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Geoelectric Studies of Seasonal Wetting and Drying of a Texas Vertisol

Dep. of Geology, Baylor Univ., One Bear Place #97354, Waco, TX 76798-7354

View larger version (32K): [in this window] [in a new window]   FIG. 1. Study location: (a) location map of USDA Grassland Soil and Water Research Station, near Riesel, TX, showing the study site and distribution of monitoring wells within the station; and (b) sectional view of the experimental layout (MH = microhigh, ML = microlow, MI = intermediate microrelief). The electrodes are numbered 1 to 36.

View larger version (21K): [in this window] [in a new window]   FIG. 2. Examples of estimated temperature profiles in the Vertisol that were used for temperature corrections of the inverted resistivity data. The times indicated on the plot correspond to the average of the time span of resistivity surveys on each day.

View larger version (22K): [in this window] [in a new window]   FIG. 3. Experimental setup for the laboratory measurement of resistivity variations with soil moisture.

View larger version (18K): [in this window] [in a new window]   FIG. 4. Soil moisture–resistivity characteristics of the Texas Vertisol.

View larger version (23K): [in this window] [in a new window]   FIG. 5. Rainfall distribution during the period of study. The intervals corresponding to the wetting and drying cycles in the soil are indicated in the figure.

View larger version (28K): [in this window] [in a new window]   FIG. 6. Representative apparent soil moisture–inverted resistivity sections collected during Wetting Cycle 1 in the Vertisol: (a) 1 May; (b) 24 May; (c) 29 May; (d) 15 June; (e) 22 June; (f) 20 July; and (g) 16 Aug. 2005. The lateral extent of the microhighs (MH), microlows (ML), and the intermediate microrelief (MI) are shown in Fig. 6a. The areas marked "P" in (c) denote preferentially saturated portions of the soil in the section. The absolute error values refer to the errors in % from the robust inversion of the apparent resistivity data.

View larger version (25K): [in this window] [in a new window]   FIG. 7. Representative apparent soil moisture–inverted resistivity sections collected during the drying cycle in the Vertisol: (a) 27 August; (b) 9 September; (c) 17 September; (d) 8 October; (e) 28 October; (f) 30 November; and (g) 29 Dec. 2005. The absolute error values refer to the errors in % from the robust apparent resistivity data inversion.

View larger version (26K): [in this window] [in a new window]   FIG. 8. Representative apparent soil moisture–inverted resistivity sections collected during Wetting Cycle 2 in the Vertisol: (a) 24 January; (b) 4 February; (c) 26 February; (d) 1 March; (e) 23 March; and (f) 22 Apr. 2006. The absolute error values refer to the errors in % from the robust inversion of the apparent resistivity data.

View larger version (12K): [in this window] [in a new window]   FIG. 9. Comparisons of results of soil moisture values derived from resistivity measurements of 23 Mar. 2006 to those obtained from auger sampling on the same date: (a) measurements within the microhigh; (b) measurements within the microlow.