Culvert/Pipe Sizing 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

t6-124

Effect

Computation or source lookup only

Input and validation requirements

Zero slope and zero Manning roughness produce undefined or nonphysical results unless explicitly rejected. The percent-slope convention can also produce a materially wrong diameter if the input is interpreted as S=1 instead of S=0.01.

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": {
    "design_Q_m3_per_s": 3.11685,
    "manning_n": 0.01,
    "slope": 0.01,
    "max_fill_ratio": 1,
    "assumed_design_fill_ratio": 1,
    "solver": "Newton-Raphson",
    "initial_diameter_m": 0.8,
    "tolerance_m": 0.000001
  },
  "expected_outputs": {
    "required_diameter_m": 1,
    "hydraulic_regime": "full circular pipe",
    "geometry_coefficient_C": 0.311685,
    "capacity_check_m3_per_s": 3.11685
  },
  "working": "For full flow, A=pi D^2/4 and R_h=D/4. Therefore Q=(1/n)(pi/4)(1/4)^(2/3)S^(1/2)D^(8/3)=K D^(8/3), with K=(1/0.01)(0.311685)(sqrt(0.01))=3.11685. Thus D=(Q/K)^(3/8)=(3.11685/3.11685)^(3/8)=1.00000 m. Newton solve on F(D)=D^(8/3)-1: D_(k+1)=D_k-(D_k^(8/3)-1)/[(8/3)D_k^(5/3)]. Starting D0=0.800000 m: D1=0.800000-(0.800000^(8/3)-1)/[(8/3)(0.800000^(5/3))]=1.04394 m. D2=1.04394-(1.04394^(8/3)-1)/[(8/3)(1.04394^(5/3))]=1.00153 m. D3=1.00000 m; convergence is below 0.000001 m. Check at D=1: Q=(1/0.01)(pi/4)(0.25)^(2/3)(0.01)^0.5=100(0.311685)(0.1)=3.11685 m^3/s."
}

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-tranche6/tranche6-results.json