Topographic features

A Flood Modeller 2D simulation can include additional topographic features, e.g. representation of defence systems.
These are areas where you know the ground grid input data require modification, e.g. the addition of a building that blocks a flow path or where a bridge deck is masking an existing flow path (under the bridge arches). These modifications can be introduced to your model by the addition of point, polyline or polygon (ESRI) shapefiles that define the shape of the topographic feature and provide the revised ground elevation as an attribute. These files are called topographic feature shapefiles. They can be created in Flood Modeller (with the required attributes automatically defined) or any compatible GIS package.

The required attributes for a topographic shape file are:

• “height” – defines the revised level or modified level to be used for a polygon or point shape file.

• “height1” / “height2” - defines the revised level or modified level to be used for a polyline shape file. The two heights represent the values to be applied at start and end of each line. The 2D solver will then interpolate values between the start and end values along each line.

• “method” – this is an optional field that allows you to add or subtract the specified levels in the height fields to the underlying ground elevation. To activate this function enter “add” here. Then, for example, if you entered a height value of “-0.5” then underlying ground elevations will be lowered by 0.5m.

  If this field is missing or its value left blank (or set to “replace”) then the 2D solver will just replace underlying ground grid values with those specified in the topographic feature shape file.

  In some legacy models this field may not be present and there may be an attribute field entitled “isis2d” present instead. In this case the “isis2d” field will perform the same role as the “method” field and if left blank for a feature then the default option to replace underlying ground grid values will be invoked.

Note that the solver can accept polylineZ and polygonZ format shapefiles. It uses the following hierarchy: If a shapefile has an attribute table with a populated field entitled "height" or "height1", then these elevation data will always supersede the embedded Z values of the polylineZ/polygonZ.