Creeping the rope is basically lowering a person but VEEEERY slowly.
Creeping the rope involves rigging an unlocked releasable system at the anchor (unlocked figure 8 contingency block, munter or other) and slowly releasing the rope (e.g. 1/2 inch ever 3 seconds) so the abrasion point is never the same on the rope.
It is recommended to set the rope coming out of the block through the personal descender of the person manning the station to avoid the risk of getting distracted and letting go of the rope. It also serves as a backup anchor.
The last person down should lock the figure 8 contingency prior to going down, or use another system to faciliate the pull (e.g. biner block) and should be the most experienced rappeler in the group. LPAR should rappel carefully and smoothly to minimize the risk of abrasion or coreshots.
Creeping the rope is the most effective way to protect the rope in swift water.
Having the rope go through the personal descender of the person manning the station has additional advantages. The person manning the station should be familiar on how to operate his descender to provide faster/slower release and also on how to lock it, so his hands can be quickly freed for some other task without risking dropping the rappeler.
Creeping the rope is not possible for LAMAR, but it can be solved by means of a Bottom anchor or Traveling double rope.
Creeping the rope may accumulate rope at the end of the rappel, which can be dangerous in swift water pools. In this circumstances rope should be pulled back up after every rappeler disconnects and start the creeping process all over again.
The person manning the station will also be acting as a backup anchor, so make sure he/she is always secured away from the edge or clipped in to an alternate anchor point. Otherwise if the main anchor fails, both will go with it. If there are no alternate anchors this risk might be unavoidable.