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Water Flow through Intact Soil Columns: Measurement and Simulation Using LEACHM

Centre for Land and Biological Resources Research, Research Branch, Agriculture and Agri-Food Canada, Ottawa, ON, Canada. K1A 0C6.

^* Corresponding author.

ABSTRACT

An evaluation of the water flow submodel, LEACHW, of the LEACHM solute transport model was conducted using profiles of volumetric water content, (z), and hydraulic head, H(z), measured under steady sated and near-saturated flow conditions in two large, intact, soil columns. The hydraulic conductivity (K)-water content ()-pressure head () relationships, K--, required by LEACHW were obtained by fitting the Van Genuchten functions to measurements of sated hydraulic conductivity (K_s) and vs. obtained: (i) using in-situ TDR and tensiometer measurements, with the - data being collected during the initial column wetting; and (ii) using the traditional saturated flow-desorption technique on intact soil core subsamples collected from the columns at the end of the experiment. The LEACHW model provided reasonably accurate predictions of the (z) and H(z) profiles, regardless of whether the in-situ or soil core-based K-- relationships were used, and regardless of whether sated or near-saturated flow occurred. The LEACHW predictions were substantially more accurate, however, when the K-- relationships derived from the in-situ measurements were used. It was concluded that the LEACHW model, coupled with independently measured K-- functions, could provide reasonably accurate predictions of steady (z) and H(z) profiles in large, intact soil columns, regardless of whether the soil macropores are largely water-conducting (sated flow) or largely nonwater-conducting (near-saturated flow). It also appears that in-situ K_s and - measurements, with the - data collected during initial wetting, may provide more appropriate K-- relationships for use in water and solute transport models than the traditional saturated flow-desorption method using intact soil core subsamples.

CLBRR Contrib. No. 94-88.

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