Preferential flow in a sandy vadose zone: 1. Field observation

Abstract

Field experiments of water movement in the lower portion of an unsaturated zone (i.e., vadose zone) are far more difficult to conduct than those in the root zone; thus our concept of the transport mechanism in the vadose zone is still primitive and mainly an extrapolation of our understanding of transport in the root zone. Recent results from field experiments conducted at the Hancock Agricultural Research Station indicated that water and solute applied uniformly to soil surfaces did not flow through the entire vadose zone. By using dye tracing and profile excavation, field experiments were conducted during the 1987 growing season to examine water flow patterns in the unsaturated zone of the Central Sand Area of Wisconsin (CSAW). The results confirmed that preferential flow paths constitute the dominant flow pattern at this location. Water flowing through the root zone was funneled into concentrated flow paths that occupied only a small portion of the soil matrix in the vadose zone yet accounted for most of the transport. The observed phenomena of preferential flow in a sandy vadose zone are discussed in this paper. The mechanism and implications of preferential flow are presented in a companion paper.