Flood Drain Timer Calculator

1. Choose Flow-based for quick setup using pump and drain rates.
2. Enter a target volume, or leave it blank to derive from bed size.
3. Set a void fraction that matches your growing media.
4. Pick an active window, then set cycles per day or a fixed interval.
5. Use a safety factor to cover line losses and real-world variation.
6. Press Calculate and copy the ON and OFF values to your timer.
7. Download CSV or PDF to save the schedule and results.
8. If you already tested, select Measured times and enter observed minutes.

1) Purpose of a flood drain timer

Flood and drain irrigation cycles deliver water and oxygen in repeated pulses. A timer helps keep media moisture consistent, reduces root stress, and prevents waterlogging. This calculator converts bed geometry, media void fraction, and measured flow rates into practical ON and OFF settings you can enter on a controller.

2) Data that drives accurate timing

Timing accuracy depends on three measurable inputs: water volume per cycle, pump delivery rate, and drain rate. If you do not know the target volume, the calculator estimates it from bed length, width, flood depth, and void fraction. For most coarse media, void fraction is commonly 30–45%.

3) Interpreting ON and OFF results

Pump ON is the flood duration needed to move the target liters into the bed. Pump OFF includes soak, drain, and rest. The safety factor increases flood and drain time to cover head loss, partially blocked emitters, or seasonal viscosity changes. If cycle duration exceeds your spacing, the schedule will run back-to-back inside the active window.

4) Scheduling within an active window

Use an active window to restrict cycling to daylight or to periods when temperature and evapotranspiration are highest. You can distribute a set number of cycles per day or use a fixed interval in minutes. The schedule preview lists pump ON start and end times, plus drain and rest completion markers to help you validate overlap and recovery time.

5) Commissioning and continuous improvement

After installation, run a field test and record observed flood and drain minutes. Switching to measured mode improves reliability because it captures real plumbing behavior and media compaction. Track water exchanged per day, and if you enter pump watts, monitor energy use to compare efficiency after maintenance or pump upgrades.

1) What is void fraction and why does it matter?

Void fraction is the open space in media that can hold water. Higher void fraction increases cycle volume, so flood and drain times increase for the same bed dimensions.

2) Should I use flow-based or measured mode?

Use flow-based mode for initial setup when you know pump and drain rates. Use measured mode after a test run to lock in real flood and drain minutes for better reliability.

3) How do I choose a safety factor?

Start with 10%. Increase if you see incomplete flooding, slow drainage, or long pipe runs. Reduce only after repeated tests show stable performance across different temperatures.

4) Why does the calculator warn about back-to-back cycles?

If your full cycle duration is longer than the cycle spacing, the next cycle cannot start on time. The schedule shifts to start immediately after rest ends to keep timing realistic.

5) How many cycles per day are typical?

Many systems use 4–10 cycles during daylight, but it varies with crop, climate, and media. Use shorter, more frequent cycles in warm conditions and longer rests in cool periods.

6) Can I estimate energy cost with this tool?

Yes. Enter pump watts and electricity cost per kWh. The calculator multiplies pump runtime by power to estimate kWh, then applies your rate to estimate operating cost.

7) What if my bed floods unevenly?

Check distribution, levelness, and clogged lines. Increase safety factor, reduce flood depth, or slow the pump if channeling occurs. Then retest and update measured times for stability.