SWRC Fit and unsatfit for parameter determination of unsaturated soil properties

TL;DR

This paper introduces SWRC Fit and unsatfit, tools for determining soil water retention and hydraulic conductivity parameters, facilitating analysis of water movement in unsaturated soils through user-friendly applications and advanced modeling techniques.

Contribution

The paper presents new software tools, SWRC Fit and unsatfit, that simplify parameter determination of soil hydraulic functions using nonlinear optimization and diverse soil models.

Findings

SWRC Fit enables easy plotting of soil water retention curves.

unsatfit implements multiple soil hydraulic models for parameter estimation.

The tools incorporate a modified hydraulic conductivity model to handle near-saturated conditions.

Abstract

SWRC Fit and unsatfit are programs developed for determining parameters of the water retention and the unsaturated hydraulic conductivity functions of soils for analyzing water movement in the unsaturated soil. The SWRC Fit is a web application for drawing SWRC (soil water retention curves) of various soil hydraulic models from the measured data with just one click, available at https://purl.org/net/swrc/. The SWRC Fit depends on the Python library unsatfit that implements various types of soil hydraulic models to determine water retention and hydraulic conductivity parameters by nonlinear least-square optimization. The implemented models are classified as DF3 (Brooks and Corey, van Genuchten, Kosugi) models, DF4 (Fredlund, Fayer, Peters, bimodal-CH) models, and DF5 (bimodal) models by the degree of freedom of the water retention functions. Most of the hydraulic conductivity functions are derived from the water retention function and the general hydraulic conductivity function. A modified model to suppress extreme changes in hydraulic conductivity in the near-saturated range can be applied to any hydraulic model. The algorithm that was proved to work with various types of soils in Seki et al. (2023) is provided as the sample Python codes. This paper describes how to use SWRC Fit and unsatfit.