Runs and structures

How a run connects two structures, which end owns what, and why branches do not double-count.

A run is one pipe between two structures. It has a direction, and the direction is the whole model:

• From (FID) - the upstream end, the first point, carrying the upstream invert.
• To (ID) - the downstream end, the last point, carrying the downstream invert.

Water flows from the From end to the To end, from the higher invert to the lower, and the slope falls out of the two:

Slope = (downstream invert − upstream invert) ÷ length

Which run owns a structure

Each structure is owned by exactly one run - the run whose To end it is. A structure comes into existence as some run's downstream end.

Sharing happens on the From side. Several runs can pull from the same upstream structure - a branch where two runs both start at structure 5 is completely normal, and it does not double-count. The structure is still owned once, by the run that ends at it.

This is worth internalising before you look at a quantity and worry. A branching network has more From references than structures, by design. Nothing is counted twice.

Placing a structure on its own

A structure with no pipe yet is a run whose From and To are the same: a single point, no length. That is the normal way to place a structure ahead of the runs that will connect to it - drop the manholes first, then draw runs that snap to them as their From end and measure away to their To.

The panel columns

The panel lists runs two ways.

By structure:

By pipe: