Flow verification module: automated reversed-section detection

[jameshgrn]

Summary

Built an automated flow verification system that detects and validates reversed flow directions at the section level (junction-to-junction segments). The module is functional but yields are low — parking for now to refocus on higher-impact POM fixes.

What exists

• src/sword_v17c_pipeline/flow_verification.py — full module with:
  • Multi-signal scoring: DEM WSE slope, SWOT WSE slope (Theil-Sen at node level), facc monotonicity, junction slope validation
  • Confidence tiers: HIGH / MEDIUM / LOW / SKIP
  • Quality filters: ghost junctions (type=5/6), all-lake sections, single-reach sections, all-ghost sections
  • Pre-flip verification: DAG check, connectivity preservation, outlet reachability, facc improvement
  • Batch DuckDB writes with provenance + rollback support
• scripts/topology/fix_reversed_sections.py — CLI with --dry-run, --apply, --rollback
• tests/sword_duckdb/test_flow_verification.py — 30 passing tests
• Figures in figures/flow_verification_NA/ and figures/flow_verification_all/

Results (dry-run, all regions)

Region	Approved	Rejected	Low	Skip
NA	3	15	71	731
SA	2	8	204	171
EU	4	2	62	127
AF	1	3	47	108
AS	9	13	331	369
OC	1	1	18	160
Total	20	42	733	1,666

Why parking

1. Low yield: 20 approved flips out of 2,032 invalid sections (1%)
2. Small global impact: fixes 46 of 4,814 WSE inversions (~1%), essentially zero facc improvement
3. DEM signal dominance: MERIT Hydro WSE always has data, SWOT is sparse. DEM controls the vote but is lower quality than SWOT on flat rivers
4. Diminishing returns: Most remaining invalid sections are ambiguous — flat rivers where noise dominates signal

To pick back up

1. Drop DEM as a signal — SWOT-only scoring would be higher confidence per flip but even fewer approvals
2. Tighten slopes_plus_supporting — AS section 18081 was approved despite SWOT actively contradicting DEM (DEM=+0.39, SWOT=-0.40). Require no signal actively contradicts.
3. Or ship the ~17 clean ones — drop 3 sketchy sections (AS 18081 etc.), apply the rest, move on

Related

• Investigate 4,816 WSE inversions downstream (A030) #195 (WSE inversions — this module addresses ~1% of those)
• Branch: topology-fix