Spatially variable soil hydraulic properties for simulation of field-scalesolute transport in the unsaturated zone

Spatial variability of the soil hydraulic properties affects unsaturated fi eld-scale solute transport. We obtained the hydraulic properties of a sandy loam and a loam soil through pressure outflow experiments and assessed the ir variability by a scaling procedure. We used the soil hydraulic propertie s to quantify solute transport in a fallow field over a 214-day period as a function of water table depth with the one-dimensional, vertical, transien t SWAP93 model. For the sandy loam soil, simulated cumulative soil evaporat ion and cumulative bottom flux showed large spatial variability (standard d eviation of 100 to 150 mm). For the loam soil, this variability was limited (standard deviation of 4 to 16 mm). Scaled mean soil hydraulic properties could describe the water balance and depth-wise soil salinity of the loam s oil accurately. Scaled mean soil hydraulic properties did not perform satis factory for the sandy loam soil. Use of mean soil hydraulic properties with a field-scale dispersivity value (often done in model applications) yielde d deviating results for both soils, and is not recommended. Solute transpor t for both soils proved insensitive to spatial variability of the porosity. (C) 1999 Elsevier Science B.V. All rights reserved.