Field Intake Test
Site: Plot A Date: 2026-07-23 Operator:
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Notes:
Documentation
Use these references when collecting data, checking assumptions, or interpreting results.
Formula guide
The depth-based calculation divides infiltrated depth by elapsed time. The volume-based calculation first converts volume over area into an equivalent water depth. Since one liter spread over one square meter equals one millimeter, metric normalization is direct and transparent.
Volume method: f = V / (A × t)
Cumulative infiltration: F = ΣΔD
An interval intake rate describes one observation period. An average intake rate describes the complete test. A basic intake rate should represent the stabilized late-stage rate. These values are related, but they are not interchangeable.
Field method guide
Single-ring infiltrometer
Drive one ring into the soil without disturbing the interior surface. Maintain a measured water head, record water additions, and note any visible leakage around the ring. The method is quick, but lateral flow can cause the apparent intake rate to exceed the true vertical rate.
Double-ring infiltrometer
Use the inner ring for measurements and the outer ring as a hydraulic buffer. Keep water levels similar in both rings. Record refill volumes or water-level decline at short intervals initially, then extend the interval as the rate stabilizes.
Mini-disk infiltrometer
Select the suction head recommended for the soil and instrument. Prepare a flat contact surface, avoid gaps beneath the disk, and record reservoir decline. Interpret results with the appropriate instrument geometry and tension-infiltration method.
Basin test
Level the test basin, measure its wetted area, apply water uniformly, and track depth changes. Protect the perimeter from overtopping. Basin tests represent ponded conditions and may produce different results from sprinkler application.
Furrow intake test
Measure inflow, outflow, advance time, recession time, furrow geometry, and wetted length. Intake is inferred from the water balance. Repeat furrows when field variability or flow instability is significant.
Border irrigation test
Record inflow hydrograph, water advance, cutoff, recession, field slope, border width, and length. Intake parameters should be evaluated together with surface-storage and runoff observations.
Rainfall simulator
Apply a known rainfall intensity over a measured plot. Record runoff initiation, runoff volume, and rainfall duration. The difference between applied water, runoff, and surface storage supports an event-scale infiltration estimate.
Ponded infiltration test
Maintain a constant or falling water head above the soil. Carefully measure water depth, temperature, cracks, macropores, and any boundary leakage. Ponded tests can emphasize preferential flow pathways.
Data-quality guide
Increasing cumulative time
Each observation time must be greater than the preceding time. Duplicate or decreasing times create zero or negative intervals and are rejected.
Short initial intervals
Use frequent readings during the first stage because intake commonly changes rapidly after wetting begins.
Stable ring head
Large differences in ponded depth can alter hydraulic gradients. Keep the prescribed head as constant as practical.
Undisturbed placement
Avoid smearing, cracking, or compacting the soil when installing equipment. Disturbance can dominate the measured response.
Representative location
Avoid wheel tracks, animal burrows, fertilizer bands, cracks, field edges, and unusual depressions unless those conditions are the study target.
Replicate tests
Spatial variability is normal. Use multiple tests and report median, range, and site conditions instead of relying on one location.
Temperature note
Water viscosity changes with temperature. Record water and soil temperature when comparing tests across seasons.
Antecedent moisture
Dry and wet starting conditions can produce very different early intake rates. Document recent rainfall and irrigation.
Macropore inspection
Cracks, root channels, worm holes, and gravel contacts may cause preferential flow. Note them before and after the test.
Leak check
Inspect ring walls and tubing. Water bypassing the measured area produces an artificially high intake estimate.
Steady-rate criterion
Do not call a rate steady merely because the last two numbers look similar. Evaluate several late readings and measurement precision.
Unit audit
Confirm that depths, volume, area, time, and application rate units match the selected controls before using the result.
Irrigation planning guide
Application rate is the depth of water delivered per unit time. When it exceeds the soil intake capacity, surface storage increases and runoff may begin. A design margin below the measured basic intake rate is therefore useful.
