Paid tier only. Calling this without an authenticated CivilQuants account returns TIER_INSUFFICIENT — sign up at https://civilquants.com/pricing or use the free-tier alternative compute_manhole. Linear primary measurement of an open earthwork drainage channel — trapezoidal cross-section, four lining variants (unlined / geotextile / granular / concrete). Routes via CESMM4 Class E.4 (excavation for cuttings), NRM2 Group 34.10 (site works: open drains and ditches), MMHW Series 500.4 (SHW Cl. 514 Earthwork ditches and drains), SMM7 R13.4 (Land Drainage — ditches). Eight variant presets cover all four lining types x two characteristic size scenarios each. Unit: M. Second member of the drainage_ancillaries L2 leaf (opened at S32 with connection_to_existing). 20th use of the classed-then-legacy attribute discrimination pattern via the lining_type discriminator. The four standards genuinely diverge on which work-section heading owns ditches (Class E vs Group 34 vs Series 500 vs R13) — the platform renders all four honestly from one source WorkItem. Example params: run_length_m=100 m (1–1000), top_width_mm=1700 mm (200–10000), bottom_width_mm=500 mm (100–5000). Example call: {"params": {"run_length_m": 100, "top_width_mm": 1700, "bottom_width_mm": 500}, "standard": "MMHW"}. Omitted parameters use sensible engineering defaults. Pass deliverables=["xlsx","dxf","pdf"] (any subset) to also receive one-shot download URLs in the same call: Excel BoQ (both tiers, watermarked free) plus the dimensioned DXF (CAD) and PDF drawing sheets (paid tier).