For RIV, DRN and GHB packages it should be possible to automatically assign them to the appropriate layers of the model.

[Manangka]

In GitLab by @HendrikKok on Nov 7, 2023, 10:41

This is especially relevant for MF6 models, since there are strict input checks.

Possible logic would be:

1. Assign to top active layer (for DRN and GHB for example)

2. Assign to one layer based on bottom- or stage level

3. Assign to all layers where stage or bottom > cell-bottom. Conductance should be distributed based on:

   a.	Intersection length
   b.	Transmissivity contributions
   C.      ...
   

Requirements:

• Create some place to store settings for each package.
• The user should be able to alter these settings, provide custom settings
• Create functions to find layer based on provided z value (could be bed level, could be elevation), option 2, and and a function which returns all active cells above a provided z value, option 3.
• For option 1, we can use the methods already added to imod.prepare.layer

Tasks

• Create utility functions to allocate RIV/DRN/GHB cells #949
• Create utility functions to distribute conductances #950
• Extend distribution of conductances options for drains #974
• Add missing documentation public API allocation utilities #975
• Create objects for planar grids which return Modflow 6 packages #951

[JoerivanEngelen]

Things to further refine:

• Which settings should be able to be altered?
• Where should these settings be stored?

[JoerivanEngelen]

See this report from Sweco describing different methods to allocate cells with depth and distribute conductances over depth in iMOD5. Nice summary of requirements for this story!

20240129 Conductanceverdeling iMOD5.docx

I translated the list of settings in iMOD5.6 briefly below. We could create a set of utility functions to support this, so that users can mix and match what they'd like.

Allocation RIV cells with depth:

• Laying inbetween river stage and bottom elevation (IDEFFLAYER=0)
• First active cell to bottom elevation (IDEFFLAYER=-1)
• First active cell to bottom elevation, cells above river stage can only drain (IDEFFLAYER=1)
• In cells where bottom elevation is located (IDEFFLAYER=2)

Distribution conductance with depth:

• "default" iMOD5 option whatever that means?
• equally over layers
• weighted by layer thicknesses
• weighted by protruded layer thicknesses
• weighted by layer transmissivity
• weighted by horizontal hydraulic conductivity