Rational Method Peak Runoff Calculator implementation

Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

Record owner

Guth Instruments

Lifecycle

verified-clean

Evidence ID

t7-114

Effect

Computation or source lookup only

Input and validation requirements

The specification has no unit-conversion or sign-convention definition, does not explicitly enforce the strict less-than-200-acre scope boundary, and permits extreme inputs that overflow ordinary arithmetic. It also has no true mathematical formula branch; only an applicability switch can be tested.

Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

{
  "inputs": {
    "C": 0.9,
    "surface_type": "impervious roof",
    "i": 100,
    "i_units": "mm/h",
    "A": 2,
    "A_units": "ha",
    "output_units": "m^3/s"
  },
  "expected_outputs": {
    "Q": 0.5,
    "Q_units": "m^3/s"
  },
  "reference_data": {
    "runoff_coefficient": {
      "surface_type": "impervious roof",
      "C": 0.9,
      "source_convention": "widely tabulated standard value (ASCE/municipal Rational Method tables)"
    },
    "rainfall_intensity": {
      "duration": "local IDF duration equal to time of concentration",
      "i_mm_per_h": 100,
      "source_convention": "user-supplied local IDF data; geographic source and return period must be specified"
    },
    "si_conversion_factor": {
      "value": 360,
      "meaning": "Q(m^3/s)=C*i(mm/h)*A(ha)/360",
      "source_convention": "SI dimensional conversion from hectare and millimetre per hour"
    }
  },
  "working": "Q = C*i*A/360 = 0.90*100*2/360 = 180/360 = 0.500 m^3/s. The C=0.90 value is used exactly as the tabulated impervious-roof entry."
}

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche7/tranche7-results.json