How to create 1D spill units from a map

This section provides a step by step guide on generating 1D spill units.

Load ground data

A ground grid, i.e. digital elevation model (DEM) from LiDAR data, is required to be loaded into the viewport. This must be a compatible grid format, i.e. binary (flt) or ASCII (asc). On the Home tab, click Add GIS Data and browse to your grid.

The grid provides the vertical elevation data for the spill lines of the new spill units. It should be noted that the ESRI grid format is not compatible for use in spill unit generation. However, the layer convertor tool in Flood Modeller can be used to create a compatible grid from an ESRI grid.

Define spill polylines

If a shapefile of spill polylines already exists then this can be loaded into the viewport. Click on the “Add GIS Data” in the “Home” tab (within “GIS Data” section).

If there is no existing polyline shapefile available that represents the required spill lines then a new shapefile can be defined by drawing directly on the Flood Modeller viewport. On the “Home” tab within the “GIS Data” section click on the “New” button and select “Shapefile” from the drop-down menu. Then select to draw a new polyline shapefile from the presented options. Refer to section How to create a new shapefile for guidance.

Access spill unit function

Click the Spill button in the Map Tools tab of the main toolbar.

Alternatively, from the Toolbox, select:

Additional Model Build Tools / 1D Networks / Run Spill Generator

Specify spill unit parameters

The spill generator will calculate spill levels by analysing elevation data along mini cross-sections drawn across the spill lines at regular intervals. The 1D spill tool requires the following parameters to be set to define this operation:

• The polyline shapefile layer that defines the new spill lines - a list of all loaded polyline shapefiles is provided to select from
• The ground data layer to extract the elevations from – a list of all loaded grids is provided to select from

Search Criteria:

The tool requires the number of mini cross-sections to draw along the spill line in order to define a line of maximum levels. This can be specified by:

1. A spill point (a point where a cross-section will be created) at every point defined within the spill polyline
2. A fixed distance between spill points in metres - Flood Modeller calculates the number of points required along the full length of each spill line
3. A fixed number of spill points - Flood Modeller calculates the constant distance between spill points along the full length of each spill line
   The tool also requires properties of each mini cross-section drawn at each spill point as follows:

• The cross-section length in metres to the left and right of the spill point. These default at 10 metres but can be edited
• The number of points along each cross-section to the left and right of the spill point. These default at 2 points to the left and 2 points to the right of the spill point but can be edited. Note the tool will also calculate the level at the spill point itself, so the default settings calculate the level at 5 points along each cross-section.

The cross-sections, cross-section lines and cross-sections points are saved in separate shapefiles. By default, these are saved to the folder containing the shapefile used to create the spill line. The name of each file is created from a combination of the name of the shapefile used to create the spill line and spillXS, spillLine and spillPoints respectively, separated by an underscore, i.e. my_spill_shapefile_spillXS, my_spill_shapefile_spillLine and my_spill_shapefile_spillPoints. The names and locations of these shapefiles can be edited.

Spill Unit Details:

The spill unit details are accessed via a second tab within the tool interface:

The tool requires 1D node labelling for each spill unit. The table lists the spill nodes and their associated 1D parameters. The upstream and downstream node labels can be entered directly by typing into the appropriate field in the table (double click on the field to enable typing). The weir coefficients and modular limits of individual spill nodes can also be adjusted in this way. Alternatively, the node labels can be automatically filled by clicking on ‘Table Options’ to bring up the following new window:

Spill node labels can be user defined or taken from an attribute field in the polyline shapefile defining the spill lines. Select ‘User Defined’ or ‘Shapefile’ as required via radial button:

• If User Defined is selected:
  The prefix, base value, suffix and increment can all be adjusted manually and a preview of the labelling is shown.
  
• If Shapefile is selected:
  The base value, suffix and increment can be adjusted manually. The prefix can be chosen from a list of available attributes of the polyline shapefile and the preview will appear once one of these has been selected. The preview is particularly helpful for this case as you can ensure the labelling is sensible before applying it.
  
  Navigate to the ‘Downstream’ tab to repeat the procedure and create downstream node labels for the spill nodes. Note you can apply the upstream labels prior to defining the downstream labels, or even apply them and close out of the window, then click ‘Table Options’ again to repeat for the downstream labels.
  
  The weir coefficient and modular limit can be adjusted globally if required (typical values are given by default). Click on ‘Apply’ to apply your chosen labelling to the spill nodes in the table and ‘Close’ to close the ‘Table Options’ window.

Define distance between spill points

The tool provides options for calculating the distances between the maximum spill points found at each cross-section:

1. Use distance along defined spill line
2. Use true distance between Max Z spill points
   Note:

   if the second option is chosen here, the distances calculated by Flood Modeller will likely be slightly different to the distance measured along the spill line, as illustrated in the following figure:
   

Name the IED file

The tool saves the spill line data in IED format. Specify a filename for the new IED file to be generated by clicking on ‘…’ to open the standard Windows Explorer browser window.

Save your data

The spill generator will calculate spill levels by analysing elevation data along mini cross sections drawn across the spill lines at regular intervals. Note: This process may take a few minutes if the grid is very large (as all points need to be checked to see if they lie along the specified mini cross sections). The process also always takes longer with non-binary grid data, i.e. ASCII text grid data.

The following options are given at the bottom of the spill unit tool to aid the user:

1. Plot – this opens a new window and plots the maximum elevation along each cross-section against distance for all spill lines. Click the box in the top right of the screen to deselect all spill lines, the box to the left of this checked in green to select all spill lines, or select/deselect spill lines individually via the checkboxes next to each node label.
   
   Along the bottom of the ‘Plot’ window are radial buttons to use the distance along the defined spill line or the true distance between the maximum elevations. The default will be the option selected earlier in the spill unit generation tool.
   A save option is provided on this screen to save the IED file in the location specified in step 6. If no file name was provided in the tool earlier, the standard Windows explorer browser window will open for you to provide a name and location for the IED file.
2. View – this allows you to view the generated data in text format. A save option is provided to save the IED file in the location specified in step 6. If no file name was provided in the tool earlier, the standard Windows explorer browser window will open for you to provide a name and location for the IED file.
   
3. Save – saves the IED file in the location specified in step 6. If no file name was provided in the tool earlier, the standard Windows explorer browser window will open for you to provide a name and location for the IED file.
4. Close – exits out of the spill unit generation tool. If you select this before saving your data to an IED file, the following window will pop up: