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Field measurement of time to ponding

Abstract. Field measurements of cumulative infiltration and of the matric potential prior to infiltration were made with double‐ring infiltrometers and tensiometers, respectively, on two sandy loams in north‐east Scotland. The time to ponding for constant‐rate infiltration was also measured in the same infiltrometers by applying water at a constant rate until ponding commenced. Under the range of initial potentials studied (‐2 to ‐ 17 kPa), an exponential relation was adequate to describe the relation between sorptivity and initial matric potential. The time to ponding was also strongly dependent on initial matric potential and increased dramatically as the soil became drier. Measurements of time to ponding were in good agreement with values predicted from the theory of Clothier et al. (1981) using values for sorptivity and the A parameter obtained from the cumulative infiltration experiments. Measurements and predictions clearly showed the importance of the sorptivity versus initial matric potential relation in controlling the time to ponding of such sandy soils. These results have implications for determining the generation of runoff and the establishment of stream flows, as well as determining optimum rates and design of irrigation.