Editing the terrain – Subsurface edits

Workspaces let you change your terrain model and observe the effects on the analyses. This section discusses the subsuface terrain editing tools that, although not directly changing the terrain, allows you to change how water flows in your workspace.
For an overview of the workspace editing process please consult the introduction page.

Subsurface structure

Creates a subsurface structure between the two end points of the path. The edit does not change any elevation on the terrain, but it allows water to be transported between the end points without affecting the terrain between them. The subsurface structure will transport an unlimited amount of water, but it does not store any water itself – it has zero volume.

Usage example: Model culverts and underpasses without obstructing flow over the top of the structure.

Subsurface basin and sewage drains

Creates a sink point on the surface connected to a subsurface basin with a specified volume. This volume can either be typed in manually or set to an event-specific runoff volume from the watershed of the sink point. This runoff volume is determined by first clicking query runoff next to the volume input field and then, selecting the sink point position on the map. The event determining the runoff volume can be varied by dragging the rain slider which appears when clicking query runoff.

Usage example: Model the effect of a subsurface basin or a sewage drain with a guaranteed service level (e.g. a sewage drain dimensioned to handle the runoff volume for a 15mm rain event).