Remove validation error for regional rivers

[James Bruten (james-bruten-mo)]

PR Summary

Code Reviewer: Sam Clarke-Green (@t00sa)

The mule validators raise an error if trying to run with regional rivers. However this is no longer valid (see this discussion). This removes the validation error for these scenarios.

Code Quality Checklist

(Some checks are automatically carried out via the CI pipeline)

• I have performed a self-review of my own code
• My code follows the project's style guidelines
• Comments have been included that aid undertanding and enhance the
  readability of the code
• My changes generate no new warnings

Testing

• I have tested this change locally, using the rose-stem suite
• If any tests fail (rose-stem or CI) the reason is understood and
  acceptable (eg. kgo changes)
• I have added tests to cover new functionality as appropriate (eg. system
  tests, unit tests, etc.)

trac.log

Test Suite Results - um - um_for_mule_rivers/run1

Suite Information

Item	Value
Suite Name	um_for_mule_rivers/run1
Suite User	james.bruten
Workflow Start	2026-07-16T08:26:02
Groups Run	mule

Dependency	Reference	Main Like
casim	MetOffice/casim@2026.07.1	True
jules	MetOffice/jules@2026.07.1	True
moci	MetOffice/moci@2026.07.1	True
mule	james-bruten-mo/mule@rivers_validation	False
shumlib	MetOffice/shumlib@2026.07.1	True
socrates	MetOffice/socrates@2026.07.1	True
SimSys_Scripts	MetOffice/SimSys_Scripts@2026.07.1	True
ukca	MetOffice/ukca@2026.07.1	True
um	MetOffice/um@9c139d0	True
um_aux	MetOffice/um_aux@2026.07.1	True
um_meta	MetOffice/um_meta@2026.07.1	True

Approvals

Code Owners

• No UM Code Owners Required

Config Owners

No UM Config Owners Required

Task Information

✅ succeeded tasks - 43

Security Considerations

• This change does not introduce security vulnerabilities
• I have reviewed the code for potential security issues
• Sensitive data is properly handled (if applicable)
• Authentication and authorisation are properly implemented (if applicable)

Performance Impact

• Performance of the code has been considered and, if applicable, suitable
  performance measurements have been conducted

AI Assistance and Attribution

• Some of the content of this change has been produced with the assistance
  of Generative AI tool name (e.g., Met Office Github Copilot Enterprise,
  Github Copilot Personal, ChatGPT GPT-4, etc) and I have followed the
  Simulation Systems AI policy
  (including attribution labels)

Documentation

• Where appropriate I have updated documentation related to this change and
  confirmed that it builds correctly

Code Review

• All dependencies have been resolved
• Related Issues have been properly linked and addressed
• CLA compliance has been confirmed
• Code quality standards have been met
• Tests are adequate and have passed
• Documentation is complete and accurate
• Security considerations have been addressed
• Performance impact is acceptable

[Sam Clarke-Green (t00sa)]

Looks sensible but we might as well fix a spelling mistake in the comment while we're at it...

[Sam Clarke-Green (t00sa)]

Approved!

[Sam Clarke-Green (t00sa)]

Re-approving after merge