Identifying longitudinal and transverse dispersion of solutes in unsaturated porous media using dye tracer, image processing and spatial moment approach

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  • 色素トレーサと画像処理，空間モーメント法を融合した不飽和領域における縦分散と横分散の推定

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A new methodology using spatial moment analysis linked with image processing of a dye tracer behavior in porous media was developed to estimate dispersivities not only in longitudinal but in transverse directions. Laboratory tracer experiments using a relatively mobile dye tracer Brilliant Blue FCF were conducted under saturated and unsaturated flow conditions. Uniformly packed homogeneous fields, which were comprised by silica sand or andisol taken from a maize field, were of concern under four different infiltration rates as well as under saturated flow conditions. An image processing technique based on digitalized spatial distributions of dye tracer allowed to link with a spatial moment approach to identify the transverse and longitudinal dispersivities. Dispersivities exhibited an increasing and decreasing tendency associated with infiltration rates and showed a marked difference between estimates under saturated and unsaturated conditions. Laboratory study was extended by a comprehensive literature search to compare the new results with earlier work, demonstrating a good agreement between the experimental and published results. Developed methodology was applied to a field with approximately 100 cm depth from the ground surface under unsaturated conditions. Dye tracer moved through the soils in a preferential path pattern, which induced higher dispersivities in more irregular pore patterns as compared with estimates obtained in laboratory tracer experiments. Experimental results demonstrated the effectiveness of the developed methodology for simultaneous assessment of transverse and longitudinal dispersion in unsaturated soils.

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