Berm method for quantification of infiltration and leaching at the plot scale in high conductivity soils

Measuring infiltration and leaching at the plot scale is difficult, especially for high hydraulic conductivity soils. Infiltration rate has been indirectly calculated at the plot scale by comparing surface runoff to rainfall. Direct measurement of infiltration and leaching beyond the point scale is typically limited to locations where land forming has been performed, e.g. infiltration ponds and fields with basin irrigation. The standard method for field measurement of infiltration is a 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 m by 1 m and 3 m by 3 m areas in this research). Water tanks (0.8 m³ and 4.9 m³) and gravity flow were used to supply water and tracers to the plots. A constant head was maintained within the plot automatically using float valves for lower flow rates and manually with a gate valve for higher flow rates. Observation wells were installed 0.5 m outside the plot to monitor for water table rise and tracers that leached into the groundwater. The procedure was tested on soils ranging from silt loam to coarse gravel with measured infiltration rates ranging from 5 to 70 cm/hr. Guidelines are provided for tank size and refilling frequency for field experiments. In addition, numerical simulations were performed to estimate time of response in wells for various soil and experimental design conditions.