How to create a TIN

Flood maps are useful for showing the full impact of flooding in models where water encroaches out of bank onto the surrounding floodplain. To Create a Flood Map from 1D river results, you must first prepare these results and create a TIN, as described below.

Prepare Results (in .zzn or .csv format)

A 1D model results file from a model simulation is in a binary format with a zzn file extension (coupled with a zzl file as well). This format is compatible with Flood Modeller and can therefore be uploaded directly. However it is also possible to upload 1D results which have been post-processed to comma separated text format (csv file extension) using the Flood Modeller TabularCSV tool (Results tab). For this latter case your data must have been processed in TabularCSV to the output format 'One Column per Timestep'.

Prepare Results for TIN Creation

The 1D results are associated to particular nodes within your model. In order to display these data on a map the nodes must be geo-referenced within a TIN file.

If a TIN file does not exist for a model, then Flood Modeller can be used to create one. For this procedure, Flood Modeller requires a polyline shapefile to be created where each model node is represented by a cross section (with a minimum of two points, i.e. a point at either end of each section) or polygon (for reservoir units).

There are three main data sources available to obtain this required node information. These are:

1. A 1D model GXY file containing a single point coordinate for each 1D model node
2. A 1D model DAT file (or SEC file) containing all 1D model node data
3. An existing shapefile representing your 1D model cross-sections.
4. An existing shapefile representing your 1D model reservoirs.
   Alternatively, you may already have a TIN file prepared (using another GIS system). In which case you can load this and utilise it directly.
   The different options described above are utilised in Flood Modeller as follows (note in some case you may adopt a combination of these methods depending on availability of data):
5. Import GXY approach- Import a 1D model GXY file and use Flood Modeller to generate geo-referenced cross-sections from this as follows:
   1. Import the GXY file (using the Add GIS Data button under the Home tab). Note that Flood Modeller will import these data as a new point shapefile (you will need to provide a filename for this).
   2. Draw a new shapefile polyline through the points of the GXY file. When editing the shapefile snapping to the gxy node points can be used to ensure the resultant line passes through every point precisely. The snapping control can be accessed under the Layer Editor tab. The new polyline represents a river centre line through the model points.
   3. Click Stop Edit button under the Layer Editor tab to save the new polyline and exit edit mode. With the new centre line highlighted in the Layers panel select the Cross Section Generator from Additional Model Build Tools > 1D Networks in the Toolbox.
   4. Select the appropriate options from the Cross Section Generator window. In particular: ensure that the 'Add cross-section at each point along the shapefile polyline' option is selected; specify an appropriate cross-section length; and reference the gxy points shapefile to provide node labels for each cross section.
   5. Ensure that the cross-sections extend as far as is necessary (to cover the expected flood extent) and that no cross-sections overlap, by using the edit tools to extend, move or rotate selected sections.
   6. Once completed save the cross-section shapefile and use to generate TIN (see point 3).
6. Import 1D model file approach - If a geo-referenced 1D model .DAT or .SEC file, with cross-sections at each node, exists then this can be loaded and used to generate a TIN. The operation requires the sections to be displayed in the map view so first load the .DAT or .SEC file using the standard Add GIS Data function (or drag the network onto the map from your Project panel). Once displayed the 1D model file can be used directly to generate a TIN (see point 3). If the 1D model file has incomplete geo-referencing, then this can be completed by Flood Modeller (providing a valid .GXY file is available with required coordinates for nodes). It should be noted that this approach will only import the river cross section type nodes from your 1D model.
7. Import cross-section approach - If a geo-referenced cross-section generated in an external piece of software exists, this can be imported directly into Flood Modeller. Software such as MDSF produce geo-referenced cross-sections suitable for this approach. Import the cross-section shapefile using the standard Add GIS Data option, then use the shapefile to generate a TIN (see point 3). In order to transfer node names through to a TIN your imported shapefile must have these data in an attribute field entitled ‘label’’.
8. Import reservoir polygons approach - If the main area of interest within a model is overbank flooding, then the floodplain areas may be defined by a series of 'reservoir' polygons. If these data have been geo-referenced as polygon shapefiles, then these data can be imported into Flood Modeller and converted to a TIN in the same way as cross section data (see above). It is also possible to define floodplain reservoirs from within Flood Modeller using the shapefile drawing tools, as described in Layers Editor Tab page of this help file. In order to transfer node names through to a TIN your polygon shapefile must have these data in an attribute field entitled ‘label’.

Create TIN

The next stage is to create a TIN from your cross-section data. If you have generated cross-section polyline or reservoir polygon shapefiles by one of the above approaches, then this must be done using the TIN Creator tool. This is a standalone tool packaged with Flood Modeller (see the TIN Creation tool page for details of how to use). In summary the following describes the TIN creation method using TIN Creator:

1. The TIN Creator tool can be accessed in isolation or from within Flood Modeller. For the latter option access the Layers panel menu by right-clicking on the shapefile layer in the Layers panel, and select Export > To TIN with TIN Creator from the displayed menu. TIN Creator will prompt you for a TIN filename and after this is entered the tool will open with the shapefile automatically loaded. To triangulate click the 'Draw Convex Hull' button and then the 'Triangulate' buttons on the toolbar.
2. Once triangulated the TIN will be shown on the left-hand side of the screen. Triangles within the TIN that are not needed can be deleted by selecting them (holding down the left shift key and selecting as many triangles as required) and hitting delete. In certain circumstances (when cross-sections used to generate the TIN cross over) pseudo-points will be added to the TIN. These points will not have node references, so users will need to refer the pseudo points to two nearby nodes. This is done by left-clicking on the pseudo point, and then left clicking on the relevant nearby node whilst holding down the left control key (to assign the first nearby node) and repeating the process for whilst holding down the left shift key in place of the control key (for the second node). Experience of using pseudo points has shown that they can cause erroneous flood extents, and thus it may be advisable to make sure that cross-sections do not cross over.
3. After completing the triangulation process click on the Flood Modeller icon in the TIN Creator toolbar to upload the new TIN in Flood Modeller with the name specified at the start of the process.

An alternative to using TIN Creator, if you have an 1D network (.dat or .sec format) file loaded (option b above), is to use the Flood Modeller internal triangulation tool. This generates simplified TINs, which only uses the minimum required points rather than all points in each section (e.g. only two points required to describe a straight-line cross-section). The following describes this TIN creation method:

1. The internal TIN generator is run by highlighting your 1D model .DAT or .SEC file in the Layers panel and then selecting 1D Flood Map > Triangulate Selected File from the Modelling Toolbox.
2. You will be prompted to provide a filename for your new TIN and then the file will be produced and added to the Flood Modeller viewport.
3. If you right click on a TIN you can select Start Edit from the displayed menu. This will activate the TIN editing toolbar as an extra tab in the main toolbar. The toolbar provides options to draw new triangles and to remove triangles or points (all associated triangles are then also removed).
4. If new points are added through the drawing of new triangles then you can assign related 1D model node labels to these points by clicking on the Layer Editor toolbar and selecting Attribute Window . This displays a table of all TIN attributes. To assign 1D results you need all Node Label A fields to be populated with valid 1D node names. Edit any cell in the table by double clicking on it and either typing in a node label or adding an existing label from the drop down list displayed below the table (click the adjacent green tick to add a selected label from this list).
5. Remember to save your edited TIN file before you exit the TIN editing mode.

Once created, a TIN can be used to Create a Flood Map, to compare ground levels and water levels to determine if an area is flooded. It is also possible to animate a 1D flood map, with even better results obtained via Animation with the 1D flood map tool.