Mini-Disk Infiltrometer

Decagon's handheld Mini-disk Infiltrometer measures soil hydraulic conductivity quickly and easily in any soil type. The infiltrometer is constructed of a polycarbonate tube with a semi-permeable stainless steel sintered disk on the bottom. An adjustable steel tube above the sample chamber regulates the discharge rate.

Decagon's infiltrometers are ideal for soil hydrology studies, classroom instruction, and many other applications that rely on accurate measurement of hydraulic conductivity.

How it works:
The top and bottom chambers are both filled with water. The top chamber controls the infiltrometer's suction. The lower chamber contains the water that will infiltrate into the soil and is marked like a graduated cylinder. Place the full infiltrometer on the soil and record the water level (every 30 seconds for a silt loam soil). To calculate hydraulic conductivity input the water levels, soil type (according to the Van Genutchen parameters), and the suction you chose into the provided spreadsheet.

Below is the mathematical explanation. You can download the Excel spreadsheet to
perform the calculations from the download section of the website. This spreadsheet
will calculate the slope of the curve of the cumulative infiltration vs. the square root
of time based on the data gathered.
Infiltrometer Excel Spreadsheet

Theory:
The resulting measurements of infiltration vs. time are fitted with the function:

I = (C₁t + C₂√t)

The hydraulic conductivity is then calculated from:

k = C₁ / A

A is computed from:

A = (11.65(n^0.1 - 1) exp[2.92(n - 1.9)αh₀]) / (αr₀)^0.91
for (n ≥ 1.9)

or

A = (11.65(n^0.1 - 1) exp[7.5(n - 1.9)αh₀]) / (αr₀)^0.91
for (n < 1.9)

where n and a are the van Genuchten parameters for the soil, r_o is the disk radius, and h_o is the suction at the disk surface.