Generating Overland Flow Paths - From Background Layer

Links and nodes of system type "Overland" representing the Overland Flow Path can be automatically generated based on a starting selection of existing nodes and lines in a GIS background layer (road centre lines).

The overland flow path generation process is carried out as follows:

• The GIS layer data is filtered by attribute as defined in the Generate Overland Flow Paths Dialog.
• GIS layer lines are processed resulting in a set of polylines for use in flow path generation:
• Lines that form crossroads but do not quite meet are extended to meet
• Polygons (that fit within a bounding square of 20 m width) are imploded into a line
• Each selected node is attached to a polyline within snapping distance of the node via an extra line segment. The order of preference for attaching nodes to lines is:
• Attach node to end of the closest free (i.e. not junction point) layer line endpoint
• Attach node to closest junction point
• Attach node to closest line. The chosen line is split and the node is attached to both parts of the line

Sealed Manholes, Outfalls or nodes that are already connected to a downstream Overland link will not be attached to a polyline.

• Any lines not attached to a node are discarded. The remaining lines are used to create corresponding overland links. Overland storage nodes are created at points where overland links cross.

The new overland links and nodes and existing nodes are connected up. The flow path will be terminated if:

• The flow path reaches the extents of a background layer line
• The flow path reaches the extents of a bounding polygon (if bounding polygon specified)

For flow paths that do not snap to the network, there is the option to create an overland link connected to an outfall node at the point at which the flow path terminates.

To generate Overland Flow Paths using background layer lines:

1. Select the nodes on the GeoPlan from which Overland Flow Paths are to be traced.
2. Select Generate 1D overland flow paths | From background layer lines from the Model menu. This displays the Generate Overland Flow Paths Dialog.
3. Set parameters on the Generate Overland Flow Paths Dialog:
• Bounding Polygon (optional): Only selected nodes within the polygon will be traced from. The trace will be terminated if it reaches the extents of the bounding polygon.
• Snapping Distance: The distance to a link / node or background layer line that overland flow path must be within, before snapping will occur.
• Layer containing background lines: Dropdown list of layers currently loaded on the GeoPlan. Click the Change Layers button to display the GIS Layer Control Dialog. Check the Remove layer after import box if the layer is not further required.
• Filter on line attribute: Only lines with the specified attribute values will be used to create overland links.
• Flow paths that fail to rejoin network: An overland link and outfall node will be created for paths that fail to rejoin the network only if the Create a link and outfall option is checked.
• System Types: Snapping of the overland flow path to the existing network will be allowed only to selected system types.
• Digitisation Defaults: Change digitisation defaults for use when creating new overland links and nodes.
4. Click OK

Overland links and nodes will be generated according to the settings on the Generate Overland Flow Paths Dialog. Nodes and links created are added to the current selection as the operation progresses.

Note that new nodes created by snapping to overland links are not derived from digitisation defaults. These nodes will be created as overland storage nodes with dimensions derived from the links that they join.

An HTML log will be displayed containing details of the flow path definitions.