Tutorial Module07

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Tutorial Description

The TUFLOW Sediment Transport Module is a flexible and powerful bed load and suspended load sediment transport model that enables the 2D/3D simulation of sediment transport in rivers, estuaries and coastal environments. One-or-more sediment fractions can be simulated as they are distributed within the bed and transported as bed or suspended load. This fraction-based implementation allows a high level of control over sediment characteristics. For example, within a single model run, sediment fraction groups can be assigned as cohesive or non-cohesive and there is flexibility to select from a range of common sediment transport models/equations independently for each fraction. The sediment transport module is driven by the TUFLOW FV hydrodynamic model for 2D and 3D flow.

The tutorial will cover a number of aspects of the Sediment Transport model:

  • Represent Suspended Sediment Input and Deposition
  • Representing Suspended Sediment Erosion
  • Bed Load and Additional Sediment Fractions
  • Bed Layering and Bed Armouring
  • 3D Sediment Transport Modelling

    Tutorial Module Data Download

    The tutorial data from which to work from, as well as a set of completed model files should be downloaded from the following page.

    Tutorial Pre-Requisites

    For the purposes of the sediment transport tutorial, we'll be using the hydrodynamic model created in Tutorial Module 3 (Floodplain Application) and supplementing with additional information to specify sediment transport.

    This tutorial will build off the FMA2_Hydro_No_Structures_GIS.fvc. This is hydrodynamic only simulation using GIS integration. For the purpose of this tutorial hydraulic structures are omitted.

  • This tutorial is designed for the Windows Operating System and should use the Windows version of TUFLOW FV.
  • The 2020.01 release (or later) of TUFLOW FV should be used.
  • Installation of the TUFLOW Viewer Plugin
  • QGIS 3.14 or later installed via OSGeo4W with NetCDF4. Instructions on how to complete this is provided via the QGIS Setup Page.

    Suspended Sediment Transport and Deposition

    In the first exercise we will create a simple model of sediment transport by adding a suspended sediment input to the model and simulate its passage through the reach. The sediment input will be a fine sediment which will be allowed to deposit based on a settling velocity but no erosion will occur. Please note that the very fine sediment fraction used in this section of the tutorial is for example purposes only. The actual sediment fraction size distribution for this system is likely to be of greater diameter based on review of the flow conditions.

    The existing FMA2_Hydro_No_Structures_GIS.fvc is a complete hydrodynamic model for a river system with its floodplain. It can be run in a hydrodynamic only mode to assess the flow hydrodynamics but as part of this exercise we’ll add some suspended sediment as an upstream boundary to the model and model it’s transfer down the river channel.

    Specifying the TUFLOW FV Model Control Files

    Open the FMA2_Hydro_No_Structures_GIS.fvc and add the include sediment command as follows into the General Parameters block:

    Include Sediment ==  1,0 !(Enabled, Density coupling)
    

    This will ensure that sediment transport is enabled. The second argument allows the coupling of density. We will leave set at 0 which means that water density is not affected by suspended sediment concentration.

    We also need to add diffusivity model commands that affect the mixing and dispersion of suspended sediment concentrations. Add the following commands into the Model Parameters block:

    Scalar mixing model == Smagorinksy!Mixing model for the scalar variables
    Global horizontal scalar diffusivity == 0.5!Smagorinsky Coefficient
    Global horizontal scalar diffusivity limits == 1.0,99999.!min, max [m2/s]
    

    Add the sediment control file command whose content is described in detail within Section 1.5 of the Manual:

    !_________________________________________________________________ 
    !SEDIMENT CONTROL FILE
    Sediment Control File == FMA2_SED_001.fvsed !Add reference to sediment control file
    

    Modify the fvc file by changing the command from referencing the inflows.csv to steady_inflows.csv for boundary 1, and reference the fineSed time-varying data in steady_inflows.csv by adding fineSed to bc_header section. This will result in our flows being in channel and apply a sediment input into our model.

