Detect stopbank crest height

[rosepearson]

• Sample perpendicular to (smoothed?) specified stopbank
• Update the stopbank location
• Define stopbank crest height

DESCRIPTION OF PR:

• [ ] Make code change
• [ ] Update tests
  • [ ] Update / create new tests
  • [ ] Ensure these tests have the expected behavour
  • [ ] Test locally and ensure tests are passing
• [ ] Ensure tests passing on GH Actions
• [ ] Update documentation
  • [ ] Doc strings
  • [ ] Wiki
• [ ] Update package (version.py & pyproject.toml) version (if needed)