  Many soils and other porous media exhibit dual- or multi-porosity type
features. In a previous study (Seki et al., 2022) we presented multimodal water
retention and closed-form hydraulic conductivity equations for such media. The
objective of this study is to show that the proposed equations are practically
useful. Specifically, dual-BC (Brooks and Corey)-CH (common head) (DBC),
dual-VG (van Genuchten)-CH (DVC), and KO (Kosugi)$_1$BC$_2$-CH (KBC) models
were evaluated for a broad range of soil types. The three models showed good
agreement with measured water retention and hydraulic conductivity data over a
wide range of pressure heads. Results were obtained by first optimizing water
retention parameters and then optimizing the saturated hydraulic conductivity
(K_s) and two parameters (p, q) or (p, r) in the general hydraulic conductivity
equation. Although conventionally the tortuosity factor p is optimized and (q,
r) fixed, sensitivity analyses showed that optimization of two parameters (p+r,
qr) is required for the multimodal models. For 20 soils from the UNSODA
database, the average $R^2$ for log (hydraulic conductivity) was highest
(0.985) for the KBC model with r=1 and optimization of (Ks, p, q). This result
was almost equivalent (0.973) to the DVC model with q=1 and optimization of
(Ks, p, r); both were higher than $R^2$ for the widely used Peters model
(0.956) when optimizing (Ks, p, a, $\omega$). The proposed equations are useful
for practical applications while mathematically being simple and consistent.
