Hydraulic parameters define the water retention, θ(ψ), and the unsaturated hydraulic conductivity, K(θ), functions. These functions are usually obtained by fitting experimental data using inverse modelling. The drawback of inverting the hydraulic parameters is that they suffer from non-uniqueness and the optimal hydraulic parameters may not be physical. To reduce the non-uniqueness, it is necessary to invert the hydraulic parameters simultaneously from observations of θ(ψ) and K(θ), and ensure the measurements cover the full range of θ from saturated to oven dry. The challenge of using bimodal θ(ψ) and K(θ) compared to unimodal functions is that it requires double the number of parameters, one set for the matrix and another set for the macropore domain. The objective of this paper is to address this shortcoming by deriving a procedure to reduce the number of parameters to be optimized to obtain a unique physical set of bimodal soil Kosugi hydraulic parameters from inverse modelling. To achieve this, we (1) derive residual volumetric soil water content from the Kosugi standard deviation parameter of the soil matrix, (2) derive macropore hydraulic parameters from the water pressure head threshold between macropore and matrix flow, and (3) dynamically constrain the Kosugi hydraulic parameters of the soil matrix. The procedure successfully reduces the number of optimized hydraulic parameters and dynamically constrains the hydraulic parameters without compromising the fit of the θ(ψ) and K(θ) functions, and the derived hydraulic parameters are more physical. The robustness of the methodology is demonstrated by deriving the hydraulic parameters exclusively from θ(ψ) and K_s data, enabling satisfactory prediction of K(θ) even when no additional K(θ) data are available.

水力参数定义了保水率θ ( ψ ) 和不饱和导水率K ( θ ) 函数。这些函数通常是通过使用逆建模拟合实验数据来获得的。反演水力参数的缺点是它们具有非唯一性，并且最佳水力参数可能不是物理的。为减少非唯一性，需要对θ ( ψ ) 和K ( θ ) 的观测值同时反演水力参数，并确保测量值覆盖θ的全范围从饱和到烘干。使用双峰θ ( ψ ) 和K ( θ) 与单峰函数相比，它需要两倍数量的参数，一组用于矩阵，另一组用于大孔域。本文的目的是通过推导减少要优化的参数数量的程序来解决这一缺点，以便从逆向建模中获得一组独特的双峰土壤 Kosugi 水力参数。为此，我们 (1) 从土壤基质的 Kosugi 标准偏差参数中推导出剩余体积土壤含水量，(2) 从大孔隙和基质流动之间的水压头阈值中推导出大孔隙水力参数，以及 (3) 动态约束土壤基质的 Kosugi 水力参数。θ ( ψ ) 和K ( θ ) 函数，导出的水力参数更具物理性。该方法的稳健性通过完全从θ ( ψ ) 和K _s数据导出水力参数来证明，即使没有额外的K ( θ ) 数据可用，也能对K ( θ ) 进行令人满意的预测。