Soil shear strength is inversely related to soil water matric potential (ψm), which changes in the soil during a rainstorm. An understanding of surface soil ψm changes due to rainfall may give an insight in soil erosion dynamics. Changes in soil water matric potential (ψm) under 1‐ and 3‐mm simulated soil surface seals were monitored following single waterdrop impacts on the soil surface. Selected ψm's were applied to the base of the seals with a hanging water column during the tests. After waterdrop impact, changes in ψm were detected within 2 to 3 s under 1‐mm surface seals and within 6 to 10 s under 3‐mm surface seals. The time required for ψm to equilibrate with the preimpact ψm (that ψm applied continuously with the hanging water column) ranged from 160 to 280 s. Equilibration time decreased slightly with increasing preimpact ψm's and was significantly affected by the type of soil material used to make the seal, the applied ψm, and the thickness of the seal. Increases in ψm under the 1‐mm surface seal due to waterdrop impact ranged from 0.3 to 0.5 kPa depending on ψm applied via the hanging water column. Smaller ψm changes were observed under the 3‐mm surface seal.
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Cruse et al. (1984) studied this question.