Meshing M02

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Tutorial Description

Read the Tutorial Model Introduction before starting this tutorial. It outlines the required links to download SMS, which we will use for mesh generation.

In this tutorial we will a build mesh for a riverine channel using the Aquaveo SMS. Specifically we will:

• Use the topographic pre-processor TOPAZ to assist in defining the mesh geometry.
• Develop skills for designing an efficient in-channel mesh.

Riverine Channel Project Area

The dimensions of the meandering riverine channel are shown below:

• Channel depths to -7m.
• Length of channel ~2000m.
• Varying width of channel between 60m to 100m.
• Sinuous channel.

Oblique view of the completed model mesh displayed in SMS

Requirements And Downloads

Requirement	Brief Description
Model Data	Download the Meshing Module 2 Data Package.
Assumed Knowledge	It is recommended to complete the Meshing Module 1 prior to completing this tutorial.

Prepare Your Working Environment

Copy and unzip the Model Data to your preferred working location, for example E:\TUFLOWFV\Meshing_M02.

• The Complete_Mesh folder contains a completed version of the tutorial and its supporting files. You can use this as a reference if you require.

• The Module_Data folder contains the required mesh files to complete this tutorial.
• The Working folder is where we will save our files and build our mesh.

Note: All file paths referred to will be relative to this base directory. For example, Complete_Mesh\Riverine_Channel_000 refers to E:\TUFLOWFV\Meshing_M02\Complete_Mesh\Riverine_Channel_000.

Setup Your SMS Project

Before we start meshing, we'll save off a new SMS project and setup our working projection. Launch SMS and the workspace will be as shown below:

Save an empty project as Riverine_Channel_000.sms into your Working folder:

From the menu bar select File > Save As...

Setting The Workspace Projection

From the menu bar select Display > Display Projection....

In the Display Projection dialogue box set Global projection and click Set Projection.

The Horizontal Projection dialogue will appear. In Filter Strings: search WGS 84 UTM zone 60s and under Southern Hemisphere select WGS 84 UTM zone 60 > OK > OK.

Prepare The Bathymetry Data

Load And Visualise Bathymetry Data

From the Module_Data folder open the provided bathymetry scatter dataset RiverBend_Bathymetry.tin in SMS.

To colour the bathymetry select Display > Display Options (or if you prefer, try the ctrl+d keyboard shortcut). In the Scatter option select the Scatter tab > untick Points and Breaklines and > tick Contours.

In the Scatter option select the Contours tab and Color Fill for the Contour Method. Click on the Color Ramp button and Reverse the Palette Preview.

The bathymetry will be displayed as below:

In the Display Options - Scatter tab, tick Triangles to match the display below.

Prepare Bathymetry For TOPAZ Processing

Now that the required datasets are loaded, we can begin to create the model mesh. We will be using to the topographic preprocessor TOPAZ to help guide our mesh development. TOPAZ allows you to extract topographic features from the DEM such as the channel center line and banks. Please note that TOPAZ processing may take some time if using a large dataset.

To run TOPAZ we need to convert the scatter dataset to a Digital Elevation Model (DEM). Right click on the scatter data RiverBend_Bathymetry and select Convert > Scatter -> Raster as shown below:

In the Interpolate to Raster specify the Cell size as 1m and select OK.

Save the new DEM as Working\RiverBend_Bathymetry.tif.

Your workspace should now look similar to the below figure. We have added upstream and downstream labels for your reference.

It's a good idea to regularly save your SMS Project as you work through the tutorial. Select File > Save as… and save the project (ensure the file is being saved as a project file type *.sms). Opening this SMS project file in the future will reload all layers in the project that you have saved.

Defining The Mesh Extent

We will be using the topographic preprocessor TOPAZ to help guide our mesh development. TOPAZ allows you to extract topographic features from the DEM such as the channel center line and banks.

For more examples that use TOPAZ refer to the SMS tutorial Extract Features for Mesh Generation SMS Tutorials.

Right click on the DEM and select Run TOPAZ.

When processing has completed the Info dialog box will appear. Select OK.

Creating The Mesh Centre Line

Rename the default Area Property Map Data layer Centre_Line_PT. This coverage will be used to create a feature point (node) that will be a guide for TOPAZ to generate the channel center line.

Follow the bellow steps to extract the centerline:

1. In the Map Data select Centre_Line_PT.

2. Zoom into the upstream boundary and the feature point tool place a node in a similar location to the example below.

3. Using the Select Object tool right click on the node and select Extract Feature:

4. In the Extract Feature dialog box specify the following:

• Input raster to RiverBend_Bathyetry.tif.
  
• Feature type to Stream.
  
• Output Coverage is set to <Create New> and named Streams. Note: the name Streams is not a requirement and can be changed as you see fit.
  
• Select OK.
  

5. Select the Streams coverage from Map Data. You should see a centerline within your DEM similar to the below:

To be suitable for mesh generation we will need to make some adjustments. However, overall, it makes a good first pass representation of the channel centerline.

Manually Adjusting The Mesh Centre Line

In this section we will adjust the center line to be more 'mesh friendly' by providing the line with a smoother geometry and more regular vertex intervals.

1. To visualise nodes and vertices select Display > Display Options and modify the Map display so that the Point/Nodes and Vertex are checked.

2. At the upstream boundary extend the Streams feature arc to the DEM boundary. Use the Select Feature Point tool to select the end node and drag it towards the upstream boundary. Do not to extend the line beyond the DEM.

3. Using the Select Feature Arc tool select the Streams line and right click selecting Redistribute Vertices.

4. Under Arc Redistribution specify the following:

• Under Specify select Specified spacing.
• Set the Average Spacing to 20m.
• Check Use cubic spline and select OK.

Note: the center line has been smoothed and we have reduced the number of vertices.