    bc == Q, 1, ..\bc_dbase\steady_inflows.csv !Flow boundary [m3/s]
    bc header == Date,Main_Inflow, fineSed !Column Headings for boundary data
    

    Also change the reference for boundary 3 as below.

    bc == Q, 3, ..\bc_dbase\steady_inflows.csv !Flow boundary [m3/s]
    bc header == Date,Tributary_Inflow !Column Headings for boundary data
    

    Add the following additional output parameters to the xmdf output section. This will allow us to map the bed shear stress, the sediment 1 flux representing our fine sediment, the total suspended sediment, the total deposition, the resulting bed thickness and the total sediment mass within the bed: Taub, SED_1, TSS, DEPOSITION_TOTAL, THICK and BED_MASS_TOTAL

    output == xmdf
    output parameters  == h,v,d,zb, Taub, SED_1, TSS, DEPOSITION_TOTAL, THICK, BED_MASS_TOTAL !Map Output Results Parameters
    

    Save the TUFLOW FV control file as FMA2_SED_001.fvc

    Copy and paste the steady_inflows.csv from the module data folder to the bc_dbase folder.

    Open the steady_inflow.csv file, you’ll see that there is an additional column called fineSed which will provide us with our time-varying input of fine sediment in mg/l.

    Steady inflows.csv.png

    Close the steady_inflows.csv file.

    Specifying the TUFLOW FV Sediment Control Files

    Create a new text file in the Runs folder called FMA2_SED_001.fvsed.

    FMA2 SED 001.fvsed.png

    Open the FMA2_SED_001.fvsed and add the following commands.

    !TIME COMMANDS
    !_________________________________________________________________
    update dt == 300.
    !_________________________________________________________________
    !SIMULATION CONFIG COMMANDS
    Morphological Coupling ==  0  !Turn on/off Morphological Feedback to Hydrodynamics. 1 to enable feedback, 0 to disable.
    Bed roughness model ==  ks  !ks, d50 or vanRijn .
    Bed roughness parameters ==  0.01, 0.01  !Nikuradse Roughness Height ksc (currents), ksw (waves).
    Bed roughness coupling ==  0  !Turn on/off Bed Sediment Feedback to Bed Roughness. 1 to enable feedback, 0 to disable.
    Erosion Depth Limits ==  0.1, 0.2  !Depth to scale Erosion to Zero (<0.1m no erosion, >0.2m full erosion) 
    Deposition Depth Limits ==  0.1, 0.2  !Depth to scale Despoition to Zero (<0.1m no deposition, >0.2m full deposition)
    !_________________________________________________________________
    !SEDIMENT FRACTION COMMANDS
    Fraction ==  fineSed  !Sediment Fraction 1 Name
       d50 ==  0.000005  !Median Sediment Diameter(m)
       particle density ==  2650  !Particle Density (kg/m3)
       Settling model ==  constant  !Settling Model
       settling parameters ==  0.00002  !Settling Velocity (m/s)
       deposition model ==  ws0  !Deposition model
    End Fraction  !End of Sediment Fraction Definition
    !_________________________________________________________________
    !MATERIAL SPECS COMMANDS
    ! Default Bed Sediment properties for materials
    material ==  0 !default material definition
          suspended Load Scale ==  1.0 !Calibration Factor for suspended load
          Layer ==  1 !Begin Layer Definition
                 Dry density ==  1890.!Dry Density of Sediment Fractions(kg/m3)
                 initial mass ==  1000.!Initial mass of sediment fractions  (kg/m2)
          end layer !End layer definition
    end material !End material definition
    