Sprinkler spacing and discharge can be converted to a nominal precipitation rate. Field uniformity, wind, pressure variation, nozzle wear, and overlapping patterns can create local rates above the average.
Drip systems apply water to a limited wetted area. A field-average application rate may appear low while the local rate beneath an emitter is high. Evaluate emitter discharge, spacing, soil texture, and wetted geometry together.
Surface irrigation depends on advance time, recession time, slope, roughness, field dimensions, inflow, and infiltration. A single intake number is useful, but full design normally requires a hydraulic surface-irrigation model.
Runoff estimates in this calculator are screening estimates. They assume that water applied above the calculated intake rate becomes runoff. Actual fields can temporarily store water in surface depressions or lose water through deep preferential pathways.
Net stored depth applies the selected efficiency after limiting gross infiltration by soil intake. Deep percolation is estimated when net stored depth exceeds the target depth. Root-zone storage capacity should be evaluated separately.
Pulse or cycle-soak irrigation can reduce runoff on slow-intake soils. Divide the required runtime into shorter events with rest periods, then verify actual performance in the field.
On sloping ground, erosion risk can become important before total runoff volume appears large. Reduce application rate, protect the surface, shorten run length, or use additional controls where concentrated flow develops.
Infiltration model guide
Kostiakov
The Kostiakov model represents cumulative infiltration as a power function of time. It usually fits early and intermediate observations well, but the derivative may approach zero at long times. Use it mainly within the measured time range.
Modified Kostiakov
The modified form adds a final-rate term. It often behaves more realistically for longer irrigation events because cumulative infiltration continues to increase approximately linearly after the transient stage.
Horton
The Horton model represents intake rate declining exponentially from an initial rate toward a final rate. This calculator fits the rate form and integrates it to compare cumulative infiltration.
Philip
The Philip approximation separates capillary sorptivity from a gravity-related term. It is useful for interpreting early infiltration, though the two-term form may not describe every soil throughout long tests.
Green-Ampt
Green-Ampt uses saturated conductivity, wetting-front suction, and water-content change. It provides a physically interpretable approximation with a sharp wetting front. Parameter quality strongly controls the result.
Model ranking
Models are ranked by cumulative-infiltration RMSE. R-squared, MAE, and standard error are also shown. A lower error does not guarantee that parameters are physically reasonable or transferable to another field.
Soil interpretation guide
Sand
Large pores usually permit rapid intake. Water storage per unit depth is often limited, so short and frequent irrigation may improve management.
Loamy sand
Intake remains relatively rapid. Surface sealing can reduce the rate when fine particles, traffic, or intense rainfall are present.
Sandy loam
Moderately rapid intake is common. Structure, organic matter, and compaction can move field results across a broad range.
Loam
Balanced texture can support moderate intake and useful storage. Tillage pans or surface crusts can substantially reduce performance.
Silt loam
The surface may seal under rainfall or sprinkler impact. Residue cover and aggregate stability are important for maintaining intake.
Clay loam
Intake is often slow to moderate. Shrinkage cracks may create a very high initial rate that later falls sharply.
Silty clay
Slow matrix intake and surface ponding are common. Cracks and preferential pathways can make short tests misleading.
Clay
Intake can be very slow after swelling, yet dry cracks may accept water quickly at first. Long observation periods are often necessary.
Frequently asked questions
What is soil intake rate?
It is the rate at which water enters the soil surface under specified test and hydraulic conditions.
Is intake rate the same as saturated hydraulic conductivity?
No. Intake rate is an observed surface flux. Saturated hydraulic conductivity is a material property used in flow equations.
Why is the first rate usually high?
Dry soil suction, open pores, and cracks can draw water quickly before the profile wets and flow paths change.
Which result should I use for sprinkler design?
Use a conservative basic or late-stage field rate, then apply a design margin and verify performance under the actual sprinkler pattern.
Can I estimate intake from soil texture?
