Overland flow paths are used to inform Level AI where low points can be in the roading network, if there is no overland flow paths in your model Level AI will assume the site must drain out via the roading network (where it snaps to the earthworks extent).
Add by clicking Drainage -> Overland Flow Path and then drawing out the path making sure to cross the road centreline and the earthworks extent boundary
Overland flow paths must cross the road centreline to activate. If they do not cross it but are snapped nearby, a Level AI validation warning will be generated when you run Level AI Prepare.
Cul-de-sacs
If you do not specify a overland flow path at a cul-de-sac it will drain out via the road connections, this may not be desirable. Adding an overland flow path allows the cul-de-sac to be a low point.
Drainage Paths
Where you allow a road to be low such that in a flood event water can spill out of the site add an overland flow path making sure it crosses the road centreline and earthworks extent. The point where the OLFP crosses the earthworks extent is important as this is the elevation Level AI considers when setting elevation of the road where OLFP crosses it.
Connecting Roads
Additionally Overland Flow paths can be used to 'connect' 2x roads, informing Level AI that water can flow between the 2 roads in a flood event.
Near Ponds
If you have an overland flow path near a pond you can choose to run it through the pond in which case the road will always be higher than the pond lip level. It still needs to run out of the site to activate.
Alternatively you can run the OLFP directly out the site avoiding the pond, this tells level ai the road needs to be higher than the ground at existing ground by the overland flow path.
Step-by-Step Guide
Below is a guide showing process to add overland flow paths to your model.
