Infiltration rate assessment of some major soils

Abstract

An evaluation of the risk of overland flow is needed in order to minimise the risk of transferring pollutants from soil to rivers and lakes. The infiltration capacity of soil influences the occurrence of overland flow. The objectives of this study were to assess the infiltration capacity of some extensive soils in Ireland and also its spatial and temporal variability. Infiltration capacity was measured using double-ring infiltrometers at one poorly drained, one imperfectly drained and eight freely drained sites. The first series of measurements was performed for one day in summer. Eight years later a second series was performed for two days in winter and two days in summer at the same sites. On average, eight replicates were required in summer and fifteen in winter to estimate the mean with 50 percent precision. Infiltration capacities were reasonably stable between the two series but there was a significant difference between seasons. There was a significant relationship between infiltration capacity and the antecedent soil water content, which contributed to the seasonal effect. Capacities in summer were 3.5 times the winter values. In summer, the infiltration capacity exceeded or equalled the five-year return rainfall rate, except on the poorly drained soil, indicating that the risk of overland flow, due to infiltration excess, is negligible on well drained soils in summer. In winter, the infiltration capacity at nine of the ten sites, predominantly freely drained, was below the five-year return hourly rainfall indicating a risk of overland flow in winter.