Nodes of different colours represent the following:
Solid arrows point from a submodule to the (sub)module which it is
descended from. Dashed arrows point from a module or program unit to
modules which it uses.
Where possible, edges connecting nodes are
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~ ~ ~ PURPOSE ~ ~ ~
this subroutine calculates the water exchange volume between irrigation canals and connected grid cells
for canals that divert water from a source outside of the model domain.