Detachment of soil particles by shallow flow: sampling methodology and observations

Although several scientists have recently studied overland flow detachment, the methodology of measurement has not yet been properly discussed. This study compares several different methods. A flume was constructed to measure soil detachment. Remoulded soils were tested in order to minimize the effects of sediment load and deposition on the soil sample surface by way of a suitable methodology. The soil sample sizes were established on the basis that erosion must scour the entire surface of the soil target. Incipient detachment rate, determined through the use of several methods, was compared with the condition for incipient entrainment and the method which showed the best agreement with Shields' criterion was selected. Two data sets collected following the selected procedure and a different one were compared. While the general trends deducible from the two data sets were similar, the difference in intensity of the detachment rate was close to a factor 10 showing that measurements of flow detachment rate are sensitive to the procedure applied. The sensitivity of the proposed methodology to various factors that can influence detachment was examined using remoulded and undisturbed soil samples. Particularly, differences in initial soil moisture conditions and soil surface characteristics due to the combined effects of various types of crops and applied raindrop kinetic energy caused differences in soil detachability by overland flow. Furthermore, soil sampling in different periods of the year resulted in variations in soil detachment indicating a seasonal trend in soil detachability.