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Parity & tolerances (engineering verification)

Even for a legacy desktop tool, documenting expected numeric behavior and acceptable tolerances improves reviewability and reduces regression risk.

Initial tolerance seeds (legacy parity spec)

  • Peak discharge: \(\le \max(0.1\ \text{cumecs}, 3\%)\)
  • H/D, depth values: \(\le 0.03\)
  • Velocity: \(\le 0.05\ m/s\)
  • BOQ quantities: \(\le 2\%\)
  • GIS area/length: \(\le 2\%\)

What “parity” means in practice

  • Correct method selection (Rational vs SCS by threshold).
  • Correct IDF segment selection and intensity retrieval.
  • Stable culvert control selection and governing headwater ratio.
  • Stable channel regime classification for identical inputs.
  • Trend consistency for gully spacing and bypass progression.
  • BOQ category totals within acceptable engineering tolerance.