Calculator inputs
Use the responsive grid below. Large screens show three columns, smaller screens show two, and phones show one.
Example data table
| Case | Method | Width (m) | Opening (m) | Upstream head (m) | Tailwater (m) | Coefficient | Openings | Gross discharge (m³/s) |
|---|---|---|---|---|---|---|---|---|
| Outlet A | Sluice / Orifice Turnout | 0.75 | 0.45 | 1.05 | 0.20 | 0.62 | 1 | 0.9555 |
| Outlet B | Sharp-Crested Rectangular Weir | 1.20 | 0.00 | 0.35 | 0.05 | 0.62 | 1 | 0.4394 |
| Outlet C | Broad-Crested Turnout | 1.50 | 0.00 | 0.42 | 0.15 | 1.70 | 1 | 0.7020 |
Formula used
1) Sluice or orifice turnout
Free flow: Q = Cd × A × √(2gH)
Submerged flow: Q = Cd × A × √(2gΔH)
2) Sharp-crested rectangular weir
Q = (2/3) × Cd × be × √(2g) × H3/2, where be = b − 0.1nH
3) Broad-crested turnout
Q = Cw × b × H3/2
4) Applied adjustments
Velocity head: hv = Va2 / 2g
Net discharge: Qnet = Q × (1 − loss%)
Design discharge: Qdesign = Qnet / safety factor
Variables: Q discharge, Cd or Cw coefficient, A area, b width, be effective width, H head, ΔH differential head, g gravity, n contractions.
How to use this calculator
Choose the turnout type that best matches your control structure.
Enter the physical width, measured head, and the proper coefficient.
For sluice flow, also enter opening height and gate opening ratio.
Add losses and a safety factor if you need a conservative design value.
Submit the form to view discharge, hydraulic details, and the head versus discharge graph above the form.
FAQs
What is canal turnout discharge?
It is the flow rate diverted from a canal through a turnout structure. Engineers use it to size gates, evaluate irrigation delivery, and check operating capacity.
Which method should I select?
Choose sluice for gated openings, sharp-crested weir for thin-crested overflow control, and broad-crested when water passes over a wider crest with stable approach conditions.
Why is the coefficient important?
The coefficient captures contraction, approach effects, energy loss, and real structure behavior. Field calibration or local standards usually give more reliable values than generic assumptions.
How does tailwater affect discharge?
Higher downstream water can drown the structure, reduce available head, and lower discharge. The calculator flags potentially drowned conditions where detailed review may be needed.
Why include approach velocity?
Approach velocity adds velocity head to the control section. That slightly changes effective head and improves estimates when approach flow is not negligible.
What does design discharge mean here?
Design discharge is the net flow after deducting losses and applying the safety factor. It offers a more conservative value for planning and checking turnout performance.
Can I use this for field checks?
Yes, it works well for quick assessments, design screening, and comparison studies. Final designs should still follow local irrigation criteria, calibration data, and site-specific hydraulics.
What units does this file use?
Inputs are in meters and meters per second. Outputs are shown in cubic meters per second, liters per second, cusecs, and gallons per minute.