Yes for screening, but texture alone cannot capture structure, compaction, crusting, moisture, cracks, and management history.
How many observations are needed?
Use enough readings to describe the rapid early decline and the later stabilized stage. Four is a minimum for simple fitting; more is preferable.
Why did a model fail to fit?
Non-increasing time, zero cumulative depth, noisy data, a short test, or incompatible model behavior can prevent a stable fit.
Why is runoff predicted immediately?
The entered application rate is above calculated intake capacity. Real surface storage may delay visible runoff.
Does the calculator account for depression storage?
No. The runoff screen assumes excess application becomes runoff and therefore remains conservative for short events.
Can I use refill volume instead of water-level drop?
Yes. Enter the test area and refill volume. Leave interval depth blank for those rows.
Why does area matter for volume readings?
The same water volume creates different equivalent depths over different surface areas.
What if both depth and volume are entered?
The calculator prioritizes interval depth. Leave it blank when you want the volume method used.
Should I include outer-ring volume?
Normally use inner-ring measurements for the calculated intake. The outer ring supports more vertical flow conditions.
Can this replace a laboratory conductivity test?
No. It is a field intake calculator and model-fitting aid, not a laboratory permeameter procedure.
How do cracks affect the result?
Cracks can create preferential flow and unusually high early intake. Record them and repeat after swelling when relevant.
How does compaction affect intake?
Compaction often reduces connected macropores and increases resistance near the surface or within traffic layers.
How does residue cover affect intake?
Residue can reduce raindrop impact, preserve aggregates, slow overland flow, and support biological pores.
Why record bulk density?
Bulk density is a useful compaction indicator and helps explain unusually slow intake, though critical values depend on texture.
What is sorptivity?
Sorptivity describes capillary-driven water uptake and appears as the square-root-of-time coefficient in the Philip model.
What is wetting-front suction?
It is an effective suction term used by Green-Ampt to represent capillary attraction at the advancing wetting front.
What does R-squared mean here?
It describes how much variation in observed cumulative infiltration is represented by the fitted predictions.
Should I choose the highest R-squared model?
Not automatically. Also inspect RMSE, residual behavior, parameter realism, and intended prediction duration.
Can a perfect fit still be wrong?
Yes. Few data points, overfitting, unit mistakes, or nonrepresentative conditions can produce misleadingly strong statistics.
What does basic intake rate mean?
It is the approximately stabilized late-stage intake rate used in many irrigation design procedures.
How long should a test run?
Continue until late readings stabilize for the intended design purpose. Fine soils often require longer tests than coarse soils.
Does slope change infiltration itself?
Slope mainly changes ponding, runoff, and opportunity time, though erosion and surface condition can indirectly change intake.
Can rainfall intensity be entered as application rate?
Yes. Select rainfall assessment and compare rainfall intensity with the calculated intake rate.
How is opportunity time calculated?
The calculator divides target depth by calculated intake rate as a simple screening estimate.
Does efficiency affect runoff?
In this calculator, runoff is controlled by application above intake. Efficiency affects estimated net stored depth.
How is deep percolation estimated?
It is the net stored depth above the target depth. Actual deep percolation also depends on root-zone storage and redistribution.
Can I save a test?
Yes. The save button stores the current form in browser local storage on that device.
Can I export data?
Yes. Observation rows export as CSV, and the complete form plus displayed results export as JSON.
How do I create a PDF?
Use Print or save PDF. Modern browsers can save the print layout as a PDF file.
Is the calculator mobile friendly?
Yes. Inputs stack responsively and observation tables can be horizontally scrolled on small screens.
Does the page require a database?
No. Calculation and browser saving work without a database.
Does it work on PHP 8.3?
Yes. The file uses PHP 8-compatible syntax and avoids deprecated dynamic behavior.
Are negative values accepted?
No. Relevant fields are constrained to nonnegative values, and invalid observation intervals are ignored.
Can I change units after entering data?
Yes, but observation depths and volumes are interpreted using the currently selected global units.
