renamed hydrology constants

[vgro]

This PR renames a few hydrology constants that were unclear.

Fixes #783

Type of change

• New feature (non-breaking change which adds functionality)
• Optimization (back-end change that speeds up the code)
• Bug fix (non-breaking change which fixes an issue)

Key checklist

• Make sure you've run the pre-commit checks: $ pre-commit run -a
• All tests pass: $ poetry run pytest

Further checks

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works
• Relevant documentation reviewed and updated

[jacobcook1995]

LGTM! (just had one small question)

[jacobcook1995]

What does Campbell mean here, is it from a specific model?

[vgro]

I added the reference to the constants; the reference is also in the function docstring.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.51%. Comparing base (93e79f1) to head (4877159).
⚠️ Report is 2415 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #784   +/-   ##
========================================
  Coverage    94.51%   94.51%           
========================================
  Files           74       74           
  Lines         5013     5013           
========================================
  Hits          4738     4738           
  Misses         275      275           

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