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19/06/2019 11:05:17

In this month’s tip, we’ll provide some pointers on how best to produce a TIN from a 1D network containing interpolate and/or replicate units. The required start point for this is to ensure your network is fully georeferenced (the user guide provides descriptions of tools to achieve this). We will then describe how to utilise existing Flood Modeller tools for a slightly different purposes to which they were designed in order to generate pseudo sections for each interpolate. These can then be included in your TIN, thus ensuring the water level data calculated for these units is utilised within your flood mapping.

The method for doing this is described as follows:

  1. Use the following steps to create a TIN that includes all replicate and interpolate nodes (and any other nodes you also want to include, i.e. because they have a useful water level to incorporate into a flood map):We are going to utilise the Cross Section Generator tool located in the Toolbox – in Additional Model Build Tools > 1D Cross Sections. This tool requires inputs of a river centre line shapefile and a point shapefile representing the required 1D nodes. These data can be generated by right-clicking on your 1D network in the Project Panel (upper left panel) and selecting the menu options Export > Nodes as Shapefile and Export > Links as Shapefile. Provide suitable names for these files and after they are generated load them into the Layers Panel (lower left panel) so they are added to your map view.Tip of the month - 18/06 - 1
  2. Before we generate cross sections ascertain how long each section (roughly) needs to extend either side of the centreline in order to capture all likely flooding. Also, you need to be aware of extending sections too far so that when a water level is applied in the flood mapping process you don’t create isolated ponds detached from the flooding of the main channel. The measure tool in the map control bar is useful for doing this.Tip of the month - 18/06 - 2
  3. Now open the Cross Section Generator (by double-clicking on it in the Toolbox). It will open in a new window. Complete the settings as detailed below:Tip of the month - 18/06 - 3Tip of the month - 18/06 - 4
  4. Add a suitable filename for the output from the tool. Note the tool creates a “.sec” file which is basically a 1D network file containing only cross sections and no boundaries. Ensure the option to “Add to view” is ticked and then click OK to generate the new section data.
  5. Hopefully the result of this tool will look something like this:Tip of the month - 18/06 - 5The sections created will likely require further editing before proceeding to create a TIN. Common issues are:
    • The tool will only draw sections perpendicular to the given centreline, so where your network is going around a bend it is likely to not get things quite right.
    • The tool draw sections at every node so existing river sections will also get a section drawn for them despite you possibly already having georeferenced data defining the path of these sections.
    • As the tool draws sections for all nodes you will get sections drawn at nodes that don’t need to be part of your TIN, e.g. boundary nodes.

    In these cases, you need to right-click on the sec file in the Layers Panel and select Start Edit. The Layer Editor tab of the main toolbar will be activated. Use the Select tool in this to highlight a section to editTip of the month - 18/06 - 6

    The Rotate tool is operated as shown below. Equally use Delete Selected in the Layer Editor to remove unwanted sections (after using Select to highlight the relevant section).Tip of the month - 18/06 - 7

    For existing river sections you can move individual points in the sec file sections to “trace” the sec file section to match the underlying surveyed section (the Layer Editor includes a snapping function to help get an exact match).

  6. After making all edits Save your changes and click Stop Edit to exit the edit mode.

  7. The resulting sec file can then be converted to a TIN using the tool provided in the Toolbox. To use this, first highlight the sec file in the Layers Panel, then in the Toolbox, in Flood Mapping > 1D Models, double-click on “Triangulate Selected File”. You will be prompted to provide a filename for the new TIN file and after specifying this you are prompted to load the new TIN file into the map view. It should look something like this:Tip of the month - 18/06 - 8

    The TIN should now be ready to associate your 1D results file (zzn file) to it (you can check the TIN attributes to ensure the node labels are correctly presented). The 1D Flood Map tool can then be used to process the TIN, combining it with an appropriate DTM to generate flood depth grids and/or flood extent outlines (details on this tool are provided in the user guide).

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