  • Update dt: The timestep in seconds for performing sediment transport model updating (default is every hydrodynamic model timestep). In our example model this has been set to 15 seconds.
  • Morphological Coupling. Set to 1 to enable morphological coupling, 0 to disable. This setting governs whether the variable bed elevation feeds back into the hydrodynamics. Note bed roughness coupling should only be used if the TUFLOW FV .fvc file is using the ks bottom drag model.
  • Bed Roughness Coupling. Set to 1 to enable bed roughness coupling, 0 to disable. This setting governs whether the changing bed material and roughness height (ksa) is fed back to the hydrodynamic model to calculate bed friction terms.
  • Erosion Depth Limits. Erosion rate is limited to 0 if water depth is less than 0.05m. Between, 0.05m and 0.1m, the erosion rate is linearly scaled down. This is used to avoid unreasonable erosion in cells with small depths. This is particularly applicable at the wet-dry interface. Please note this will affect both bed load transport and bed pickup into the water column. This is similar for the deposition depth limit.
  • Fraction. This is the start of a fraction sub-block where the sediment fraction characteristics are defined in what is known as a sediment fraction block.
  • D50. Median grain size of the sediment fraction in metres.
  • Particle Density. Density of the sediment fraction in (kg/m3)
  • Settling Model. Choice of settling model for the sediment fraction. Choice of None, Constant, Flocculation, Flocculationhindered, vanRijn84 and vanRijn04.
  • Settling Parameters. The settling parameters for the chosen settling model. For the constant settling model selected in this instance, this is the constant settling velocity in m/s.
  • Deposition model. Choice of deposition model. Choice of None, ws0 and Krone.
  • Material. This command indicates the beginning of a material sub-block where the sediment properties are spatially distributed by material type. Using a Material of 0 defines the default parameters for the whole model.
  • Suspended Load Scale. Optional scaling factor for suspended load fluxes. May be used as a calibration factor
  • Layer. This command indicates the beginning of a layer block, specifying unique sediment bed properties for cells within bed layer.
  • Dry Density. Bed layer property that defines the dry density of the bed layer in kg/m3 for each sediment fraction.
  • Initial Mass. Assign quantities in kg/m2 for each sediment fraction.

    In this instance we have chosen to model a fine sand with a D50 of 0.000005m (0.005mm). Such a median grain size is not particularly representative of this specific river but provides a good example to show the simulation of suspended sediment. In reality this kind of grain size is indicative of a cohesive sediment fraction. We will change it to something more realistic in the next example. The settling velocity for a grain size of 0.000005m is approximately 0.00002 m/s from van Rijn's 1984 equation.

    Save and close the file.

    Modify the batch file to run the simulation. If you have a compatible GPU card, follow the instructions here to utilise the GPU card to significantly speed up the simulation.

    Once the simulation has started, open the log file and confirm that the sediment parameters are read in correctly. In this exercise we are modelling a sediment input into the model which can also deposit. No erosion is represented within this model and most options are either set as None or default. We will vary these in later exercises.
    FMA2 SED LOG.png

    Suspended Sediment and Deposition Results Analysis

    Open the results in QGIS and view the flow depth results. Note the channel in the north of the model area. The upstream of this channel is the location we have applied the steady input of fine sediment too. The sediment is applied as a boundary at the upstream end of the reach.

    FMA2 SED 001 Depth.jpg

    Select SED_1 in the Result Type in the TUFLOW QGIS Viewer plugin, and animate results. The sediment input is added to the domain and is transported downstream to the outlet with the ocean.

    SED Depo.gif

    The ‘DEPOSTION_TOTAL’ results parameter can be used to map the deposited sediment within the reach. The darker pink areas show areas of increased deposition. You’ll notice increased deposition in the location of the mid-channel and side bars within the model reach.

    FMA2 SED 001 Depo.jpg

    We can use the QGIS TUFLOW Viewer results analysis tools to determine the sediment concentration at a single point, deposition rate, or the change in bed elevation, thickness and mass as a consequence of the deposition.

