Calculator inputs
Choose what you want to solve for. Provide the known values. For depth-based sizing, enter water depth and efficiencies.
Example data table
Typical planning checks for canal sizing and field depth. Use these as verification cases while setting up your project inputs.
| Scenario | Area (ha) | Discharge (m3/s) | Base period (days) | Duty (ha per m3/s) | Delta (mm) |
|---|---|---|---|---|---|
| Canal check | 120 | 2.00 | 120 | 60.00 | 17280.00 |
| Branch reach | 75 | 1.20 | 90 | 62.50 | 12441.60 |
| Depth-based sizing* | 60 | 0.70 | 60 | 85.71 | 6048.00 |
| Intermittent supply* | 40 | 0.35 | 45 | 114.29 | 3402.00 |
Formula used
- D = A / Q, where D is duty (ha per m3/s), A is area (ha), and Q is discharge (m3/s).
- Delta (m) = 8.64 x B / D, where B is base period (days).
- Q = (Area(m2) x GrossDepth(m)) / Time(s), with Time = B x HoursPerDay x 3600.
- GrossDepth = NetDepth / (Ec x Ea), where efficiencies are entered as percentages.
- NetDepthAdjusted = max(0, NetDepth - EffectiveRainfall).
How to use this calculator
- Select the target value: duty, discharge, area, or depth.
- Enter known values with correct units and realistic base period.
- For depth-based sizing, input net depth and efficiencies.
- Adjust operating hours and rotation factor for supply schedules.
- Click Calculate, then export CSV or PDF for records.
Technical note for irrigation duty planning
1) Typical duty ranges used in projects
Duty expresses how much land a steady flow can serve: D = A / Q. For gravity-fed canals, duty commonly falls between 800 and 3,000 ha per m3/s, depending on climate, crop mix, and losses. For site irrigation supplied by pumps, duty may be lower, often 50 to 400 ha per m3/s, because flows are higher for smaller command areas.
2) Base period and operating schedule impacts
Base period is the irrigation window in days. A crop stage might use 30–60 days, while a full season commonly spans 90–150 days. If supply is not 24 hours/day, the same seasonal demand requires higher discharge. This calculator converts days and hours into total operating time in seconds for consistent flow calculations.
3) Depth, rainfall, and efficiencies
Depth (Delta) represents the seasonal depth of water over the field. Typical planning depths range from 300–900 mm, but the value depends on soil, crop, and irrigation method. Effective rainfall is subtracted from net depth. Conveyance and application efficiencies are multiplied to obtain overall efficiency. For early feasibility, many teams assume 0.60–0.85 overall efficiency.
4) Quick verification with a worked check
Example: If A = 120 ha and Q = 0.06 m3/s, then duty is D = 2,000 ha per m3/s. With B = 120 days, the classic depth relation gives Delta = 8.64 × 120 / 2,000 = 0.518 m (about 518 mm). If overall efficiency is 0.70, gross depth becomes about 740 mm.
5) Reporting and documentation
Use CSV exports for quantity takeoffs and design logs, and PDF exports for approvals and tender files. Always document the unit basis (ha, acre, L/s, or m3/s), assumptions for efficiencies, and whether the supply is continuous or rotational. This improves traceability during construction audits and commissioning reviews.
FAQs
1) What does “duty” mean in this calculator?
Duty is the command area supported per unit flow: D = A / Q. Here it is reported as hectares per cubic meter per second, so larger duty means a smaller flow is needed for a given area.
2) Why does the Delta value sometimes look very large?
Large Delta occurs when duty is small or base period is long. Check that discharge units are correct and that duty reflects your system scale. Canal duties are often much higher than pumped-site duties.
3) How are efficiencies applied?
Overall efficiency equals conveyance efficiency times application efficiency. Net depth is divided by this overall efficiency to estimate gross depth, which increases the required flow for the same field demand.
4) What is effective rainfall and how is it used?
Effective rainfall is the portion of rain that contributes to crop water use. The calculator subtracts it from net depth, never allowing the adjusted net depth to fall below zero.
5) When should I use the rotation factor?
Use rotation factor when supply is intermittent or shared by turns. A value below 1 indicates reduced availability. The calculator adjusts discharge sizing so the same seasonal volume can be delivered in the available time.
6) Can I work in liters per second and acres?
Yes. Enter discharge in L/s and area in acres, and the calculator converts them internally to m3/s and hectares. Always confirm the displayed converted results before exporting reports.
7) Which mode should I choose for design checking?
For canal or pump sizing, use Discharge mode with depth, efficiencies, and operating hours. For quick feasibility, Duty mode and Delta mode are useful to cross-check whether assumptions align with the project basis.