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Soil Water Retention

I. Introduction of a Shape Index

^a Laboratoire d'Etude des Transferts en Hydrologie et Environnement, LTHE (UMR 5564, CNRS, INPG, UJF, IRD), BP 53X, 38041, Grenoble, Cedex 9, France
^b Instituto Mexicano de Tecnología del Agua (IMTA), Paseo Cuauhnáhuac 8532, Col. Progresso 62550 Jiutepec, Morelos, Mexico
^c Dep. of Civil Engineering, California State Univ., Long Beach, CA 90840, USA
^d CSIRO Land and Water, Indooroopilly, Qld. 4067, Australia

View larger version (22K): [in a new window]   Fig. 1. Textural distribution of databases: (a) 406 samples from UNSODA and (b) 660 samples from GRIZZLY.

View larger version (46K): [in a new window]   Fig. 2. Histogram of dry bulk density, b, and organic matter content, OM, for 660 samples from GRIZZLY.

View larger version (32K): [in a new window]   Fig. 3. Histogram of the vG-shape factor mn0,2 optimized for 660 samples from GRIZZLY.

View larger version (48K): [in a new window]   Fig. 4. Saturated water content obtained from different parameterizations for 660 samples from GRIZZLY as a function of s for the van Genuchten (vG) equation with the Burdine condition (k = 2) and r = 0: (a) s for the Brooks-Corey (BC) equation (k) with r = 0, (b) s for the vG equation with the Mualem condition (k = 1) with r = 0, and (c) s for the vG equation with the Burdine condition (k = 2) with r > 0.

View larger version (14K): [in a new window]   Fig. 5. The shape factor mn with r optimized as a function of mn0,2 with r = 0 for the van Genuchten equation for 253 samples from GRIZZLY subject to the Burdine condition (k = 2).

View larger version (15K): [in a new window]   Fig. 6. The van Genuchten shape factor mn0,k for three different user indices, k, as a function of the Brooks-Corey shape parameter 0 for 660 samples from GRIZZLY.

View larger version (19K): [in a new window]   Fig. 7. The behavior of optimized hydraulic parameters for GRIZZLY as a function of the user index for the van Genuchten equation with k representing the Brooks-Corey equation: (a) values for s, hvG or hBC and mn0,k or 0 divided by their maximum obtained for either r = 0 or r > 0 as a function of k (error bars denote 95% confidence limits) and (b) adjusted RMSE as a function of k with r fixed (=0) or optimized (0).

View larger version (27K): [in a new window]   Fig. 8. Distribution of shape index, P, calculated for 461 soil samples from UNSODA and 612 samples from GRIZZLY.

View larger version (15K): [in a new window]   Fig. 9. Shape index computed from retention data as a function of clay and sand percentage plotted for 51 data points for: (a) UNSODA, and (b) GRIZZLY.