Interesting question, after a quick perusal, I think given the Riverview siding is on the only cultivatable patch of rivers edge, that it is the oddity. That ditch may precede the siding date, thus requiring the seperation or the topography led to the ditch being dug where it is regardless of the siding, who knows? It is certainly different from the normal passing sidings and mainline locations I had a quick squiz at.
NZR was fond of lowering the passing tracks making getting ones bag and self up on to the Loco at changeover a heck of a stretch.
C&S doesn't appear to have favoured raising the main, but it may just be a case by case and time period scenario to consider. There is certainly no shortage of pictures on which to base your choice but these pictures are scattered throughout all the usual C&S books, and my illustrations are not the areas that you want to model either.
Cliff.
http://cdm16079.contentdm.oclc.org/cdm/fullbrowser/collection/p15330coll22/id/4516/rv/singleitem/rec/1South Platte.
http://cdm16079.contentdm.oclc.org/cdm/fullbrowser/collection/p15330coll22/id/12914/rv/singleitem/rec/1Webster seemed to be elevated slightly as did Crossons.
http://cdm16079.contentdm.oclc.org/cdm/fullbrowser/collection/p15330coll22/id/42523/rv/singleitem/rec/2
UpSideDownC
in New Zealand