Source: https://guthlabs.ai/docs/instruments/open-channel-flow-manning-s-equation/
instrument / verified-clean
# Open-Channel Flow — Manning's Equation
The current ledger marks this instrument verified clean within the source-bound verification corpus.
Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**
## Inspectable records
[01**Overview**Purpose and lifecycle]()[02**Mechanism**Method and assumptions]()[03**Implementation**Binding and validation]()[04**Qualification**Evidence and errata]()
## 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`