the sediment transport and the resulting bathymetric changes has been made. The calculations and observations show that resuspension/deposition, bed load, and slumping are significant factors in changing the bathymetry. It is also shown that the largest flows are responsible for most of the sediment erosion and deposition and must therefore be understood and considered in detail. An approximate procedure for making long-term (1 to 25 year) calculations is presented and discussed. This procedure greatly reduces the required computer time but still maintains the required accuracy for the prediction of sediment and contaminant transport and fate.

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