A reliable prediction of event soil loss at the plot scale can be obtained by Universal Soil Loss Equation (USLE)-type models. For the Sparacia site (South Italy), the USLE-MB model was recently developed, in which the effect of the erosive agent is modeled using the rainfall erosivity index of the USLE by a power b₁ > 1 of the runoff coefficient Q_R. In this investigation, the model is parameterized separately using plot data collected for rill and interrill events that occurred in the Sparacia experimental area. The values b₁ = 1.406 and b₁ = 1.012 were obtained for the interrill and rill databases, respectively, which revealed a different effect of the runoff coefficient on soil loss due to the two erosive processes. Different relationships expressive of topographic factors were also deduced. The USLE-MB estimation performance significantly improved when operating the distinction between the two databases compared with the model parameterized on the complete database. The model was particularly reliable in estimating the highest event soil loss values, which were associated with the occurrence of rills. Finally, the proposed parameterization procedure lends itself to being tested in the framework of empirical soil loss modeling.

Water erosion is a significant global threat due to the high soil loss rate and all its consequent implications. Technologies to predict erosion are strongly related to measurements and vice versa. Measurements can simply provide empirical evidence of the erosion process and are hard to extrapolate in time and space. Measurements were used to develop some erosion models, such as the Universal Soil Loss Equation (USLE), and also for their calibration and validation. Several measurement techniques are used to collect soil erosion data at different spatial and temporal scales, but they cannot be considered fully accurate in any experimental condition. Each technique exhibits advantages and disadvantages, so extensive knowledge of their feasibility, accuracy, and limitations is required to correctly plan experiments and use the performed measurements. In this paper, recent scientific developments on the measurement of rainfall erosivity, soil loss at the plot scale, and rill and gully erosion using close-range photogrammetry are presented. Further considerations are made on the quality of soil erosion measurements and the usefulness and importance of measuring plot soil loss. Our critical analysis highlighted that the techniques reported in the literature are a solid basis, which, however, should be developed to improve their range of applicability and data quality.

Purpose: Soil loss estimation by the Universal Soil Loss Equation (USLE) – based approach is widely used to perform soil conservation interventions. The recently proposed USLE-MB model explicitly accounts for plot runoff coefficient in the erosivity factor. Both the USLE and the USLE-MB can be deduced using a reference condition given by the unit plot, which is characterized by fixed length, steepness and bare soil tilled along the steepest slope. There is little evidence about the existence of the unit plot among those used to develop the USLE model, and few investigations experimentally considered this condition later. Methods: In the present investigation, the USLE and USLE-MB models were parameterized using measurements performed in the Sparacia unit plots, in Sicily. Results: The USLE soil erodibility factor differed significantly from the nomograph value and also from the estimates previously obtained by two methods applied to measurements collected in plots having different length and steepness compared to the unit plot. The experimentally determined soil erodibility factor of the USLE-MB also differed from those determined with these two methods. The slope steepness factor determined according to its definition was not consistent with that estimated with known literature relationships. The slope length factor was nearly constant for the USLE and assumed to be constant for the USLE-MB, in contrast with the increasing relationship with the plot length suggested by the USLE. Conclusion: This investigation elucidated the discrepancy between the single factors of the models obtained using measurements from the unit plot and those otherwise estimated.

The results of the energetic characterization of two drip-type rainfall simulators, differing in the length of their capillary tubes, are presented. The rainfall kinetic power and momentum were measured using a single capillary tube and applying weighing and photographic techniques to determine the raindrop mean equivalent diameter and fall velocity, respectively. The measurements highlighted that the simulated rainfall intensity is the only variable affecting raindrop diameter, and the increase in the capillary tube length produces a reduction in rainfall intensity and raindrop diameter. Finally, an empirical relationship relating fall velocity with raindrop falling height and diameter found in the literature was developed and positively tested using both the experimental data of the velocity measurements from the present research and the literature. Relationships to estimate the rainfall kinetic power and momentum based on the knowledge of mass and raindrop falling height were proposed and positively tested for the two simulators in the present investigation. In conclusion, operative guidelines for a drip-type simulator characterization are proposed in this paper, considering that the knowledge of the geometric characteristics of the capillary tube, pressure head, and falling height values are fundamental to having a complete energetic characterization of the rainfall simulator.

The deduction of the weir flow stage-discharge relationship is a hydraulic problem generally solved by energy considerations and using the discharge coefficient to correct the gap between theoretical results and experimental measurements. In this context, the dimensional analysis represents an alternative to find simple and reliable equations to obtain the rating curve. In this study, the outflow process of vegetated weirs is investigated applying the Π-Theorem of dimensional analysis and the incomplete self-similarity theory. The aim of this paper is to propose a new theoretically-based stage-discharge relationship, and test its applicability by measurements recently published in the literature. The results showed that the errors in discharge estimate obtained by the proposed stage-discharge relationship are always less than or equal to ± 10% and less than or equal to ± 5% for 97–100% of cases. The main advantage of the proposed relationships is providing a single stage-discharge relationship, which has better performances than the equations reported in the literature and excludes the use of discharge coefficient.