    FMA001 SED Deposition Plot.gif

    You’ll see that bed thickness, the THICK results type, increases as a consequence of deposition in this model as we are not representing erosion. This change in bed thickness also slightly increases the bed elevation, ZB, in some areas of the model. The thickness of the bed is calculate as the Total quantity of bed mass (kg/m2) in each layer divided by the dry density (kg/m3). The bed mass in layer 1 is 1000kg/m2 and the dry density is 1890kg/m3. The resulting initial bed thickness is therefore 0.53m.

    FMA001 SED Bed Thickness.gif

    Erosion of Suspended Sediment

    In this part of the tutorial, we will now represent bed erosion within the model to allow any deposited fine sediment to also be picked up by the flow. This mechanism is important for fine grain bed sediment which can be entrained by flow to become suspended sediment.

    Modifying the TUFLOW FV Control Files

    Copy and paste the existing FMA2_SED_001.fvsed file and rename as FMA2_SED_002.fvsed.

    In the FMA2_SED_002.fvsed, firstly, we'll change our grain size to something more appropriate for this type of river environment. Change the D50 to 0.0002m and the settling velocity to 0.026m/s

    !SEDIMENT FRACTION COMMANDS
    Fraction ==  fineSed  !Sediment Fraction 1 Name
       d50 ==  0.0002  !Median Sediment Diameter(m)
       particle density ==  2650  !Particle Density (kg/m3)
       Settling model ==  constant  !Settling Model
       settling parameters ==  0.026  !Settling Velocity (m/s)
       deposition model ==  ws0  !Deposition model
    End Fraction  !End of Sediment Fraction Definition
    !_________________________________________________________________
    

    We'll also add the following two commands to the fineSed fraction commands.

    Erosion Model == Mehta	!Choice of Erosion model
    Erosion parameters == 1.7, 0.2, 1.5 !Er, taucr, alpha
    

    These parameters will set the erosion model to the Mehta model (Also known as the Partheniades model) (other options are van Rijn 84 , Soulsby-van Rijn, Bijker, van Rijn04 erosion models, see the TUFLOW FV STM Manual for more details). The Mehta erosion model uses the following shear excess equation to calculate sediment erosion flux:

    Mehta eq.png

    where:
    Er is the erosion rate constant (g/m2s)
    τbcw is combined bed shear stress due to currents and waves (N/m2)
    τce is critical shear stress for erosion (N/m2)
    α is a power coefficient

    In the erosion parameters command, we specify the erosion rate constant, the critical shear stress for the sediment fraction and the alpha coefficient used by the Mehta erosion model.

    Save and close the FMA2_SED_002.fvsed.

    Copy and paste the existing FMA2_SED_001.fvc file and rename as FMA2_SED_002.fvc.

    Update the reference to the sediment control file to reference FMA2_SED_002.fvsed.

    Sediment Control File == .\FMA2_SED_002.fvsed !Add reference to sediment control file
    

    Add PICKUP_TOTAL and NETSEDRATE_TOTAL, to the list of output parameters.

    output parameters == h,v,d,zb, Taub, SED_1, TSS, DEPOSITION_TOTAL, PICKUP_TOTAL, NETSEDRATE_TOTAL  !Map Output Results Parameters
    

    Save and close the FMA2_SED_002.fvc file, update the batch file and run the FMA2_SED_002 simulation.

    Erosion Results Analysis

    Once the simulation has completed, open the results and plot the SED_1 results parameter for both the completed simulations so far. It can be seen that the sediment concentration for the most recent run is significantly higher than that of first simulation where only deposition was present. The river channel has a lot of energy within it and thus the fine sediment we have introduced would by and large be eroded under the flows we have added to the system.

    The Pick Up Rate (PICKUP_TOTAL) results parameter represents the pick up of suspended sediment and is shown in the below figure. Those areas of highest pickup (erosion) are shown in red.

    Pickup rate.jpg

    The net sediment rate total (NETSEDRATE_TOTAL) represents the pick up rate minus the deposition. A positive value represents areas of deposition and a negative value areas of erosion. We can use this to map and identify areas of net deposition and erosion.

