The effect of ponding depth on infiltration in a crusted surface depression

Over the past few decades, the influence of surface sealing on infiltration has been the subject of numerous publications. However, very few of these experiments have considered the effect of spatial variability in seal hydraulic characteristics on infiltration. Field and laboratory observations have demonstrated that seal characteristics vary considerably within a range of a few cm, and the changes are often related to microtopography. The objective of this experiment was to investigate the influence on infiltration of a seal with varying hydraulic properties in a surface depression. Two soils of different aggregate stability were used in the experiment: Blosseville silt loam and Villamblain 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 intensity of 35 mm h(-1). Subsequently, water outflow at the base of the column and pressure heads in the column were measured during two pending periods corresponding to depths of 0.5 and 4.0 cm. Water outflow rates increased with pending depth substantially more than could be attributed 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 infiltration rate occurs as areas of greater hydraulic conductivity are submerged. The increases in ponded pressure head and submerged area are negligible compared to the influence of spatial variability in seal hydraulic conductivity. (C) 1998 Elsevier Science B.V. All rights reserved.