Three-dimensional Fingered Flow Patterns in a Water Repellent Sandy Field Soil

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Abstract
Water flow and transport through the vadose zone of water repellent field soils take place mainly through preferred flow paths. For modeling purposes, it is essential to know when fingers can be expected and what is their average dimension. Therefore, 10 soil blocks, each 1.2 m long, 0.6 m wide, and 0.52 m deep, were sampled in a water repellent sandy field soil. Sampling took place according to a predefined spatial grid, whereby 200 (100-cm3) cylinders were sampled at seven depths yielding a total of 1400 samples per soil block. Each sample was used for the determination of soil water content, and some of the samples were used for the determination of the degree of potential water repellency. Three-dimensional water content patterns and water repellency distributions were visualized. Fingered flow patterns were distinct in soil blocks sampled after rain events. Fingers were found at places where the degree of potential water repellency in the upper part of the soil was low. Soil blocks sampled between rain events showed only remnants of fingerlike wetting patterns as result of continuing processes like drainage, redistribution, and evaporation. Water contents were less heterogeneously distributed in these soil blocks, as was the case as well for a very wet soil block sampled after an abundant amount of rainfall.