Vincenzo Palmeri

Despite growing interest in biochar as a soil amendment, its effects on erosion control remain uncertain, particularly for rill erosion. In this investigation, the short‐term (i.e., 1 month after biochar addition) effects of wood‐biochar on rill erosion and flow resistance were evaluated. At first, plot experiments were performed discharging a constant clear inflow into a rill incised in the original soil (rill ₀ ) and two rills, named rill ₃ and rill ₅ , incised in clay loam soil amended with different initial biochar concentrations BC (3% and 5% by weight). For each rill, the outflow discharge of the entire run was collected by a storage tank and the run was stopped when a 55 L volume was reached. The collected volumes were used to measure the corresponding weights of the eroded mixture (sediments and biochar), biochar and sediments. 3D photo reconstruction was used to obtain the Digital Elevation Models (DEM) before and after the runs and by the corresponding DEM of difference, the total volume of the eroded mixture was calculated. Measurements of water depth, hydraulic radius and flow velocity were used to calculate the Darcy–Weisbach friction factor f values. The results demonstrated that in the short term, the addition of BC = 3% is effective in reducing soil erosion by 9% as compared to the control condition, while adding BC = 5% determined an increase of 140% in eroded volume as, for this latter, the short‐term soil particle aggregation effects are too weak and the mixture remains cohesionless. Moreover, the analysis demonstrated that the proposed flow resistance equation gives a reliable f estimate and this equation gives, for fixed hydraulic conditions, flow resistance that decreases with increasing BC . Ultimately, for the short term, BC higher than 3%–4% cannot be considered a good soil conservation practice.

Purpose: Even though rill erosion is strongly influenced by flow hydraulics, slope, and channel tortuosity, the influence of path tortuosity on rill flow resistance and soil erosion has been investigated little. In this study, experiments on tortuous rills were performed on a plot with a mean slope s _p of 15% filled with clay soil to test a literature flow resistance equation previously proposed for tortuous rills and investigate if slope affects the potential link between rill tortuosity and soil loss. Methods: The four pre-shaped rills, characterized by designed tortuosity values t ₀ = 1, 1.08, 1.16, and 1.3, were subjected to a constant inflow discharge (0.3 L s ⁻¹ ), and the hydraulic variables were measured using the dye-tracing technique and 3D digital terrain models obtained by terrestrial surveys performed before and after the runs. Soil erosion volumes were quantified through DEMs (Digital Elevation Model) of difference. This analysis was also carried out for the experimental runs of a previous investigation with the same experimental setup and s _p = 11%. Results: The results confirmed that the literature flow resistance equation can be satisfactorily applied to estimate flow resistance in tortuous rills, and that tortuosity effects can be effectively captured by the a coefficient of the power velocity distribution regardless of the plot mean slope. The obtained results also revealed that lower slope (11%) unexpectedly produced higher flow velocities (except for the maximum tortuosity level) and soil losses, which can be mostly explained by the differences in channel bed roughness generated during the shaping phase. Conclusion: Overall, this study highlights that slope influences rill hydraulics and erosion for tortuous rills. These insights advance the understanding of rill dynamics and support the refinement of predictive models for soil conservation.

The use of appropriate models for environmental decision‐making is crucial for supporting soil conservation strategies, particularly in erosion‐prone systems such as Mediterranean basins. In this study, the suitability of the Sediment Delivery Distributed (SEDD) model at the event scale was evaluated in a 231 ha basin in Central Italy, where rainfall–runoff–sediment yield data from four erosive events were available. The model was applied by subdividing the basin into morphological units, defined as areas with uniform aspect, length, and slope steepness. Model parameterization involved the estimation of a single coefficient, β _e , embedded in the sediment delivery ratio of each morphological unit. The variability of β _e with rainfall–runoff event intensity was analysed. The resulting relationship reflects the physical mechanism whereby sediment transport along hillslopes becomes more efficient as event intensity increases, as represented by the runoff coefficient Q _R . Analysis of the empirical cumulative frequency distribution of the sediment delivery ratio for each morphological unit suggests that the influence of the runoff coefficient on β _e may vanish during the most erosive events. Under this hypothesis, for Q _R > 0.15, the variability of sediment delivery processes is governed solely by the structural component of sediment connectivity, while the functional component becomes invariant and characteristic of the investigated basin.

The effect of rock cover on rainfall impact and hydrodynamic flow behavior is a topic that needs to be further explored. In this paper, the effects of rock fragments embedded (trapped in the topsoil layer) in clay soil on runoff and sediment yield under simulated rainfall are investigated. The experiments were performed on 0.25 m × 0.25 m sloping microplots with bare soil (control) or a surface covered by 35 embedded rock elements (rock). For each configuration, three rainfall intensities (260.2, 444.0, and 605.2 mm h⁻¹), obtained by Kamphorst’s simulator, were tested, and the whole suspension was collected to determine runoff and sediment yield. The microplots were surveyed before and after the runs to obtain a Digital Elevation Model (DEM) and a DEM of Difference (DoD) and determine sediment yield. The obtained results demonstrated that both runoff and sediment yield (both measured from bowls and calculated from the DoD) increase with increasing rainfall intensity and rock percentage cover. For embedded elements, a higher rate of the sediments moving along the microplots reaches the downstream end of the microplot due to flow channelization. Finally, for the control condition, the erosive phenomena are concentrated under the nozzles, while for the rock configuration, they are also spread in the areas among the rock elements.

