Visited there today, and there was plenty of water in the channel, but it wasn't clear which way the water was actually flowing. If I had to guess looking at the map, I would say this is probably a drainage ditch with a very shallow gradient intended to provide additional drainage when the ground is very wet, and that it drains west to east into the pond in Duloch Park. The watercourse west of this marker is in roughly the location of the old right of way (Gypsie Lane) which emerges on the south side of the substation on Linburn Road. From memory, the land adjacent to the substation is slightly higher, and there's no culvert, so that would fit with the flow being west to east. Even the detailed OS mapping (available via pastmap.org.uk) doesn't show a direction on this watercourse.