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| Scenario | Length (m) | Bottom width (m) | Depth (m) | Side slope (H:V) | Evap. (mm/day) | Area (m²) | Loss (m³/day) |
|---|---|---|---|---|---|---|---|
| Warm month (Direct) | 2000 | 3.0 | 1.2 | 1.5 | 7.5 | 13200 | 99.0 |
| Mild month (Pan × Kp) | 2000 | 3.0 | 1.2 | 1.5 | 6.0 × 0.70 = 4.2 | 13200 | 55.4 |
| Dry season (ET0 × Kc) | 2000 | 3.0 | 1.2 | 1.5 | 5.5 × 1.05 = 5.78 | 13200 | 76.3 |
Open-channel systems can lose meaningful volumes to evaporation during hot, dry, windy conditions. A daily depth of 6–10 mm/day across long reaches adds up quickly. A 2 km reach with 13,200 m² surface area and 7.5 mm/day evaporation loses about 99 m³/day, equal to roughly 1.15 L/s for budgeting, monitoring, and stakeholder reporting.
Use Direct depth when you have local open-water measurements. With pan records, multiply pan evaporation by Kp; typical Kp values are 0.60–0.85 depending on exposure. When ET0 is available, multiply by an open-water coefficient Kc; common Kc values are about 0.95–1.20 for exposed channels.
Evaporation depends on water-surface area, not wetted perimeter. If measured surface width is unknown, the calculator estimates trapezoidal surface width using W = b + 2zd. For b = 3.0 m, z = 1.5, and d = 1.2 m, W ≈ 6.6 m and A = W×L ≈ 13,200 m² for a 2,000 m reach.
Depth in mm/day is converted to meters per day by dividing by 1000. Daily volume loss is Vday = A×(E/1000) in m³/day. The tool converts to m³/s by dividing by 86,400 and to L/s by multiplying by 1,000. Over any period, Vperiod = Vday×days.
When flow rate is provided, the calculator reports loss as a percentage of delivered daily volume, which helps compare options across reaches and seasons. Export CSV/PDF outputs to document assumptions and run scenarios (different widths, depths, or periods). For reduction planning, consider operational measures like reducing exposed width during low-demand periods, and physical options such as windbreaks or partial shading on critical reaches. Combine evaporation with seepage estimates for a complete conveyance-loss balance.
It estimates evaporation loss from a canal water surface using an evaporation depth and surface area. It does not include seepage, leakage, or operational spill losses.
Use direct depth when you have local open-water measurements. Use pan data with Kp when only pan evaporation is available. Use ET0 with Kc when your weather source reports reference evapotranspiration.
Evaporation volume is proportional to water-surface area. A small width error over long lengths can change losses substantially, so use the measured surface width override whenever you can.
Common starting points are Kp = 0.70 and Kc = 1.05. For daily evaporation depth, many hot-season sites fall between 6 and 10 mm/day, but local data is always preferred.
Yes. Set the analysis period to the number of days in your month and enter a representative daily evaporation depth. For higher accuracy, run multiple scenarios for different weeks and sum the totals.
The calculator converts m³/day to m³/s by dividing by 86,400, then multiplies by 1,000 to report L/s. This helps compare evaporation loss with flow instrumentation readings.
Run the scenario, then download CSV for spreadsheets or PDF for quick sharing. Keep exports with your assumptions (method, widths, depths, period) to support reviews, audits, and future calibration.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.