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Cutthroat Flume Calculator

Compute Skogerboe cutthroat flume free-flow discharge from throat width W, independent flume length L_f, and gage head Ha. Runs locally. Not a Parshall flume, not a thin-plate weir, not a broad-crested weir, not Manning, not Q=Av, and not an orifice.

Instant result
Result
—

Enter values to calculate.

Inputs—
Mode—
Formula—
Trust summary Engine tested · Source checked · 5/5 tests · Production surface contract 1/1 · v1.0.0
Input interpretation
Enter values to calculate.
Result
—
Model
Skogerboe cutthroat flume free-flow discharge or gage head. SI W, L_f, Ha, Q.
Scope
Skogerboe cutthroat free flow: Q_cfs = C Ha_ft^n; C=3.50 W_ft^{1.025} (L_f/3 ft)^{0.020}; n=1.56 (L_f/3 ft)^{0.026}; SI W, L_f, Ha, Q; C and n are reported, not inputs
Verification
Engine tested · 5/5 tests · Production surface contract 1/1 · Source checked · v1.0.0
Named expert review
Optional · Not performed
Sources
  • Skogerboe, G.V.; Hyatt, M.L.; England, J.D.; Johnson, J.R. — Design and Calibration of Submerged Open Channel Flow Measurement Structures, Part 3: Cutthroat Flumes — 3-ft family free-flow rating
  • ISO 80000-4 — Mechanics — Volume flow rate
Sources
Evidence
5 property · Production surface contract 1/1 · Artifact integrity PASS
Production
Embedded snapshot: STALE · Last attested schema matched 1.0.0 snapshot / local build · Semantic contract ✓ · Last attestation PASS · current evidence changed · re-attestation required · Public/cache ✓ · Origin ✓ · Live production status PASS (0 stale; 164 CURRENT) @ 2026-09-18T02:44:05.986Z
Semantic contract
PASS

Formulas

Core equations used by this calculator.

Skogerboe free flowQ_cfs = C Ha_ft^n
CoefficientC = 3.50 W_ft^{1.025} (L_f / 3 ft)^{0.020}
Exponentn = 1.56 (L_f / 3 ft)^{0.026}
iSI. Convert with 1 ft = 0.3048 m and 1 cfs = 0.028316846592 m³/s. Envelope L_f∈[0.4572 m, 2.7432 m], W∈[0.0508 m, 1.8288 m] with W < L_f, Ha∈[0.03048 m, 1.2192 m]. Submerged flow is out of scope. Do not send query v — that is calculation_version.

How to use

1

Enter throat width W

Cutthroat throat in metres. This is not weir span b or crest L.

2

Enter flume length L_f

Independent length. A Parshall flume has no free L_f; omit it there.

3

Enter gage head Ha or discharge Q

Give one, not both. Ha is the specified-gage head, not weir H.

Example calculations

Common configurations with formula and result.

ϟ

3 ft length, 1 ft throat, 1 ft Ha

L_f=0.9144 m, W=0.3048 m, Ha=0.3048 m

Q_cfs = 3.50 (1)^{1.56}
Q=3.50 cfs ≈ 0.09911 m³/s
ϟ

Invert Ha from that Q

L_f=0.9144 m, W=0.3048 m, Q≈0.09911 m³/s

Ha_ft = (Q_cfs / C)^{1/n}
Ha=0.3048 m

Cutthroat Flume calculator specification

Version 1.0.0 · Engine tested

Calculation status

Review policy · Evidence

Definition
Skogerboe cutthroat flume, free flow. No diverging section, so flume length L_f is independent. Q_cfs = C Ha_ft^n with C = 3.50 W_ft^{1.025} (L_f/3 ft)^{0.020} and n = 1.56 (L_f/3 ft)^{0.026} (3-ft family). Inputs and result are SI (W, L_f, Ha in m, Q in m³/s). Ha is the specified-gage upstream head, not weir crest head H. C and n are reported, not inputs. Not Parshall 4 W_ft Ha^{1.522 W^{0.026}}, not thin-plate (2/3) C_d L √(2g) H^{3/2}, not broad-crested (2/3)^{3/2} b √g H^{3/2}, not Manning n, not Q=Av, not orifice, not submerged Hb.
What it calculates
Skogerboe cutthroat flume free-flow discharge or gage head. SI W, L_f, Ha, Q.
Inputs
  • mode?
  • W
  • L_f
  • Ha | Q
Outputs
  • Q
  • Ha
  • W
  • L_f
  • n
  • C
  • mode
  • model
Formula
Q_cfs = C Ha_ft^n; C = 3.50 W_ft^{1.025} (L_f/3 ft)^{0.020}; n = 1.56 (L_f/3 ft)^{0.026}
Assumptions
  • Skogerboe cutthroat free flow: Q_cfs = C Ha_ft^n; C=3.50 W_ft^{1.025} (L_f/3 ft)^{0.020}; n=1.56 (L_f/3 ft)^{0.026}; SI W, L_f, Ha, Q; C and n are reported, not inputs
  • No diverging section; L_f is independent flume length, not weir crest L; W < L_f; L_f∈[0.4572 m, 2.7432 m]; W∈[0.0508 m, 1.8288 m]; Ha∈[0.03048 m, 1.2192 m]
  • Not Parshall 4 W_ft Ha^{1.522 W^{0.026}}, not thin-plate weir, not broad-crested (2/3)^{3/2} √g, not Manning n, not Q=Av, not orifice, not submerged Hb
Units
  • SI; W, L_f, and Ha in m; Q in m³/s; n and C dimensionless (C in cfs units before SI conversion)
Boundary conditions
  • missing W, L_f, Ha, or Q when required → MISSING_REQUIRED_INPUT
  • Ha and Q together, weir H/L/b, Manning n/R/S, orifice A/d/D/Δp, Q=Av v, yc/q/Fr/g, Cd, Hb, W_ft, kind=parshall → MIXED_INPUT_ENCODING
  • L_f outside [0.4572, 2.7432] m, W outside [0.0508, 1.8288] m, W ≥ L_f, or Ha outside [0.03048, 1.2192] m → VALUE_OUT_OF_RANGE
  • mode=rectangular|thin-plate|broad-crested|parshall or unknown mode → MIXED_INPUT_ENCODING or INVALID_MODE
Example
L_f=0.9144 W=0.3048 Ha=0.3048 → Q≈0.09911
Validation cases

