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Four infiltration models for disc tension permeameters were compared to field and simulated data. Comparisons were made in order to assess the alternative values of sorptivity and steady state flow rates. Model 1 was the conventional analysis with assumptions of one-dimensional flow at small times and Wooding's steady state flow rate at large times. Model 2 was a modified Horton equation defined to fit one-dimensional infiltration at small times with an exponential decay to a steady state value for large times. Model 3 assumed linear diffusion for a soil with constant diffusivity ignoring gravity. Model 4 was based on "linearized" flow with gravity. The number of unknown parameters to be estimated ranged from one to four. Sorptivity data using models 2 and 3 generally agreed with the conventional method (model I) both for the field and simulated data. For the steady state infiltration rate, all of the models gave generally consistent results. Model 2 with four parameters was the best fitting model to field and simulated data. The simulated data allowed comparisons of results based on the total time over which the parameters were evaluated. Results were sensitive to the time of evaluation up to 0.3-1.3 hours for the sandy loam soil. HUSSEN AND WARRICK: ALGEBRAIC MODELS FOR Disc TENSION PERMEAMETERS Weir, G. J., Steady infiltration from small shallow circular ponds, Water Resour. Res., 23,733-736, 1987. White, i., and M. J. Sully, Macroscopic and microscopic capillary length and time scales from field infiltration, Water Resour. Res., 23, 1514-1522, 1987. White, I., and M. •[. Sully, Field characteristics of the macroscopic capillary lengths or alpha parameter, in International Conference and Workshop on the Validation of Flow and Transport Models for the Unsaturated Zone, edited by P. J. Wierenga and D. Bachelet, pp. 517-524, New Mexico State University, Las Cruces, 1988. Wooding, R. A., Steady infiltration from a shallow circular pond, Water Resour. Res ., 4, 1259-1273, 1968. Yitayew, M., and J. E. Watson, Field methods for determining unsaturated hydraulic conductivity, Pap. Am. Soc. Agric. Eng.,

Abstract--The occurrence of palygorskite in some Tertiary sediments in eastern Saudi Arabia was studied. Mineralogical and chemical analyses were made of samples from two sections several meters thick from the Umm er Radhuma and Dammam Formations of Paleocene and Eocene periods, respectively. Layers of shales were observed within the sections of the dolomitic-calcitic limestone of the Umm er Radhuma Formation and of the dolomitic limestone of the Dammam Formation. After treatment for carbonate removal the shales consisted of more than 95% clay-size particles, most of which were <0.2-#m in size. Palygorskite was the main constituent of some of the shales, with minor amounts of gypsum, soluble salts, and carbonates. The association of gypsum and other salts with palygorskite in the shale suggests that palygorskite formed in closed-basin environments. The presence of palygorskite and the absence of other minerals in the clay fraction of the limestones also suggests that the palygorskite formed under marine conditions.

Hydraulic conductivity values were compared based on alternative analyses of data from disc tension infiltrometers. The first method was based on a single disc and tension and depends on the estimate of sorptivity and steady state flow. A second method used steady state flow measurements for two different disc radii, 52 and 118 mm. A third method used a single disc with multiple tensions from which steady state flow was obtained at three or more tensions which could be at the same location. A fourth method used a single disc with two tensions from which steady state flow was obtained at two tensions. Finally, values based on soil cores were compared. The results show reasonable agreement between methods for the hydraulic conductivity with the largest differences for data collected for zero tension. For the most part, there were no significant differences in hydraulic conductivity due to the disc infiltrometer radius. A single-disc method with multiple tensions (more than 3 points) and large disc radius gave results which were the most stable, accurate, and repeatable. Wooding, R. A., Steady infiltration from a shallow circular pond, Water Resour. Res., 4, 1259-1273, 1968. Yitayew, M., and J. E. Watson, Field methods for determining unsaturated hydraulic conductivity, Pap. 86-2570, Am. Soc. Agric. Eng., St. Joseph, Mich., 1986.

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