Single Raindrop Research Articles

A model of the redistribution of disaggregated soil particles by rainsplash

AbstractA model of the dispersion of splash droplets from a single raindrop impact on a sloping soil surface is combined with a theory of the entrainment of mineral particles from a disaggregated mixture in splash droplets to obtain a model of the dispersion of such particles by a raindrop impact. Stochastic modelling techniques extend this further to a model of the spatial redistribution of soil on a plot after a period of rainfall.Since the model is probabilistic and physically based it enables the incorporation of further advances in the understanding of splash erosion at all stages and can simulate the effect of the stochastic nature of rainfall and soil properties on the process. Several different situations are simulated. These include the movement of marked soil particles from point sources and the spatial patterns of erosion on a sloping plot. The model can also simulate the differential erosion of different soil particle size fractions.

Collision, Coalescence and Breakup of Raindrops. Part I: Experimentally Established Coalescence Efficiencies and Fragment Size Distributions in Breakup

Abstract The collision, coalescence and breakup of single raindrop pairs were studied at terminal velocities and laboratory pressure (100 kPa) in 761 collision experiments (out of 14 000 attempts). Six size combinations were used with drop pair diameters of [0.18;.0.0395 cm], [0.40; 0.0395 cm], [0.44; 0.0395 cm], [0.18; 0.0715 cm], [0.18; 0.10 cm] and [0.30; 0.10 cm]. For averaging purposes the experiments were repeated over one hundred times for each pair. The new coalescence efficiencies and fragment size distributions in breakup turned out to be consistent with those of McTaggart-Cowan and List (1975b) and permitted the combination of the two data sets into a single data bank spanning essentially the entire range of raindrop sizes. The analysis addressed three main geometric shapes formed by the drops after initial contact, namely, filaments, sheets and disks, and the fragment size distributions after breakup. Significant collisional growth, i.e., coalescence, occurred only when drops <0.06 cm in diame...

Parameters for Describing Soil Detachment Due to Single Waterdrop Impact

AbstractA simple relationship that predicts soil detachment due to single raindrop impact was tested for nine soils and three drop sizes. This relationship expressed splash weight as a linear function of the ratio of raindrop kinetic energy to soil resistance expressed as the undrained shear strength. The coefficient of determination values between splash weight and the force‐resistance ratio for individual soils were high (r2 = 0.88 to 0.97); however, the coefficient of determination among all soils was lower (r2 = 0.81). This was due to differences among soils in the slope of the regression line and to uncertainties associated with the calibration of the fall‐cone penetration apparatus. The slope was highly correlated with percent clay, organic matter, surface area, exchangeable sodium, and the amount of soluble salts. A maximum coefficient of determination of 0.61 was found when soil properties other than shear strength were used as independent variables to predict soil splash.

Physics of a raindrop

The author considers the basic physics governing the growth of a single raindrop by condensation and droplet capture, leading to such properties as falling speed, shape, and stability.