Siphon Tube Irrigation & Flow per Tube & Set Volume
Sizes furrow flow
Enter tube diameter, the head over the bund, the number of tubes and set time to get the flow per tube, the total flow and the water delivered per set — so you size the furrow set right.
Enter your siphon set
Next: run 20 tubes (~33 L/s) for 30 min to apply 59.4 m³; prime each tube and match the set to your furrow length/soil.
Flow uses Q=Cd·A·√(2gH); worn/partly-blocked tubes and low head reduce it — measure with a bucket to confirm.
Siphon tubes — key facts
- Flow per tube
- Q = Cd · A · √(2gH)
- Cd
- ≈ 0.6–0.65
- Driven by
- tube size & head
- Flow vs diameter
- rises with diameter²
- Flow vs head
- rises with √head
- No bund cut
- water drawn over the wall
- Each tube
- primed before flowing
- Privacy
- Runs in your browser; nothing uploaded
Water over the bund, not through it
Siphon tubes are one of the neatest tricks in surface irrigation: a short curved pipe lifts water over the field-channel wall and into a furrow without ever breaching the bund. Prime the tube, drop the end in the furrow, and gravity does the rest. The flow through each tube follows the orifice equation — Q = Cd · A · √(2gH) — so it depends on the tube's size and the head of water standing in the channel above the outlet.
This tool turns those into numbers — the flow per tube in L/s, the total set flow, and the water delivered per tube and per set — from the diameter, head, number of tubes and run time you enter. Prime each tube, match the set to the furrow length and soil intake, and feed the water-per-set figure into your plan. Pair it with the Furrow Irrigation, Channel Flow and Pump Run Time tools to size the whole system.
Size each tube
Flow per tube from diameter and head.
Balance the set
Total flow against your channel capacity.
No breaching bunds
Tubes draw water cleanly over the wall.
Match the soil
Water per set to suit furrow length & intake.
Frequently Asked Questions
What is siphon tube irrigation?+
It is a surface-irrigation method where short curved tubes draw water over the wall of a field channel into the furrows, without cutting or breaching the bund. Each tube is primed to start the siphon, and water then flows by gravity from the higher channel into the lower furrow as long as the head difference lasts. It is simple, cheap and gives even control of furrow flow.
How is the flow per tube calculated?+
It uses the orifice equation Q = Cd · A · √(2gH), where Cd is the discharge coefficient (about 0.6–0.65), A is the tube's cross-sectional area, g is gravity and H is the head — the height of water in the channel above the furrow outlet. Bigger tubes and more head give more flow. Multiply by the number of tubes for the total set flow.
What is the head and why does it matter?+
The head is the vertical difference between the water level in the channel and the discharge end of the tube. It is the driving force of the siphon: more head means faster flow through each tube. Because flow rises with the square root of head, doubling the head increases flow by about 40%, not 100%.
How does tube diameter change the flow?+
Flow scales with the tube's cross-sectional area, which goes up with the square of the diameter, so a small increase in diameter is a large increase in flow. A 50 mm tube delivers roughly four times the flow of a 25 mm tube at the same head. Choose the size to match the furrow length and soil intake.
How many siphon tubes should I run at once?+
Run as many as deliver a non-erosive stream to each furrow without overtopping it, matched to the flow your channel can hold. The total set flow should advance water down the furrows in a reasonable time, then be cut back. The tool's total flow helps you balance tubes against channel capacity.
How do I prime a siphon tube?+
Submerge the whole tube in the channel to fill it with water and expel the air, cap or block the discharge end, lift it over the bund and release it into the furrow so the water column starts the siphon. Once flowing, it continues on its own. Tubes that lose prime have sucked air — re-submerge and restart.
How long should a set run?+
Long enough for water to reach the furrow end and infiltrate to the root zone, then stop to avoid deep percolation and runoff. The set time depends on furrow length, slope, soil intake and the flow you set. The tool reports water per tube and per set so you can match the volume to the soil's needs.
Does it work for any tube or area unit?+
Yes — enter the tube diameter in millimetres, the head in centimetres and the set time in your units, for any number of tubes. The flow and volume outputs apply to whatever crop and furrow layout you irrigate; just feed the water-per-set figure into your field water plan.
Are the figures exact?+
They are sound planning estimates from the orifice equation. The real discharge coefficient varies with tube shape, entry condition and how clean the tube is, and the head changes as the channel level falls. Calibrate by timing how long a tube takes to fill a known bucket, and adjust your flow against the field.
How does this fit my irrigation plan?+
The water-per-set figure is the depth and volume you apply each irrigation, which feeds straight into furrow design and your water budget. See the Furrow Irrigation, Channel Flow and Pump Run Time calculators to size the furrows, the supply channel and the pump that fills it.