Although TOPAZ provided a good first approximation, we need to make some further adjustments of the center line. Using a series of steps and animations as a guide make further amendments to the center line.

Note: that your center line may differ slightly from the below examples depending on how you digitised your node earlier in Centre_Line_PT.

1. Using the Select Feature Vertex tool align the vertices with the deepest section of the channel. Do this for the vertices in the river bend shown in the animation.

2. Move to the midsection of the of the river reach and repeat the process so that the vertices align more consistently with the channel thalweg (the deepest section of the river).

3. Align the center line at the downstream boundary and adjust the end node location. Note: we use the Select Feature Vertex tool for the vertices and the Select Feature Point tool for the end node.

4. Select the center line and right click selecting Redistribute Vertices. Under the Specify select Specified spacing, set the Average Spacing to 20m, check Use cubic spline and select OK.

Creating The Mesh Bank Lines

In this section we will define the left and right overbank locations.

1. Select the Streams coverage. Zoom into the upstream boundary and use the Feature Point tool to place a node in the northwest corner of the bank:

2. Hold down the shift key and use the Select Object tool to select both the new node and channel arc. Right click and select Extract Banks. Use the below information and animation to guide you:

• Input raster as RiverBend_Bathymetry.tif.
• Use the depth this is Closest to Previous.
• Leave Distance from Centerline as the default. If you have a much larger channel you may need to increase this value.
• Output Coverage > Banks <Create New> and name Bank_Lines.
• Leave the remaining options as default and select OK.

Your new coverage Bank_Lines should look similar to the below:

3. Redistribute the vertices along the bank lines using the Select Feature Arc tool and hold the shift key to select both bank lines. Right click and select Redistribute Vertices and specify the following:

• Under Specify select Specified spacing.
• Set the Average Spacing to 20m.
• Check Use cubic spline and select OK.

4. Follow the animations as a guide adjust your bank lines.

This animation provides guidance on aligning the bank lines near the upstream end of the project area.

This animation provides guidance on aligning the bank lines near the downstream end of the project area.

Note: Before moving onto Step 5 make sure you have checked that all of your bank lines are within the DEM extent!

5. Use the below steps and animation to remove the node and combine the banks into the Streams coverage:

• Select the Streams map data layer and delete the node that you created the banks from.
  
• Select the Bank_Lines coverage. Using the Feature Arc tool hold-Shift and select both bank lines, right click and select Copy to Coverage. In the Select Coverage dialog box select Streams and Ok.

Creating Mesh Extent

To produce the final mesh extent the vertices on each bank need to align and Feature Acrs need to be added at the upstream and downstream boundaries to close the mesh extent.

1. In the streams coverage make a note of the ID number for the center line and banks lines. To do this use the Select Feature Arc tool to select each line, and the ID will be displayed at the bottom of the window. See below example:

2. Using the Select Feature Arc tool, select both the left bank and center line (remember to hold down shift to select multiple arcs), right click > Redistribute Vertices.... Specify the following Arc Redistribution parameters:

• Specify set as Source Arc.
• Source Arc set as the center line ID no. (in this example it is Arc 1 but the ID for your center line might be different so check the ID number of your line).
• Target Arc set as the left bank line ID no.(in this example it is Arc 2 but the ID for your left bank line might be different so check the ID number of your line).
• Check Use cubic spline and select OK.
• Now repeat the process for the right bank.

3. We can now remove the center line as it is not needed for the final mesh. Delete the center line using the Select Feature Arc tool select the center line > right click > Delete

Now that the bank lines are finalised we will add feature arcs to the upstream and downstream boundaries to close the mesh extent.

1. Using Create feature Arc tool add an arc perpendicular to the channel at the downstream boundary, making sure you snap the arc to each node at the end of the bank lines. Use the below animation as a guide:

2. Select the arc using the Select Feature Arc tool and right click > Redistribute Vertices....

3. In the Redistribute Vertices dialog box specify the following parameters:

• Specify set as Specified spacing.
• Check both 2nd bias and Use cubic spline.
• Set the average spacing to 5.
• Set the Bias to 4.0.
• Set the 2nd Bias to 4.0.
• Select OK.

4. Repeat Steps 1-3 for the upstream boundary.

Assigning Mesh Type & Elevation Data

Now that the mesh extent is complete we need to apply the elevation data RiverBend_Bathymerty.tin. Use the below steps:

1. From the menu bar select Feature Objects > Build Polygons.

2. Right click on the map data Streams select > Type > Generic > Mesh Generator.

3. Using the select feature polygon tool, select the polygon > right click > select Polygon Attributes.

4. In 2D Mesh Polygon Properties select the following:

• Set the Mesh Type to Patch.
• Set the Elevation (bathy/topo) type to Scatter Set.
• Select the Scatter Options... and the Interpolation dialog will appear.
• Set the Interpolation to Linear.
• Set the Extrapolation to Inverse Distance Weighted.
• Select OK and OK.

Mesh Generation

You are ready to generate your mesh.

Select the Streams map data > right click > select Convert > Map ->2D Mesh and name your new mesh Riverine_Channel_000.

Your mesh should look similar to the below:

Save your new mesh into your Working folder by selecting File > Save As and name it Riverine_Channel_000.2dm. Make sure the Save as type is a 2D Mesh Files (*.2dm).

Congratulations, you have completed the construction of a mesh. Great work!

Feedback

If you have any queries, feedback or requests for new functionality you'd like added to the tutorial modules, please feel free to get in contact with support@tuflow.com.

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Conclusion And Next Steps

Well done on completing Meshing Module 1. You have now learnt how to construct and modify a mesh in SMS using TOPAZ feature extraction techniques.

Return to the Tutorial Introduction Page to complete further meshing and model build tutorials.