Algebraic models for disc tension permeameters

Abstract

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.,

Steady state lateral water flow through unsaturated soil layers

“…[39] We now examine the effect of the slope, g, on flow through a homogeneous bed, driven only by gravity (h 1 = h 2 ). A plot of the flow through a sloped layer compared to the flow through the same layer oriented vertically is given as a function of the slope angle in sandy loam [Hussen and Warrick, 1993] for d = 0.1 m and d = 0.25 m. For the thinner slab of fine sand ( Figure 4A) the flow ratios start from 0 and advance monotonically toward 1 as the slope ranges from 0 to 90 degrees for all values of H 1 , as expected. Results are similar for the thicker slab of fine sand ( Figure 4B), but the rate of increase is small for small slopes and then increases as the slope approaches 90 degrees.…”

Improving Infiltration of Irrigated Mediterranean Soils with Polyacrylamide

“…Several methods have been developed to evaluate the hydraulic properties of the soil porous media. Recently, the disc in"ltrometer has become a popular device for determining in situ soil hydraulic properties such as the saturated and unsaturated hydraulic conductivity, sorptivity and the macropore capillary length (White & Sully, 1987;Smettem & Clothier, 1989;White et al, 1992;Hussen & Warrick, 1993. Disc in"ltrometer measures steady-state in"ltration rates una!ected by changing water potential gradients within soil pro"le.…”

Alternative analyses of hydraulic data from disc tension infiltrometers

“…Because of the sensitivity of soil hydraulic properties to soil structure, in situ methods are, potentially at least, more accurate. Recently, the disc infiltrometer has become a popular device for determining in situ hydraulic properties of soil [White and Sully, 1987;Ankeny et al, 1988' Smettem andClothier, 1989;Hussen, 1991;White et al, 1992;Hussen and Warrick, 1993]. They are designed to measure intake at a carefully controlled water pressure within a circular interface at the soil surface.…”