We just have accepted a paper related to the topological ordering we use inside our model JGrass-NewAGE. This ordering derives is a generalisation of the Pfafstetter algorithm.
Once understood, it can be observed that this Pfafstetter ordering can be used to drive, for instance parallel execution of operations. But this is another story. We actually use to orderly process the basin partition in JGrass-NewAGE modules. The paper, entitled "Digital watershed partition within the NewAGE-Jgrass system" by Formetta et al. can be downloaded from here.