    NetSEDRate.png

    The resulting map shows areas of erosion in red and deposition in blue. You can plot the time-series of the bed thickness, the THICK results parameter, to confirm the areas of erosion and deposition with erosion areas showing a reduction in bed thickness and deposition areas an increase.

    Net Sed Rate Map.jpg

    Suspended Sediment Particle Tracking (Optional)

    It is possible to couple the sediment transport functionality with the particle tracking module described in the Tutorial 6. The following page provides a simple example utilising the FMA2_SED_002 model.

    So far we have represented the transport, deposition and erosion of a fine sediment input within our model. The fine sediment model is not particularly representative for a river of this nature which is characterised by coarser sediments which are subject to bedload.

    Bedload Transport and Additional Sediment Fractions

    In this exercise, we will add a second sediment fraction to represent gravel particles within our reach and introduce bed load transport. The assignment of gravel is more representative of the type of channel and flow rates experienced in this system. As such, we should see more a more site appropriate response of this sediment fraction than the example suspended sediment in the first example.

    Copy and paste the existing FMA2_SED_002.fvsed file and rename as FMA2_SED_003.fvsed.

    Next we’ll add an additional sediment fraction to our model to represent the gravel bed present within our reach. In gravel bed rivers with high energy, a significant amount of sediment can move via bedload. Therefore, we need to add a bed load model and bed load parameters to our gravel fraction. In this instance, we will use the Meyer-Peter-Müller-Shimizu model, noting that a range of other options are also available (Meyer_Peter and Müller, Soulsby-Van Rijn, Bijker, Wilcock-Crowe, van Rijn). We will not specify an erosion model or deposition model for this fraction as we expect this sediment fraction to move as bed load only (and not as suspended load).

    Within the FMA2_SED_003.fvsed add the following section to add gravel to our model.

    Fraction == Gravel  !Sediment Fraction 2 Name
      d50 == 0.032  !Median Sediment Diameter(m)
      particle density == 2650  !Particle Density (kg/m3)
      Settling model == constant  !Settling Model (m/s)
      settling parameters == 0.6  !Settling Velocity (m/s)
      Critical stress model == Soulsby  !Critical Shear Stress Model
      Bed load model == MPM_Shimizu  !Bedload Model
      Bed load parameters == 8.0, -1 ,1.5  !Bedload Model Parameters Er, taucr (set to -1 to use Soulsby model and factor outputs by by 1), alpha	 
    End Fraction  !End Fraction Definition
    

    The MPM-Shimizu bedload model uses the following equation:

    MPM Shimuzu.png

    with

    MPM Shimuzu2.png

    Where:

    µs and µk are the static and kinetic friction coefficient (assumed as 0.6 and 0.48, respectively)
    𝜕𝑧⁄𝜕𝑛̂ is the bed slope component perpendicular to bed shear stress direction.
    τ* and τ*c are non-dimensionalised bed shear stress and critical shear stress, respectively

    With the bedload parameters command we specify a bedload factor, the critical shear stress and the alpha parameter. Unlike the suspended sediment model, the Mehta equation, where we specified a user-defined critical shear stress, this time we are using the Soulsby model. The Soulsby model uses an algebraic expression for the Shields curve developed by Soulsby and Whitehouse (1997) which relates the particle size to the critical shear stress. By using a critical shear stress model the shear stress required for incipient motion varies throughout the simulation based on the D50 characteristics particle size on the bed surface.

    We won’t be adding a gravel input into the upstream end of our model in this instance but instead will allow the bed, comprised of a mixture of fine sediments and gravel, to erode and provide a gravel-based sediment input.

    To do this, modify the following commands in the Material Specs Command in the layer 1 sub-block to represent the two sediment fractions with the bulk being sediment fraction 2.

