Rainwash experiments on the erodibility of loose sediments

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Abstract
Laboratory experiments using simulated rainfall, splash boards and trays were conducted in order to obtain information on the erodibility of loose sediments as a time‐dependent phenomenon. In all, ten different sediments ranging from silt (D50= 24μm) to coarse sand (D50= 593 μm) were studied. The effect of three different initial states of the sediments, namely the air dry state T1, the field capacity state T2, and the desiccated state T3, on the erodibility was also assessed.Variations in detachability during a rain erosion experiment can be explained by change in water content (including liquefaction and the development of a water layer on the surface), cohesion, and granulometric composition of the top layer. The coarsest sandy sediments almost always yielded the highest detachability when starting from an initial field capacity state, T2. For the finer sediments, the highest detachability was found for the homogeneous and not yet compacted initial air dry state, T1. The effect of the initial desiccated state T3 on the detachability of the finer sediments was also a function of the rainfall duration.The relationship between detachability and median grain size of the sediments was very similar to the relation between grain size and the susceptibility to runoff and wind erosion established by other investigators. The highest detachability was found for a fine very well sorted sand with a median grain size of 96 μm.