infiltrometer

An infiltrometer is an instrument used to measure the rate at which water infiltrates into soil. It is widely used in hydrology and soil science to estimate infiltration capacity, hydraulic conductivity, and related properties that influence irrigation efficiency, drainage design, flood forecasting, and soil water balance.

Several infiltrometer designs are commonly employed. Constant-head infiltrometers maintain a steady water head above the soil surface, allowing infiltration rate to be inferred from the inflow during a fixed time. Falling-head infiltrometers allow the water head to decline while recording infiltration, from which the rate is calculated. The double-ring infiltrometer uses two concentric rings to isolate the infiltrating area from lateral flow, improving measurement accuracy on field soils. Tension or mini-disk infiltrometers create suction at the soil surface to measure infiltration under unsaturated conditions.

In practice, the infiltration rate is computed as the volume of water entering the soil divided by the infiltrated area and time. Data are often plotted as cumulative infiltration versus time or as infiltration rate versus time, and soil properties such as hydraulic conductivity are inferred through soil water balance or infiltration models. Measurements can be affected by antecedent moisture, soil crusting, compaction, roughness, and heterogeneity, so careful setup and calibration are important.