    Dry density == 1890., 1890. !Dry Density of Sediment Fractions(kg/m3)
    Initial mass == 50., 2950. !Initial mass of sediment fractions  (kg/m2)
    

    Finally we’ll set up the model to represent morphological coupling by changing the following command setting to 1. This allows the changing bed elevations, as a consequence of erosion and deposition, to subsequently feedback and influence the hydrodynamics (which in turn will impact sediment transport)

    Morphological Coupling  == 1 !!Turn on/off Morphological Feedback to Hydrodynamics. 1 to enable feedback, 0 to disable.
    

    Save and close the FMA2_SED_003.fvsed

    Copy and paste the existing FMA2_SED_002.fvc file and rename as FMA2_SED_003.fvc.

    Update the reference to the sediment control file to reference FMA2_SED_003.fvsed

    Sediment Control File == .\FMA2_SED_003.fvsed  ! Add reference to sediment control file
    

    Add BEDLOAD_SED_2, BEDLOAD_TOTAL, SUSPLOAD_TOTAL to the list of output parameters.

    output parameters == h,v,d,zb, Taub, SED_1, TSS, DEPOSITION_TOTAL, PICKUP_TOTAL, NETSEDRATE_TOTAL, BEDLOAD_SED_2, BEDLOAD_TOTAL, SUSPLOAD_TOTAL !Map Output Results Parameters
    

    Save and close the FMA2_SED_003.fvc file, update the batch file and run the simulation.

    Bedload Results Analysis

    Once the simulation is complete, open the results in QGIS and investigate the Bedload_Sed_2 results parameter. You’ll see that we have a significant amount of the second sediment which represents gravel subject to bedload that has been eroded from the bed particularly at the beginning of the event at the upstream part of the model where we are applying the inflow. As we have not specified an initial condition for either the flow or the bed composition, as flow initially moves over the bed a significant amount of sediment sorting occurs. After a while the inflow reaches a steady state and the sediment transport rates also smoothen to a more realistic transport rate.

    Bed Sed 2.jpg

    The amount of bedload and suspended sediment transport can be plotted to show the relative contribution of the various components to total sediment loads. As you can see from the below graph the bedload dominates in our simulation.

    Bed Load 2.png

    Compare the results for bed thickness, pickup total and net sedimentation rate between FMA2_SED_002 and FMA2_SED_003 to assess the variation in results as a consequence of adding the additional sediment fraction. You should see an overall increase in bed thickness and on average less bed erosion when bedload is considered. Also compare the hydraulics for the two models, for the bedload, FMA2_SED_003 model we have turned on morphological coupling so this is fed back into the hydraulics.

    Using the Plot Cross-Section/Long Plot from Map Output tool, select bed elevation, ZB and water level, H, and digitize a line across the width of the channel.

    FMA001 SED X section.gif

    This will provide a cross-section showing the bed elevation at the start of the simulation and the bed simulation at the current point in time, ZB. The ZB results can be animated to show the time-varying change in topography (water surface elevation results can also be displayed).

    Bed Layers and Armouring

    We now have a model with an input of fine sediment at the upstream part of our river reach which is able to deposit and re-erode. Our bed is currently made up of gravel only which is subject to bedload transport. So far we have represented a single bed layer with no bed armouring. Bed armouring is an important component which is common in gravel bed rivers such as the one in our reach, and protects fine sediments in the lower part of the bed.

    Copy and paste the existing FMA2_SED_003.fvsed file and rename as FMA2_SED_004.fvsed.

    In the 'Simulation Config Commands' section of the sediment control file add the following command and parameters to allow bed armouring to be represented.

    Armour layer thickness == 0.05, 0.2 !Specify Min and Max Armour Layer Thickness(m)
    

    This command controls the amount of material within the active layer. If the updated active layer thickness is less than the specified minimum, then mass is exchanged from the underlying layers in order to address this shortfall. Otherwise, if the updated active layer thickness is more than the specified maximum value then mass is exchanged to the next layer.

