A spatial analysis of lateral and vertical fluxes of water associated with a perched watertable in a duplex soil

Abstract

Rates of lateral and vertical movement of water were investigated when severe waterlogging occurred as a result of a perched watertable over a clay subsoil in a duplex soil on a low (1.6%) slope in Western Australia. The severity of waterlogging and both the lateral and vertical fluxes of water at the 1.4 ha site were very spatially variable. Lateral water movement occurred in response to topographical gradients in the soil surface and the depth of the clay layer. As a result of this lateral redistribution of water, the depth of the watertable was greater in some areas, causing higher rates of vertical water loss (1.6–1.7 mm/day) compared with the rest of the site (1.2–1.5 mm/day).

Net gains or losses in water in experimental plots at the site due to lateral flow were 1–2 orders of magnitude smaller than vertical losses. Net lateral losses were less than 0.3 mm/day, but vertical losses ranged from 1.2 to 1.7 mm/day. We conclude that vertical drainage beneath crops growing on a duplex soil with a heavy clay subsoil can be significant when a head of water develops under climatic conditions conducive to waterlogging. In contrast, net lateral movement was generally small because of the low slope at the site (gradient of 0.016), and is likely to be insignificant at this site and other sites with duplex soils on similarly low slopes.