ABSTRACT
Luxmoore (1991) defines macropore flow as water movement through holes or channels that are 1 mm or more in width or diameter. In contrast, mesopore flow occurs in pores less than 1 mm in equivalent diameter. Micropores are those meso-pores capable of retaining water by surface tension at field capacity. Macropores have lower surface areas than mesopores, with little opportunity for affecting water quality during drainage. In contrast, mesopores have greater surface areas, affecting chemical reactions between the soil and pore liquids. Although the percentage of the total pore space occupied by macropores may be small (e.g., on the order of 0.5% to 5%), in many soils they may account for the bulk of the flow (Richard and Steenhuis, 1988). Water moving in macropores is generally termed “new water,” while water retained in micropores is called “old water” (Luxmoore, 1991). During studies in a steep humid catchment in New Zealand, McDonnell (1990) determined that macropore flow contained both “old water” as well as “new water”. Additional aspects of macroscopic flow as a factor in preferential flow are reviewed by Steenhuis and Parlange (1991).
