Open-Channel Flow — Manning's Equation

Inspectable records

Ledger state

The current ledger marks this instrument verified clean within the source-bound verification corpus.

Area

Mechanical, Civil & Structural Engineering — Statics/Dynamics, Strength of Materials, Machine Design, Civil, HVAC, Vibration

Tranche

tranche-6

Evidence ID

t6-120

Ledger rows

1

No ledger note is attached.

Review findings

Forward Manning calculations pass the standard formula checks under the stated unit assumptions. Verdict is NEEDS_REVIEW because the specification is ambiguous about the exact US coefficient and pipe regime, and it claims inverse normal-depth output without defining the iterative algorithm or convergence tolerance.

Formula and scope findings

• The forward formulas are standard: V=(1/n)R^(2/3)S^(1/2), Q=VA, and R=A/P.
• The inverse normal-depth capability is underspecified: the target quantity (usually Q), channel geometry function, iterative method, initial guess/bracketing, stopping criterion, and convergence tolerance are not defined.
• The wording 'pipes' is ambiguous: Manning's open-channel equation applies to a partially full pipe using the wetted area and wetted perimeter; a full pressurized pipe requires a different hydraulic model.
• The US coefficient 1.49 is an accepted rounded form, but the specification should state whether US customary calculations use 1.49 or the more precise 1.486.

Unit assumptions

• SI case: lengths in m, A in m^2, P and R in m, n dimensionless, S dimensionless slope expressed as m/m, V in m/s, and Q in m^3/s; the coefficient is 1.
• US customary case: lengths in ft, A in ft^2, P and R in ft, n dimensionless, S dimensionless ft/ft, V in ft/s, and Q in ft^3/s; the coefficient 1.49 is used.
• A slope entered as a percentage must be divided by 100 before using S; for example, 0.1% means S=0.001.
• For each channel, A and P must be the wetted cross-sectional area and wetted perimeter at the stated flow depth, excluding the free surface from P.

Boundary hardening

BREAK_CLAIMED · SELF_FLAGGED

The specification has no stated validation for n=0 or negative slope. n=0 causes division by zero, while a signed negative slope makes the square-root argument invalid; both can produce undefined results unless rejected or assigned an explicit convention.

Errata and corrections

No applied erratum is attached to this unique-name record.

Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

{
  "inputs": {
    "system": "SI",
    "shape": "rectangular",
    "width_m": 3,
    "depth_m": 1,
    "mannings_n": 0.025,
    "slope": 0.001
  },
  "expected_outputs": {
    "hydraulic_area_m2": 3,
    "wetted_perimeter_m": 5,
    "hydraulic_radius_m": 0.6,
    "velocity_m_per_s": 0.899831,
    "discharge_m3_per_s": 2.69949
  },
  "working": "A=b y=3*1=3 m^2. P=b+2y=3+2(1)=5 m. R=A/P=3/5=0.6 m. V=(1/0.025)(0.6)^(2/3)(0.001)^(1/2). (0.6)^(2/3)=0.711378661 and sqrt(0.001)=0.0316227766, so V=40*0.711378661*0.0316227766=0.8998307 m/s, or 0.899831 m/s. Q=VA=0.8998307*3=2.699492 m^3/s, or 2.69949 m^3/s."
}

Related workflows

No source-defined multi-instrument workflow membership is recorded.

Sources and evidence

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

• VERIFIED_LEDGER.json · VERIFIED_CLEAN
• evidence-tranche6/tranche6-results.json
• BOUNDARY_HAZARD_CATALOG.json