THE EFFECT OF PONDING DEPTH ON INFILTRATION IN A CRUSTED SURFACE DEPRESSION

Over the past few decades, the influence of surface sealing on infiltr ation has been the subject of numerous publications. However, very few of these experiments have considered the effect of spatial variabilit y in seal hydraulic characteristics on infiltration. Field and laborat ory observations have demonstrated that seal characteristics vary cons iderably within a range of a few cm, and the changes are often related to microtopography. The objective of this experiment was to investiga te the influence on infiltration of a seal with varying hydraulic prop erties in a surface depression. Two soils of different aggregate stabi lity were used in the experiment: Blosseville silt loam and Villamblai n silty clay loam. Soil columns (23 cm diameter by 30 cm length) were packed with aggregates of < 2.0 cm and a 6 cm depression was formed in the soil surface. A sedimentary crust was formed in the centre of the depression, and the sample was rained upon for 60 min at a rainfall i ntensity of 35 mm h(-1). Subsequently, water outflow at the base of th e column and pressure heads in the column were measured during two pen ding periods corresponding to depths of 0.5 and 4.0 cm. Water outflow rates increased with pending depth substantially more than could be at tributed to the increases in ponding pressure head and submerged area for both soils. The experiment demonstrated that where seal hydraulic conductivity varies with microtopography, a significant increase in in filtration rate occurs as areas of greater hydraulic conductivity are submerged. The increases in ponded pressure head and submerged area ar e negligible compared to the influence of spatial variability in seal hydraulic conductivity. (C) 1998 Elsevier Science B.V. All rights rese rved.