FRACTAL MODELS FOR PREDICTING SOIL HYDRAULIC-PROPERTIES - A REVIEW

Modern hydrological models require information on hydraulic conductivi ty and soil-water retention characteristics. The high cost and large s patial variability of measurements makes the prediction of these prope rties a viable alternative. Fractal models describe hierarchical syste ms and are suitable to model soil structure and soil hydraulic propert ies. Deterministic fractals are often used to model porous media in wh ich scaling of mass, pore space, pore surface and the size-distributio n of fragments are all characterized by a single fractal dimension. Ex perimental evidence shows fractal scaling of these properties between upper and lower limits of scale, but typically there is no coincidence in the values of the fractal dimensions characterizing different prop erties. This poses a problem in the evaluation of the contrasting appr oaches used to model soil-water retention and hydraulic conductivity. Fractal models of the soil-water retention curve that use a single fra ctal dimension often deviate from measurements at saturation and at dr yness. More accurate models should consider scaling domains each chara cterized by a fractal dimension with different morphological interpret ations. Models of unsaturated hydraulic conductivity incorporate fract al dimensions characterizing scaling of different properties including parameters representing connectivity. Further research is needed to c larify the morphological properties influencing the different scaling domains in the soil-water retention curve and unsaturated hydraulic co nductivity. Methods to functionally characterize a porous medium using fractal approaches are likely to improve: the predictability of soil hydraulic properties. (C) 1997 Elsevier Science B.V.