Tile drain sampling of preferential flow on a field scale

Preferential flow phenomena generally exhibit a high degree of spatial variability. In an alternative to geostatistl approaches, which aggregate many small-scale sample results, tile drains were explored as a means to measure solute movement on a scale which integrates spatial variability within the sampling volume. To evaluate the effectiveness of this method, a mass balance accounting of a conservative tracer, chloride, was attempted over a seven-month period. Analysis of the drain effluent indicated rapid breakthrough of surface-applied chloride, with concentrations rising within four hours of rainfall initiation. This traveltime was over two orders of magnitude more rapid than that predicted by homogenous flow models, indicating the importance of preferential flow in the transport of solutes through this field. Close agreement between the amount of chloride initially applied and the cumulative chloride recovered by the end of the experiment indicates the ability of tile drains to intercept solute movement.