Berm Method for Quantification of Infiltration at the Plot Scale in High Conductivity Soils

Measuring infiltration at the plot scale is difficult, especially for high hydraulic conductivity soils. At the plot scale, the infiltration rate is usually calculated by comparing surface runoff to rainfall. Direct measurement of infiltration beyond the point scale is typically limited to locations where land forming (e.g., infiltration pond) has been performed or fields with basin irrigation systems. The standard method for field measurement of point-scale infiltration is the double ring infiltrometer, which is limited in size (typically 30 cm diameter). In this research, a new method is proposed that uses a temporary berm constructed of a water-filled 15-cm diameter vinyl hose with the edges sealed to the soil using bentonite. The berm is capable of confining infiltration plot areas of various sizes (e.g., $1\times 1$ and $3\times 3\mathrm{m}$ areas in this research). Water tanks with 0.8 and $4.9{\mathrm{m}}^3$ capacity were used to supply water to the plots by gravity flow. A constant head could be maintained within the plot using either an automatic float valve for lower infiltration rates or a manually operated gate valve for higher infiltration rates. Observation wells were installed outside the plots to monitor for water table rise and tracers that leached into the groundwater. Guidelines are provided for tank size and refilling frequency for conducting field experiments. The procedure was tested on soils ranging from silt loam to coarse gravel using 12 $1\times 1$ and $3\times 3\mathrm{m}$ plots at three alluvial floodplain sites. Measured infiltration rates ranged over two orders of magnitude ($0.8–74\mathrm{cm}/\mathrm{h}$) and were typically greater than the estimated permeability of the limiting layer reported in soil surveys, suggesting the need for larger scale field measurements of infiltration rates.