The borehole infiltrometer, also called borehole permeameter, is designed to determine the saturated hydraulic conductivity of soil at various depths below ground surface, but above the water table.
The permeameter method requires a 10 cm (4 inch) outside diameter borehole to the depth of interest using a hand auger or a standard drill rig. After filling the permeameter with water, it is lowered in the borehole till it hits the bottom. When ready for measurements, the bottom valve of the permeameter is opened causing water to flow into the borehole. After a very short time the water level in the borehole reaches a preset level (i.e. 15 cm or more above the bottom), at which time the out-flow rate from the permeameter (the volume of water entering the soil around the borehole) decreases, and over time approaches a constant value.
Once the outflow rate from the permeameter has reached a constant value, the volume of water entering the soil around the borehole is determined from the known inside crosssectional area of the permeameter, and the decrease in water level inside the permeameter with time. The water level inside the permeameter is measured at ground surface with a handheld, digital manometer connected with plastic tubing to the top of the permeameter inside the borehole. It can also be measured with a pressure transducer connected with plastic tubing to the top of the permeameter. Connecting the pressure transducer to a datalogger allows for automated measurement of the hydraulic conductivity.
Inside diameter of permeameter 7.0 cm (2.75")
Outside diameter of permeameter 7.6 cm (3.0")
Length of permeameter 82 cm
Effective storage volume inside permeameter 2500 ml
After each experiment, the water level with time data is down loaded to an excel spreadsheet which is used to compute the outflow rate. Next the outflow rate is plotted versus time. The slope of the outflow rate versus time relationship is determined at the point where the outflow rate has reached a nearly constant value. The slope value is then entered in the equation to calculate the saturated hydraulic conductivity. All of this can be done in a short spreadsheet program.
The excel spreadsheet program with all calculations is provided with the instrument.
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