Pump Delivery Rate
This is the flow the installed pump can move through the piping system. It may be limited by the pump, pipe diameter, lift, pressure requirements, filters or electrical supply.
Palm Tree Energy • Rural Water Infrastructure
Alfalfa Well Watering Capacity Assessment
Estimate whether your well, storage tank, pumping schedule and irrigation system can support the water demand of an alfalfa field.
Well and Irrigation Planning
Determine Whether Your Water System Can Support the Acreage
Growing alfalfa on a rural property requires more than selecting a pump with a high nameplate flow rate. The complete system must be evaluated, including the sustainable well recovery rate, allowable pumping hours, storage capacity, booster-pump output, irrigation efficiency and seasonal crop-water demand.
This assessment tool provides a preliminary comparison between estimated sustainable water supply and estimated alfalfa irrigation demand. It can help identify whether the property may have adequate capacity or whether additional testing, storage or infrastructure improvements should be considered.
Planning principle: A storage tank can supply
short-term flow and reduce pump cycling, but it does not create a
new daily water source. Long-term production is controlled primarily
by the sustainable well yield and the number of hours the well can
safely operate.
Interactive Planning Tool
Well Watering Capacity Calculator
Enter the known system information below. The calculator compares sustainable daily water production with estimated irrigation demand.
Alfalfa Water-Supply Assessment
Results are preliminary planning estimates and are not a substitute for a well test, irrigation design or agronomic evaluation.
1
Well and Pump Information
Actual flow delivered by the installed well pump.
Leave blank if unknown. A professional well test is preferred.
Maximum planned operating time within each 24-hour period.
Enter usable volume, not necessarily the tank’s full nameplate size.
2
Field and Crop-Water Assumptions
Select a local planning value based on climate and ET data.
Number of days over which the seasonal demand is supplied.
Lower efficiency requires more pumped water to meet crop demand.
3
Optional Delivery-System Check
Used to estimate how long the storage tank can support irrigation flow.
Retaining a reserve can help protect against low-water conditions.
Assessment Results
Governing sustainable flow
15 GPM
Lower of pump delivery and reported well recovery.
Sustainable daily well production
10,800 gal/day
Storage is not added as recurring daily production.
Estimated gross irrigation demand
36,206 gal/day
Crop demand adjusted for selected irrigation efficiency.
Average daily surplus or deficit
−25,406 gal/day
Estimated daily production is below estimated demand.
Usable storage buffer
4,000 gallons
Approximately 1.7 hours at 40 GPM without incoming well water.
Additional Capacity May Be Required
The calculator uses 325,851 gallons per acre-foot. Actual
crop demand, effective rainfall, soil-water storage,
irrigation losses, system pressure, well drawdown and
seasonal variation are not fully modeled.
Capacity Fundamentals
Three Numbers That Must Be Evaluated Separately
Pump flow, sustainable well yield and storage capacity perform different functions and should not be treated as the same measurement.
Sustainable Well Yield
This is the rate the well and aquifer can support over the intended operating period without unacceptable drawdown or pumping the well below a safe operating level.
Usable Storage
Storage allows a low-flow well to fill a tank gradually while an irrigation or booster pump draws water at a higher rate for a limited period. The tank does not increase the aquifer’s yield.
Field Assessment Manual
How to Evaluate an Existing Rural Water System
Gather the information in sequence so the complete water-production and delivery system can be reviewed.
1
Gather Information About the Existing System
- Well depth and static water level, when known.
- Pumping water level and drawdown during operation.
- Measured sustainable well recovery or production rate.
- Well-pump make, model, horsepower and actual flow.
- Daily pumping schedule and electrical-source limitations.
- Tank nameplate volume and estimated usable volume.
- Booster-pump flow rate, pressure and duty cycle.
- Irrigation-zone flow, pressure and application method.
- Existing domestic, livestock and other property water use.
2
Establish Sustainable Daily Water Supply
The governing flow should ordinarily be the lower of the pump’s actual delivery rate and the well’s sustainable recovery rate.
