Investigate if forcing IHC=2 leads to any performance issues

We want to add support for IHC mode 2

Notes:

• According to the Modflow readthedocs:
  ihc is an integer flag indicating the direction between node n and all of its m connections. If IHC = 0 then the connection is vertical. If IHC = 1 then the connection is horizontal. If IHC = 2 then the connection is horizontal for a vertically staggered grid.

• We don't expect many changes for supporting IHC=2 mode. The cl1,cl2 and hwva values should be computed the same way as for IHC1. CDist does differ and needs to be accounted for. In most cases the vertical component
  of the distance of CDist is negligible

• We won't implement IHC=0. We only support horizontal partitioning

Questions:

• Would forcing IHC=2 lead to any performance issues

Notes:

• Ask Martijn about any theoretical consequences
• Do stress test, preferably with converted LHM case (Ask Teun or Huite for this data)

Start by reviewing the Modflow definition of IHC=2 and consult Martijn about its theoretical consequences. Obtain a converted LHM case from Teun or Huite, then run stress tests comparing IHC=1 and forced IHC=2 behavior and performance. Done means documenting whether performance or correctness is affected and identifying the required implementation scope.