infiltrometry

Infiltrometry is the measurement of the rate at which water infiltrates into a soil or porous medium, as a function of time. It yields quantitative information on soil hydraulic properties such as infiltration capacity and, under some models, saturated hydraulic conductivity. It is used to characterize infiltration characteristics for agriculture, hydrology, and engineering applications.

Field infiltrometers, especially the double-ring type, are commonly used. The inner ring receives water while the outer ring reduces lateral flow between rings. Tests can operate under constant-head or falling-head conditions. In constant-head setup, the water height is maintained; in falling-head tests, the head declines as infiltration proceeds. The procedure generally involves placing the rings on a prepared soil surface, filling with water, and recording cumulative infiltration over time to compute an average rate. Laboratory equivalents use small permeameters or sandbox devices.

Data are analyzed by plotting cumulative infiltration versus time and fitting models such as Horton, Green–Ampt, or Philip. The infiltration rate typically declines with time as the soil wets and suction decreases. Parameters such as initial rate, steady-state rate, and infiltration capacity can be estimated, along with estimates of hydraulic properties from model fitting.

Applications include irrigation design, drainage assessment, erosion risk evaluation, and hydrological modeling. Limitations include soil heterogeneity, surface roughness, depth to a restrictive layer, macropores, vegetation, and the scale of measurement. Results are most representative of the sampled area and conditions, and standardized protocols are used to enable comparisons.