Sizing a Minimum HP Pump for Irrigating a 3.4-Acre MX Track from a 100-Foot Well

Calculating Water Requirements for Generator-Powered Irrigation

Determining the right pump size for irrigating a 3.4-acre motocross track using a generator requires calculating your water demand first, then matching a pump to your well's specific characteristics.

Water Volume Calculations

To apply ¼ inch of water across 3.4 acres:

• Total volume needed: 22,200 gallons
• For a 12-hour irrigation window: 1,853 gallons/hour = 31 GPM (gallons per minute)
• Adjust formula: 22,200 ÷ hours of operation ÷ 60 = required GPM

Why Pump Horsepower Can't Be Specified Yet

The required pump HP depends critically on the well's dynamic water level (pumping level), which won't be known until after drilling:

• If water rises to 20 feet below surface: lower HP needed
• If water stays at 80 feet down: significantly higher HP required
• Difference can mean 1 HP vs. 3+ HP for the same flow rate

Working With Your Well Driller

Provide your driller with:

1. Required GPM (e.g., 31 GPM for 12-hour cycle)
2. Desired operating pressure (typically 40–60 PSI for sprinklers)
3. Generator voltage (120V/240V) and capacity

The driller can then select a pump/motor combination that matches the well's actual yield and lift requirements. Consider a variable frequency drive (VFD) pump if your generator has limited surge capacity, as VFDs reduce starting current dramatically.