How to create a 2D model boundary

Required type of file: Polyline shapefile

Overview

Flood Modeller 2D models require boundary condition data to provide inputs to drive a simulation. Boundary conditions are defined as polylines (or points) with attributes that reference time series data or with links to an associated 1D hydrodynamic model.

A standard boundary is defined by any polyline shapefile (with appropriate attributes) drawn within an active area polygon.

Flood Modeller also provides the functionality to define a boundary line that traces along the edge of an active area polygon. This type of boundary can be used when linking to an associated 1D model.

Creating a Standard Boundary Polyline

The following procedure enables the creation of a standard boundary polyline:

1. Select the “Boundary Line” button from the 2D Build tab of the main toolbar.

2. Alternatively, you can create a new shapefile from the Home tab by clicking on New > Shapefile and selecting “2D Boundary Line (custom polyline)”.

3. You will be prompted to specify a filename and location for your new shapefile.

4. The Layer Editor Toolbar will then be activated. The Snapping Tool, which lists the currently loaded files that can be snapped to when drawing your new boundary line, can be opened from here. You can select one or more layers to snap to if required by placing a tick next to the appropriate filename, e.g. if you want to trace along a particular edge of an existing shape (see below for further details).

5. To start drawing a new boundary, click on the “Line” button.

6. You can start drawing by clicking on the Mapview at the appropriate start location for the boundary line. Each left click then adds a new point to the line. Right clicking on the viewport presents a menu with options to remove the last point added or to finish drawing the line. A double left click also ends drawing of the line.

7. A useful feature is that the zoom and pan tools can still be used while a line is actively been drawn. Zoom is always available by using the mouse central scroll wheel (if available). Alternatively, if you click on the plus and minus buttons in the top left corner of the map, you can zoom in or out of the map view as well as use the pan tool. The drawing will be paused while you move the map.

8. If a boundary is to be applied to just a single cell within the model extent, then this must still be defined as a polyline. The line must be short enough to be confined to the relevant cell. Alternatively you can choose to create a standard point shapefile (using the New > Shapefile button on the main toolbar) and then manually define any attributes you want assign to the file. Note that you can assign a single time series input to a shapefile with no 2D specific attributes. Alternatively you can assign a multiple time series file (csv or ied) to a boundary shapefile with the attribute field ‘node’ used to cross reference between shapefile features and time series headers.

9. When all required boundary lines are defined, then save the shapefile and exit from the shapefile editor.

Creating a Boundary along the Edge of an Active Area Polygon

The following describes how to create a boundary line that traces precisely along the edge of an active area polygon shapefile:

1. Use the “Add GIS Data” button on the main toolbar to load the Active Area polygon you wish to trace over

2. Follow the above instructions to create a new boundary line shapefile.

3. The shapefile editing toolbar will then be activated. The snapping menu can be activated from the Layer Editor tab.

4. To trace along the edge of your 2D active area, select only the Active Area shapefile in the list of available files to snap to (by clicking on tick box).

5. Set the snapping criteria to 'Any point' to allow any part of the active area to be traced. Other snapping options are start point only, end point only and both end points (these are used in the generation of other model specific shapefiles).

6. Now start drawing the new boundary line by clicking on the “Line” button from the Layer Editor Tab.

7. As the curser is moved close to the active area it will 'jump' to the closest active area point enabling a line to be constructed that traces the underlying active area polygon.

8. It is usually easier to trace along an active area when zoomed in close to the line. In this case you can use the zoom and pan tools while in drawing mode to move to different parts of your GIS data as you traverse across the map view.

9. When all required boundary lines are defined, save the shapefile and exit from the shapefile editor.