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  "assumptions": [
    "Skogerboe cutthroat free flow: Q_cfs = C Ha_ft^n; C=3.50 W_ft^{1.025} (L_f/3 ft)^{0.020}; n=1.56 (L_f/3 ft)^{0.026}; SI W, L_f, Ha, Q; C and n are reported, not inputs",
    "No diverging section; L_f is independent flume length, not weir crest L; W < L_f; L_f∈[0.4572 m, 2.7432 m]; W∈[0.0508 m, 1.8288 m]; Ha∈[0.03048 m, 1.2192 m]",
    "Not Parshall 4 W_ft Ha^{1.522 W^{0.026}}, not thin-plate weir, not broad-crested (2/3)^{3/2} √g, not Manning n, not Q=Av, not orifice, not submerged Hb"
  ],
  "limitations": [
    "Skogerboe cutthroat free flow: Q_cfs = C Ha_ft^n; C=3.50 W_ft^{1.025} (L_f/3 ft)^{0.020}; n=1.56 (L_f/3 ft)^{0.026}; SI W, L_f, Ha, Q; C and n are reported, not inputs",
    "No diverging section; L_f is independent flume length, not weir crest L; W < L_f; L_f∈[0.4572 m, 2.7432 m]; W∈[0.0508 m, 1.8288 m]; Ha∈[0.03048 m, 1.2192 m]",
    "Not Parshall 4 W_ft Ha^{1.522 W^{0.026}}, not thin-plate weir, not broad-crested (2/3)^{3/2} √g, not Manning n, not Q=Av, not orifice, not submerged Hb"
  ],
  "boundary_conditions": [
    "missing W, L_f, Ha, or Q when required → MISSING_REQUIRED_INPUT",
    "Ha and Q together, weir H/L/b, Manning n/R/S, orifice A/d/D/Δp, Q=Av v, yc/q/Fr/g, Cd, Hb, W_ft, kind=parshall → MIXED_INPUT_ENCODING",
    "L_f outside [0.4572, 2.7432] m, W outside [0.0508, 1.8288] m, W ≥ L_f, or Ha outside [0.03048, 1.2192] m → VALUE_OUT_OF_RANGE",
    "mode=rectangular|thin-plate|broad-crested|parshall or unknown mode → MIXED_INPUT_ENCODING or INVALID_MODE"
  ],
  "sources": [
    {
      "title": "Skogerboe, G.V.; Hyatt, M.L.; England, J.D.; Johnson, J.R. — Design and Calibration of Submerged Open Channel Flow Measurement Structures, Part 3: Cutthroat Flumes",
      "section": "3-ft family free-flow rating",
      "supports": "C=3.50 W_ft^{1.025} and n=1.56 at L_f=3 ft; L-scaled n and C; not a Parshall 4 W rating",
      "kind": "reference"
    },
    {
      "title": "ISO 80000-4 — Mechanics",
      "section": "Volume flow rate",
      "url": "https://www.iso.org/standard/31895.html",
      "supports": "Q is volume flow; W, L_f, and Ha are lengths",
      "kind": "standard"
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