In Situ Measurement of Preferential Flow

An experiment was performed that quantifies the variability of flow paths in the vadoze zone. Bromide tracer and an organic dye, which has many of the same transport characteristics as pesticides, were applied at a slow rate on the land surface and then collected using pan lysimeters. The bromide and dye breakthrough curves were analyzed and inferences were made of the flow paths. The experiment was performed at two sites, one in Delaware in well-drained loamy sand soil, the other in New York in somewhat poorly drained sandy loam soil. The findings indicate the existence of preferential flow by two different mechanisms at the two different sites. In the coastal loamy sand soil, flow occurred through fingers in an unstable flow field. In the glacial till soil, macropore flow was evident.