How to create link-lines manually

This section explains how to manually draw link-lines to integrate a 1D river network and 2D components. An easier method is to instead Use the link-line generator which automates much of this process.

1. Open Flood Modeller and use the Add GIS Data button tool (Home tab of main toolbar) to load the appropriate datasets to the map view that will help define the location of your link lines. These data may be one or more of the following datasets (from your 2D model):
   • A 1D model network or a point shape file representing your model nodes (e.g. an imported gxy file from a 1D model). Note that this assumes your 1D model has geo-referencing information available. If this is not available then please first review the Flood Modeller user guide section on how to geo-reference a 1D model.
     Useful tip:

     If your 1D network sections already define some part of the floodplain, i.e. they extend beyond the bank edges, then you may want to exclude these out of bank areas from the 1D model and let the 2D model simulation flooding here. You can edit cross sections, removing the out of bank points, to achieve this. Alternatively you can add deactivation markers to the sections at the bank edges (the Tiikbox includes a tool to automatically convert all bank markers in a model to deactivation markers).

     When you drag a 1D network on the map, Flood Modeller will check it for deactivation markers. If any are present you will be asked if you only want to show the active (in-bank) parts of each cross section in the map view. Selecting this option enables you to draw link-lines and/or 2D active areas that trace along the bank edges of your 1D network, i.e. the true boundary between the 1D and 2D elements of your model.

   • An active area polygon shape file – along which you want your link lines to trace (along the edges). Note you can define a different polygon to trace along if the link lines are not to be located at the edge of a domain.
   • Ground elevation dataset, i.e. DTM. This is an optional dataset as the generation of link lines does not require ground elevation data. However, you can choose to populate your link line height attributes with levels taken from an underlying ground grid, e.g. if these data include flood defence heights that are not present in the ground grid input for your 2D model.
2. There are two options to manually create a new 2D link line file:
   • On the 2D Build tab of the main toolbar select Level Link, Flow Link or Weir Link from the 1D-2D Link Lines section. Specify a filename and location to be used for your new link line shape file when prompted.
     
   • Select New > Shape file from the Home tab. A new window is displayed in which you can select to create a new ‘1D 2D Model link line’ shape file. After specifying your new file, name and location click the OK button to continue.
     
3. Flood Modeller will add your new file to the Layers Panel and go into layer edit mode, i.e. the layer editor toolbar will be displayed in the main toolbar and editing tools will be enabled. You have the option to start drawing link lines in your map view (click the Draw button to start).
   Alternatively if you have 1D cross sections or a 2D active area polygon shapefile loaded in you map view you can trace along the edges of these to create link lines exactly on the boundary between your 1D and 2D model areas. To activate snapping before you start drawing:
   • Click the Snapping button in the toolbar (Properties section on right side)
   • The snapping control window will be displayed listing all compatible layers currently in the map view. This enables you to select a layer (or multiple layers) to snap to. Options are:
     • Snap drawn lines onto the edge of your active area shape file – select snap to “Any Point”
     • Snap drawn lines onto ends of 1D cross sections – select snap to “Start Point”, “End Point” or “Both End Points”
   • After defining your snapping apply the settings by closing the window (click the “X” in the upper right corner of the snapping control window).
   • When you start drawing now the draw cursor will jump to the nearest point defined by your snapping settings. You should see a dotted line box appear around the point that the draw cursor will try to jump to.
     
4. It may be helpful before starting to draw your link lines to activate labels for your 1D nodes:
   • For a 1D network file click the labels tick box on the Home tab of the main toolbar.
   • For a point shape file this is done in the layer properties window. On the labels tab select the attribute field that holds the 1D node names and click the display attribute tick box.
5. Use the pan and zoom tools to position the map view where you wish to draw your link line. Having selected your link line in the Layers panel, click on the Line button in the Layer editor toolbar to activate the drawing tool on your map (the mouse pointer will change to a pencil icon). Proceed to draw your link line using one of the following methods:
   
   Trace along the edge of your active area polygon
   • If you are using snapping then move the cursor close to the active area layer - a dotted line box should be visible around the closest point to your cursor. Click to add a point
   • Move along the active area edge to the next point. When you get close you should see the box appear around the next point. Click the mouse again to add a point.
   • Repeating this process, subsequent clicks will add further points to your new link line.
   • A double-click will end the current line (should be close to the next 1D node).
   • You will remain in drawing mode so a subsequent click will start a new line.
   • Continue adding further link lines (between adjacent 1D node points)
   • To stop drawing click the Select button in the Editor toolbar (the pencil icon of the mouse pointer will change back to a standard pointer).
     
     Join up the end points of your 1D cross sections
   • If you are using snapping then move the cursor close to the layer representing your 1D cross sections - a dotted line box should be visible around the closest point to your cursor. Click to add a point.
   • Add further points as you draw a line to the next section. This line will define the boundary between 1D and 2D models and so will also define the edge of your active area (with this method the link line is drawn first and you can then use snapping to trace the active area along the link lines).
   • Move the cursor close to the next cross section end point. When you get close you should see the box appear around the next point. Double-click the mouse to add a point here and at the same time end drawing the current line.
   • You will remain in drawing mode so now draw the next link line. Start at the end point of the last line, draw the link line points along the edge of your 1D model and finish at the next cross section.
   • Continue adding further link lines (between adjacent 1D sections)
   • To stop drawing click the Select button in the Editor toolbar (the pencil icon of the mouse pointer will change back to a standard pointer).
     
     Free drawing of link lines
   • If you are not using snapping then move the cursor to where you want to start your first link line. Click to add a point (should be close to a 1D node).
   • Subsequent clicks will add further points to your new link line. Remember that link lines must lie within (or on) the boundary of your 2D active area.
   • A double-click will end the current line (should be close to a 1D node).
   • You will remain in drawing mode so a subsequent click will start a new line.
   • Continue adding further link lines (between adjacent 1D node points)
   • To stop drawing click the Select button in the Editor toolbar (the pencil icon of the mouse pointer will change back to a standard pointer).
   • A useful tip is to remember that you can still use the pan and zoom controls while drawing to enable you to move to a different area of the map
     
6. After drawing your lines it is probably a good idea to save your link line shapefile – click the Save button in the Editor toolbar.
7. The attribute table of your link line shape file will be updated with a new row every time a new line feature is drawn. The attribute fields will not be populated with any values, so these then need to be added manually. To change an attribute then, while in edit mode, click on a row in the attribute table and type in attribute values for the selected feature. With the manual drawing of link lines all required attributes must be typed in manually. Repeat this editing procedure until your attribute table is fully populated, as shown by the example below:
   
8. Once all links have been completed (or at any time) your new link line shape file can be saved by clicking the Save button in the File menu (of the Layer Editor toolbar). Alternatively if you right click on the file name in the Layers panel you can select the Stop Edit option from the displayed menu. This will give you an option to save your file as you exit the edit mode.