    Bed-Armouring.png

    In the Material Specs Commands, modify the section to now look as follows. This adds two material layers, a default one which we will have a single layer of non-erodible material which will be applied to the floodplain and one to represent the channel which will have two layers comprises of differing ratios of fine sediment and coarser gravels.

    !MATERIAL SPECS COMMANDS
    ! Bed Sediment properties for each material. 
    material == 2,3,4,5,6,7,8,9 ! default material definition
          Suspended Load Scale == 1.0 !Calibration Factor for suspended load
          Layer == 1 !Begin Layer Definition
                !Material 0 specific erosion parameters                   
                Fraction == fineSed 
                      Erosion Parameters == 0.1, 99999., 0.5 !! Never erode.  In this instance there is no erosion of material 0
                end fraction
                !Material 0 specific Bed Load parameters    
                Fraction == Gravel 
                      Bed Load Parameters == 8, 99999., 1.5 !! Bedload Model Parameters. Never erode.
                end fraction
                Dry Density == 1890, 1890 !Dry Density of Sediment Fractions(kg/m3)
          end layer
    end material
    material == 1 ! River material definition
                Suspended Load Scale == 1.0 ! Calibration Factor for suspended load
                Nlayers == 2  !Number of bed layers
                Layer == 1  !Begin Layer Definition
                      Dry density == 1890., 1890  !Dry Density of Sediment Fractions(kg/m3)
                      initial mass == 50., 2950  !Initial mass of sediment fractions (kg/m2)
                end layer !End layer definition
                Layer == 2  !Begin Layer Definition
                      Dry density == 1890.,1890  !Dry Density of Sediment Fractions(kg/m3)
                      initial mass == 1000,1000  !Initial mass of sediment fractions (kg/m2)
                end layer !End layer definition
    end material !End material definition
    

    With the initial mass command we are making a best estimate of the composition of the bed. We will run the model with the steady inflows for a 24 hour period, a period in which we hope to achieve an equilibrium state (in reality this may take much longer). The equilibrium state will be saved as a restart file for subsequent use with an unsteady model run. To save the bed composition, we need to save a restart file within our FMA2_SED_004.fvsed file.

    To do so, add the following command to write a restart file at 12 hour intervals.

    Write restart dt == 12 !Write Restart File Interval (hrs)
    

    Save and close the FMA2_SED_004.fvsed file.

    Copy and paste the existing FMA2_SED_003.fvc file and rename as FMA2_SED_004.fvc.

    Update the reference to the sediment control file to reference FMA2_SED_004.fvsed

    Sediment Control File == .\FMA2_SED_004.fvsed ! Add reference to sediment control file
    

    Add D50_Layer_1, D50_Layer_2 to the list of output parameters. This provides mapped results outputs for the characteristic sediment size in each layer. Also add BED_MASS_LAYER_1_SED_1, BED_MASS_LAYER_1_SED_2, BED_MASS_LAYER_2_SED_1 and BED_MASS_LAYER_2_SED_2, this will add the bed mass in each layer for each sediment fraction. It's the relative composition of these which determine the characteristic sediment size in each layer of the bed.

    output parameters ==  h,v,d,zb, Taub, SED_1, TSS, DEPOSITION_TOTAL, PICKUP_TOTAL, NETSEDRATE_TOTAL, THICK, BED_MASS_TOTAL, PICKUP_TOTAL, NETSEDRATE_TOTAL, 
    BEDLOAD_TOTAL, SUSPLOAD_TOTAL, D50_Layer_1, D50_Layer_2, BED_MASS_LAYER_1_SED_1, BED_MASS_LAYER_1_SED_2, BED_MASS_LAYER_2_SED_1, BED_MASS_LAYER_2_SED_2 !Map Output Results Parameters
    

    Save and close the FMA2_SED_004.fvc file, update the batch file and run the simulation.

    Bed Layers Results Analysis

    Once the simulation is complete, use the QGIS TUFLOW Viewer plugin to investigate the Total bed mass, bed thickness and D50 particle size for the bed layers 1 and 2.

