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Sand Detachment by Single Raindrops of Varying Kinetic Energy and Momentum

LRRC, North Dakota State Univ., P.O. Box 459, Mandan, ND 58554

S. C. Gupta

Dep. of Soil Science, Univ. of Minnesota, St. Paul, MN 55108

*Corresponding author.

ABSTRACT

Soil detachment by raindrops is a precursor to the start of interrill erosion and surface seal formation. Soil detachment occurs when erosive forces of raindrops are greater than the inherent strength of soil. Experiments were conducted to study the importance of inherent soil strength on detachment of soil by raindrops. Sand strength was controlled by varying matric potentials before raindrop impact. A range of raindrop kinetic energies and momentum was created by changing drop diameter (3.6–5.0 mm) and fall height (1–8 m). The experimental setup consisted of a varying height water drop former, an electronic drop discriminator, and a single-drop soil splash collector. Splash collected by varying drop height of a 4.6-mm-diam. drop on sand equilibrated at a matric potential (_m) of –1.5 kPa (higher strength) showed that a larger threshold energy is needed to initiate soil detachment than when equilibrated at _m = –0.1 kPa (lower strength). Also, the threshold erosivity was larger in magnitude and more significant when using momentum as an index of erosivity instead of kinetic energy. The relationships between sand splash and erosivity were linear (P < 0.001) for raindrops with diameters of 3.6 to 5 mm falling from heights of 0.76 to 7.6 m on sand equilibrated at _m = –1.0 kPa. Sand splash was represented by a model of the form D = K_d[E – E_o]^b, where D is detachment, E is raindrop erosivity, E_o is threshold erosivity, K_d is sand detachability, and b is an exponent equal to 1. This equation of describing soil detachment as a function of erosivity is an improvement over the currently used nonlinear relationship of the form D = K_d E^b.

Contribution from the Minnesota Agric. Exp. Stn., Dep. of Soil Science, Univ. of Minnesota, Scientific Journal Series, Paper No. 16167.

Received for publication July 22, 1988.

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