Disc permeameter fitting program
Project description
Discfit reads disc permeameter data in the field and calculates hydraulic parameters of the soil; saturated hydraulic conductivity and Gardner’s alpha constant.
Disc permeameter is a tool for measuring hydraulic properties in the field. Steady-state periods in multiple constant head period are selected automatically from the data, and infiltration rate for each steady-state period is calculated. After that, infiltration rate at saturated condition is estimated by Gardner’s exponential model,
K(h) = Ks exp(αh)
where K is unsaturated hydraulic conductivity (cm/s), h is matric head (cm), Ks is saturated hydraulic conductivity (cm/s), α is a constant (/cm). Note that h is negative and αh is negative. Based on this equation, the linear relationship ln(q) = ln(qs) + αh is used for estimating qs (cm/s), the infiltration rate at the saturated condition, and α constant, as we have multiple point of (h, q) data from the disc permeameter. The hydraulic conductivity is calculated from the infiltration rate based on steady-state analysis of Wooding (1968);
q = K(1 + 4 / παr)
where α is the Gardner’s α and r is the diameter of the disc (cm). See equations (10) and (13) in Minastry and George (1999).
Install
Python 2 or 3 is required. Install Python at https://www.python.org/ . After that, install discfit by running
pip install discfit
Usage
discfit Filename dd dp
where
Filename: File name of data file
dd: diameter of the disc (cm)
dp: inner diameter of the pipe (cm)
Format of data file
It is a csv file with time, water level, and suction head (absolute value of the matric head) as follows.
# Comment line starts with '#'
# Time (sec), Water level (cm), Suction head (cm)
0, 58.32, 10.53
10, 58.30, 10.57
20, 58.33, 10.48
Reference
Minasny, B., and B. H. George. 1999. The measurement of soil hydraulic properties in the field. in Cattle S.R. & George B.H. (Eds) Describing, Analysing and Managing Our Soil.
Wooding, R.A., 1968. Steady infiltration from a shallow circular pond. Water Resources Research 4, 1259-1273.
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