    In areas of erosion the removal of finer sediment, and subsequent bed armouring, leads to an increase in the characteristic bed sediment size in the upper layer.

    Bed D50.png

    In areas of deposition, there is likely to be an increase in the characteristic sediment size in the upper layer as finer material is deposited.

    Generally speaking throughout the model, we have an equilibrium state within the bed mass which can then be used for subsequent simulations. This equilibrium state is a much better representation than the initial estimate of the initial mass and provides a more stable bed sediment regime.

    Using the Bed Restart File

    From the graphs and the Zb parameters, you’ll notice that we achieve some level of equilibrium bed mass from which we can run subsequent simulations on.

    Copy and paste the existing FMA2_SED_004.fvsed file and rename as FMA2_SED_004a.fvsed.

    Remove or comment out the following command:-

    Write restart dt == 12 !Write Restart File Interval (hrs)
    

    Replace with following command to read in the bed composition from the previous run.

    Bed restart file == log\FMA2_SED_004_bed.rst !Read Bed Restart File
    

    Save and close the FMA2_SED_004a.fvsed file.

    Copy and paste the existing FMA2_SED_004.fvc file and rename as FMA2_SED_004a.fvc. Change the reference to the sediment control file to FMA2_SED_004a.fvsed.

    Sediment Control File == .\FMA2_SED_004a.fvsed ! Add reference to sediment control file 
    

    Update the reference in the boundary conditions block to reference the inflows.csv file for both the discharge boundaries. In this instance we will apply an unsteady upstream flow boundary to our model. We will also remove the FineSed input from the model. The boundary conditions block should look as follows.

    ! BOUNDARY CONDITIONS											  
    bc == Q, 1, ..\bc_dbase\inflows.csv ! Flow boundary [m3/s]
      bc header == Date,Main_Inflow ! Header information
    end bc
    bc == WL, 2, ..\bc_dbase\tide.csv ! Water level boundary [m]
      bc header == Date,level	! Header information
    end bc
    bc == Q, 3, ..\bc_dbase\inflows.csv ! Flow boundary [m3/s]
       bc header == Date,Tributary_Inflow ! Header information
    end bc
    bc == WL, 4, ..\bc_dbase\tide.csv ! Water level boundary [m]
      bc header == Date,level	! Header information
    end bc
    

    Save and close the FMA2_SED_004a.fvc file, update the batch file and run the simulation. As the simulation has a greater number of wet elements, the simulation will take a little longer to run.

    Once complete investigate the results using the results parameters shown previously. You’ll see in this instance that the unsteady event is one that extends out of bank on to the floodplain. On the floodplain we get deposition of suspended sediment but no erosion. This is a result of the spatial variation represented by the different material blocks that we added.

    FMA2 SED 004a.jpg

    Investigate the bed mass and the D50 for the various layers, you should see that the starting point reflects the bed restart file and matches the bed mass and layer D50 at the end of the previous simulation. You'll also see how the characteristic sediment size varies between the channel and the floodplain with the channel characterised by coarser gravels and the floodplain by fine grain sediment. As the floodplain bed is set to non-erodible, there is no inputs into the bedload and therefore suspended sediment is dominant. This has an impact upon the bed thickness on the floodplain which is much less than that in the channel.

    3D Sediment Modelling

    Coming Soon

    Summary

    TUFLOW FV has the capability to model sediment transport in both coastal and riverine environments in 2D and 3D. Both suspended sediment and bed load transport can be simulated including support for consolidated and unconsolidated sediments. The sediment transport simulations can be run utilising GPU card technology for significant run time gains whilst the TUFLOW Viewer QGIS plugin provides an excellent tool for the analysis and processing of TUFLOW FV sediment results. The sediment transport functionality within TUFLOW FV can also be used in conjunction with the particle tracking module and the water quality module which are covered in the following tutorials:-