4 published on this page · 5/5 tests · Production surface contract 1/1 · View evidence

  • L_f=0.9144 W=0.3048 Ha=0.3048 → Q = 3.50 cfs ≈ 0.09911 m³/s
  • W=0.3048 Ha=0.3048 → MISSING_REQUIRED_INPUT (L_f)
  • L_f=0.9144 W=0.3048 Ha=0.3048 H=0.3048 → MIXED_INPUT_ENCODING
  • mode=parshall L_f=0.9144 W=0.3048 Ha=0.3048 → MIXED_INPUT_ENCODING
Sources
  • Skogerboe, G.V.; Hyatt, M.L.; England, J.D.; Johnson, J.R. — Design and Calibration of Submerged Open Channel Flow Measurement Structures, Part 3: Cutthroat Flumes — 3-ft family free-flow rating
    Supports: C=3.50 W_ft^{1.025} and n=1.56 at L_f=3 ft; L-scaled n and C; not a Parshall 4 W rating
  • ISO 80000-4 — Mechanics — Volume flow rate
    Supports: Q is volume flow; W, L_f, and Ha are lengths
Calculation version
1.0.0

Background

Interpretation and common distinctions.

Compute cutthroat flume free-flow discharge from throat width, independent flume length, and specified-gage head.

Supported and not supported

Supported — Skogerboe 3-ft-family free-flow Q from W, L_f, and Ha · invert Ha from Q · API physics.fluid.cutthroat_flume

Not supported — Parshall (no independent L_f), thin-plate weir, broad-crested weir, Manning n, Q=Av, orifice, submerged Hb/Ha

Agent / API notes

Capability id: physics.fluid.cutthroat_flume · tool id: cutthroat-flume · pin 1.0.0.

{ "W": 0.3048, "L_f": 0.9144, "Ha": 0.3048 }

Invert: { "mode": "head", "W": 0.3048, "L_f": 0.9144, "Q": 0.09911 }. Errors: MISSING_REQUIRED_INPUT, INVALID_NUMBER, VALUE_MUST_BE_POSITIVE, VALUE_OUT_OF_RANGE, MIXED_INPUT_ENCODING, INVALID_MODE.

Calculator URL stays /calc/physics/cutthroat-flume. There is no /calc/fluid.

Other calculators in this family: Parshall flume, Broad-crested weir, Thin-plate weir, Manning formula, Flow rate .

Q Parshall flume › Q Broad-crested weir › Q Thin-plate weir › Q Manning formula › Q Flow rate ›
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Frequently asked questions

Key distinctions behind the calculation.

Is this a Parshall flume?

No. Parshall has a standard diverging section, so length is not free. USBR 1–8 ft Q_cfs=4 W_ft Ha_ft^n is /calc/physics/parshall-flume. Sending kind=parshall here is MIXED_INPUT_ENCODING. Omitting L_f is MISSING_REQUIRED_INPUT and points at that page. At W=0.3048 m and Ha=0.3048 m a 3 ft cutthroat reports ≈0.09911 m³/s, not Parshall ≈0.11327 m³/s.

Is this a thin-plate weir?

No. Thin-plate Q=(2/3) C_d L √(2g) H^{3/2} is /calc/physics/weir-discharge. Sending H or crest L here is MIXED_INPUT_ENCODING. L_f is flume length, not weir crest L.

Is this a broad-crested weir?

No. Rectangular broad-crested Q=C_d (2/3)^{3/2} b √g H^{3/2} is /calc/physics/broad-crested-weir. Sending b, H, Cd, or g here is MIXED_INPUT_ENCODING.

Is this the Manning formula?

No. Manning is uniform open-channel flow from n, A, R, and S at /calc/physics/manning-formula. Sending n, R, or S is MIXED_INPUT_ENCODING. This page reports the rating exponent n; it is not an input.

Is this Q = A·v?

No. Volumetric flow from a given area and velocity is /calc/physics/flow-rate. Sending A or v is MIXED_INPUT_ENCODING.

Is this an orifice?

No. A hole under head or a pipe orifice plate is /calc/physics/orifice-discharge. Sending d, D, or Δp is MIXED_INPUT_ENCODING.

Can I send submerged Hb?

No. This seed is free flow only. Submerged Hb/Ha is MIXED_INPUT_ENCODING.

Is this a sluice gate?

No. A free-flow undershot sluice with Swamee C_d from a/y1 is /calc/physics/sluice-gate. Sending kind=sluice here is MIXED_INPUT_ENCODING.

Where does this run?

Locally in the browser by default. REST and MCP call the same fluid-engine cutthroatFlume wrapper.