What does the safe rate represent?
It is 85 percent of the calculated intake rate, provided as a conservative planning margin.
Can I use the average rate as the final rate?
Only when the test is short and that limitation is clearly documented. Late-stage rate is usually more appropriate for runoff design.
Glossary
Application efficiency
The fraction of gross applied water estimated to become useful stored water.
Application rate
Water depth delivered per unit time by irrigation or rainfall.
Basic intake rate
The approximately stable late-stage rate after the transient wetting phase.
Bulk density
Dry soil mass divided by total bulk volume, commonly expressed in grams per cubic centimeter.
Cumulative infiltration
Total equivalent water depth entering the soil since the test began.
Deep percolation
Water moving below the intended storage or root-zone depth.
Depression storage
Water held temporarily in small surface depressions before runoff begins.
Hydraulic conductivity
A measure of the soil's ability to transmit water under a hydraulic gradient.
Infiltration
Movement of water from the surface into soil.
Intake opportunity time
The duration water is available to infiltrate at a location.
Interval rate
Average intake rate calculated over one observation interval.
Macropore
A large connected pore such as a crack, root channel, or worm passage.
MAE
Mean absolute error between observations and model predictions.
Ponding
Accumulation of water on the soil surface when supply exceeds intake or drainage.
Preferential flow
Rapid water movement through selected pathways instead of uniform matrix flow.
Residual
Observed value minus the corresponding model prediction.
RMSE
Root mean square error, which gives greater weight to larger model errors.
Runoff
Water leaving the evaluated surface area rather than infiltrating or remaining stored on the surface.
Sorptivity
A coefficient describing early capillary-driven uptake.
Surface crust
A dense surface layer formed by aggregate breakdown, sealing, or drying.
Wetting front
The transition zone between wetter soil above and drier soil below during infiltration.
Field audit checklist
Before field work
- Confirm the study objective and required reporting units.
- Select representative locations and planned replicates.
- Inspect rings, reservoirs, tubing, rulers, timers, and seals.
- Measure ring dimensions rather than relying only on nominal size.
- Prepare enough water for the expected duration and intake rate.
- Record recent rainfall, irrigation, tillage, and traffic history.
- Choose a safe area away from buried services or unstable ground.
- Prepare a field sheet or mobile data-entry plan.
- Verify that clocks and timers use the same reference.
- Plan how water temperature and weather will be recorded.
During installation
- Remove only loose residue that prevents sealing; document what was removed.
- Drive rings vertically and avoid rocking them.
- Protect the soil surface from impact during initial filling.
- Seal obvious gaps along ring walls without smearing the test surface.
- Measure exposed ring height and insertion depth.
- Document cracks, roots, gravel, biological pores, and surface crust.
- Set rulers or sensors where readings are repeatable.
- Use similar water levels in inner and outer rings when appropriate.
- Avoid stepping or kneeling near the active test area.
- Photograph the installed setup for the report.
During measurement
- Start timing at the defined wetting moment.
- Use short early intervals and longer later intervals.
- Record every refill volume and water-level reading immediately.
- Note spills, overtopping, leakage, or interrupted flow.
- Maintain the prescribed head within the allowed tolerance.
- Check whether the outer ring remains adequately supplied.
- Observe whether visible runoff or lateral seepage develops.
- Continue until the late-stage rate is acceptably stable.
- Mark any row that should be excluded and explain why.
- Repeat measurements that appear inconsistent when possible.
After measurement
- Check unit labels before transferring data.
- Plot cumulative infiltration and interval rate against time.
- Review late-stage stability rather than only the average.
- Compare replicate locations and identify outliers.
- Inspect the wetted profile if the study allows excavation.
- Document restrictive layers, cracks, roots, and depth of wetting.
- Choose model results based on statistics and physical reasonableness.
- Apply a conservative design margin for irrigation planning.
- Archive raw observations separately from corrected data.
- Include limitations and field conditions in the final report.