Rainfall characteristics such as total amount and rainfall intensity (I) are important inputs in calculating the kinetic energy (KE) of rainfall. Although KE is a crucial indicator of the raindrop potential to disrupt soil aggregates, it is not a routinely measured meteorological parameter. Therefore, KE is derived from easily accessible variables, such as I, in empirical laws. The present study examines whether the equations which had been derived to calculate KE of natural rainfall are suitable for the calculation of KE of simulated rainfall. During the experiment presented in this paper, the measurement of rainfall characteristics was carried out under laboratory conditions using a rainfall simulator. In total, 90 measurements were performed and evaluated to describe the rainfall intensity, drop size distribution and velocity of rain drops using the Thies laser disdrometer. The duration of each measurement of rainfall event was 5 minutes. Drop size and fall velocity were used to calculate KE and to derive a new equation of time-specific kinetic energy (KE_time – I). When comparing the newly derived equation for KE of simulated rainfall with the six most commonly used equations for KE_time – I of natural rainfall, KE of simulated rainfall was discovered to be underestimated. The higher the rainfall intensity, the higher the rate of underestimation. KE of natural rainfall derived from theoretical equations exceeded KE of simulated rainfall by 53–83% for I = 30 mm/h and by 119–275% for I = 60 mm/h. The underestimation of KE of simulated rainfall is probably caused by smaller drops formed by the rainfall simulator at higher intensities (94% of all drops were smaller than 1 mm), which is not typical of natural rainfall.

Abstract. Vegetation cover is found to be an ideal solution to most problems of erosion on steep slopes. Biodegradable geotextiles (GTXs) have been proved to provide sufficient protection against soil loss in the period before vegetation reaches maturity, so favouring soil formation processes. In this study, 500 g m −2 jute (J500), 400 g m −2 (C400), and 700 g m −2 coir (C700) GTXs were first installed on a 9 • slope under "no-infiltration" laboratory conditions, then on a 27 • slope under natural field conditions. The impact of GTXs on run-off and soil loss was investigated to compare the performance of GTXs under different conditions. Laboratory run-off ratio (percentage portion of control plot) equalled 78, 83, and 91 %, while peak discharge ratio equalled 83, 91, and 97 % for J500, C700, and C400 respectively. In the field, a run-off ratio of 31, 62, and 79 %, and peak discharge ratio of 37, 74, and 87 % were recorded for C700, J500, and C400 respectively. All tested GTXs significantly decreased soil erosion. The greatest soil loss reduction in the field was observed for J500 (by 99.4 %), followed by C700 (by 97.9 %) and C400 (by 93.8 %). Irrespective of slope gradient or experimental condition, C400 performed with lower run-off and peak discharge reduction than J500 and C700. The performance ranking of J500 and C700 in the laboratory differed from the field, which may be explained by different slope gradients, and also by the role of soil, which was not included in the laboratory experiment.

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Abstract. A vegetation cover is found to be an ideal solution to most problems with erosion on steep slopes. Biodegradable geotextiles (GTX) have been proved to provide a sufficient protection against soil loss in the period before the vegetation reaches maturity. In this study, 500 g.m−2 jute (J500), 400 g.m−2 (C400), and 700 g.m−2 coir (C700) GTX were installed firstly on 9° slope in “no-inf iltration” laboratory conditions, secondly on 27° slope in natural field conditions. The impact of GTX on runoff and soil loss was investigated to compare the performance of GTX in different conditions. Laboratory runoff ratio (percentage portion of control plot) equaled 78 %, 83 % and 91 % and peak discharge ratio equaled 83 %, 91 % and 97 % for J500, C700 and C400, respectively. In the field, a runoff ratio of 31 %, 62 % and 79 % and peak discharge ratio of 37 %, 74 % and 87 % were recorded for C700, J500 and C400, respectively. All tested GTX significantly decreased soil erosion. The highest soil loss reduction in the field was observed for J500 (by 99.4%) followed by C700 (by 97.9%) and C400 (by 93.8%). Irrespective of slope gradient or experiment condition, C400 provided lower runoff volume and peak discharge control than J500 and C700. The performance ranking of J500 and C700 in the laboratory differed from the field, which may be explained by different slope gradient and also by the role of soil, which was not included in the laboratory experiment.

Determination of actual soil sorptivity becomes one of the research preferences in the field of soil management and flash-flood protection. This Note presents an innovative approach to soil sorptivity determination. A single ring infiltration method, along with a simulation of rainfall of constant intensity, was used to measure ponding time t p. Hydraulic conductivity K was approximated from the analysis of the time series of the process of vertical non-steady cumulative infiltration appearing after the ponding time. Based on Philip's infiltration theory, a simple equation was derived in order to calculate sorptivity S from ponding time, rainfall intensity, and saturated hydraulic conductivity. Numerically determined results of S show to closely correspond with theoretical values published in the literature. To the best of our knowledge, this process of numerical determination of K and S has not been published so far. Moreover, unlike the traditional methods, e.g. single or double-ring in filtration experiments, this method provides more precise and representative values of S, verified by ponding time, as the results refer to the original soil sorptivity, not the sorptivity determined after the ponding time (meaning sorptivity of the fully saturated environment) which tends to reach zero. Our assumption was definitely confirmed by field experimental determination of ponding time and selected soil hydrology characteristics.