Sustainable daily supply = governing GPM × 60 × safe pumping hours per day
For example, a sustainable flow of 15 GPM operated for 12 hours produces approximately 10,800 gallons during that day.
3
Estimate Seasonal Alfalfa Water Demand
Alfalfa water use varies by location, temperature, wind, growing-season length, rainfall, cutting schedule and soil conditions. Use local evapotranspiration information and agricultural guidance whenever available.
Net seasonal gallons = acres × acre-feet per acre × 325,851
Gross pumped water = net seasonal gallons ÷ irrigation efficiency
Average irrigation-day demand = gross pumped water ÷ irrigation-season days
The calculated daily number is a seasonal average. Peak summer demand may be materially higher than the average.
4
Evaluate Storage and Irrigation Flow
A storage tank allows the well to operate at a relatively steady rate while a booster pump supplies the higher instantaneous flow required by sprinklers or irrigation zones.
Tank-only runtime in minutes = usable storage gallons ÷ booster-pump GPM
Actual runtime can be longer when the well continues filling the tank while irrigation is operating. Tank drawdown, reserve level and pump controls should be included in the design.
5
Compare Sustainable Supply With Demand
| Item | Question to Answer |
|---|---|
| Sustainable well production | How many gallons can the well reliably produce each day? |
| Crop-water demand | How many gallons are required during the irrigation season? |
| Peak-day capacity | Can the system serve hotter and windier periods? |
| Storage buffer | How long can the tank serve the irrigation pump? |
| Delivery capacity | Can the piping and booster pump maintain required flow and pressure? |
| Other property demand | Is domestic, livestock and fire-reserve water protected? |
6
Consider System Improvements
- Perform a professional well-production and drawdown test.
- Install a flow meter to track actual production and use.
- Add storage to improve buffering and pump scheduling.
- Separate irrigation storage from domestic or fire reserves.
- Improve irrigation distribution uniformity.
- Divide acreage into manageable irrigation zones.
- Use soil-moisture monitoring and weather-based scheduling.
- Review the well pump, booster pump, controls and electrical supply.
- Reduce irrigated acreage when sustainable supply is insufficient.
Field Measurements
Basic Ways to Measure Pump Flow
Measurement should be completed safely and without allowing pumps to run dry or operate outside their intended pressure range.
Known-Volume Tank Fill Test
- Identify a known change in tank volume.
- Turn off other water uses during the test.
- Operate the well pump and start a timer.
- Measure the minutes required to replace the known volume.
- Divide gallons filled by elapsed minutes.
GPM = gallons filled ÷ minutes
Example: 500 gallons filled in 25 minutes equals approximately
20 GPM.
Timed Container Test
- Use a container with a verified volume.
- Run the outlet at its normal operating condition.
- Measure the number of seconds required to fill it.
- Convert the result to gallons per minute.
GPM = gallons ÷ (seconds ÷ 60)
Example: A 5-gallon container filled in 15 seconds indicates
approximately 20 GPM at that outlet.
Important: A short tank-fill or bucket test measures
flow at the time of the test. It does not necessarily establish the
sustainable long-duration production of the well. A proper well test
evaluates pumping level, drawdown and recovery over time.
Local Planning Information
Use Local Weather and Irrigation Data
Local evapotranspiration and agricultural information provide a stronger basis than a single statewide water-use assumption.
California CIMIS
The California Irrigation Management Information System provides weather-station information, reference evapotranspiration data and spatial reports that can assist with irrigation scheduling.
Visit California CIMIS →Crop ET and Irrigation Efficiency
Reference evapotranspiration is ordinarily adjusted using an appropriate crop coefficient. Effective rainfall, soil-water storage and irrigation efficiency must also be considered when estimating the amount of water that must be pumped.
Consult a qualified crop adviser, irrigation designer or local agricultural extension specialist for site-specific values.
Palm Tree Energy
Rural Energy, Well-Pump and Water-Infrastructure Support
Palm Tree Energy assists with the electrical and energy infrastructure behind rural wells, storage tanks, booster pumps, irrigation systems, generators, solar power and battery storage.