Nodes of different colours represent the following:
Solid arrows point from a submodule to the (sub)module which it is
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modules which it uses.
Where possible, edges connecting nodes are
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~ ~ ~ PURPOSE ~ ~ ~
this subroutine writes annual gwflow output in SWAT+ long format:
one row per active cell with average head, wtdepth, and average
daily flow rates; basin-level water/heat/solute balance; HRU pumping