The knowledge of rill flow resistance is required to improve the modelling of upland erosion processes in different hydraulic conditions. Using controlled laboratory conditions, experimental runs in flumes are useful to investigate a specific effect, such as the boundary roughness, on flow resistance. In this paper, the effects of the soil roughness and roughness types on flow resistance are investigated using laboratory measurements. Flow resistance measurements, which were performed for rectangular fixed‐bed flumes with different bed and wall arrangements (smooth, covered by a clay‐loam, a sandy‐loam, a clay soil), were jointly used with literature measurements obtained for rectangular flumes covered by sand or grass. In agreement with previous studies, the analysis showed that, for open‐channel rill flows on a fixed bed, the influence of different soil grain roughness on the Darcy–Weisbach friction factor is restrained (≈ ±1%). On the other hand, the results highlighted that the effect of a different roughness type (i.e., sand or grass) on flow resistance is appreciable. Ultimately, laboratory measurements of flow resistance in a rectangular cross‐section flume are characterised by limited influence of soil grain roughness, and characteristic values of the roughness parameters in the flow resistance equation can be estimated for a non‐specific ‘soil roughness’ condition.

Although there is increasing interest in biochar as a soil amendment, its antierosive effectiveness is still uncertain. This investigation aims at evaluating how wood‐biochar affects rill erosion and hydrological connectivity in amended soils. In this paper, at first, plot experiments were performed entering a clear inflow into two rills, named rill₃ and rill₅, incised in a soil amended with an initial biochar concentration BC in weight of 3% and 5%, respectively. For each rill, terrestrial photogrammetry was used to obtain the Digital Elevation Models (DEM) before and after the experimental runs, and the consequent DEM of difference (DoD) was used to calculate the total volume of the eroded mixture (sediment and biochar), while three samples of rill outflow discharge were collected to determine the biochar and sediment rates. Then, small laboratory samples of the soil, biochar, and mixtures with different BC (1%, 3%, 5%, 10%, and 30%) were used to determine size and distribution of pores, and thus measure the structural and functional connectivity, by nuclear magnetic resonance (NMR) relaxometry with the fast field cycling (FFC) layout. The DoDs highlighted that the mixture volume for rill₅ was lower than that for rill₃. Moreover, the rill₅ condition yielded a higher biochar percentage in the mixture. The NMR measurements demonstrated that the biochar addition increases the size of micropores and mesopores, and the macro‐pore component is never dominant. Biochar concentrations greater than 5% do not produce appreciable changes in the pore distribution inside the mixture. The biochar component improves the structural connectivity up to BC = 5%. In the BC range of 0%–3%, FCI decreased as BC increased. In conclusion, a target biochar concentration of 5% allows for the mitigation of the rill erosion phenomena, favours the improvement of soil structural connectivity, and does not appreciably modify the functional connectivity.

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.

Rill erosion is a major issue on a global scale, and predicting the presence, position, and development of erosive forms on hillslopes is a significant challenge for the scientific community. Several plot-scale investigations confirmed the reliability of the terrestrial photogrammetric (TP) technique for studying rill erosion and the reliability of a method for extracting the rill network from Digital Surface Models (DSMs) and measuring the corresponding volume. In this paper, for an intense erosive event that occurred at the Sparacia experimental area (Sicily, Southern Italy), TP surveys of three plots, with different length and steepness, incised by rills, were performed to reconstruct the DSMs. For each plot, the rill network was extracted from the DSMs, and the non-contributing network was distinguished from the contributing one, from which the soil loss and the consequent eroded volumes V were determined. The specific aims were to (i) establish the effect of plot steepness on rill depths and some morphometric characteristics of the drainage rill network; (ii) test and calibrate the relationship between V and the total rill length L, using all rill measurements available in the literature and those obtained in this study; and (iii) modify the V–L relationship by including climate forcing and assessing the related performance. The rill depths, h, the drainage frequency, and drainage density of the rill networks detected in the three plots were compared. The analysis demonstrated that h and the morphometric parameters of the contributing rill network increase with plot steepness s. In particular, the mean depth increases from 2.79 to 4.85 cm for slope increasing from 14.9 to 26%. Moreover, the drainage frequency of the contributing rill network varies from 0.16 m⁻² for s = 14.9% to 0.47 m⁻² for s = 26%, while the drainage density of the contributing rill network varies from 0.92 m⁻¹ for s = 14.9% to 2.1 m⁻¹ for s = 26%. Finally, using the data available in the literature and those obtained in this investigation, an empirical relationship between V and the total rill length L was firstly tested and then rearranged considering the event rainfall erosivity R_e. Including R_e in the rearranged equation guaranteed the best performance in V estimation.

The ‘hydrological connectivity inside the soil’ refers to both the spatial pattern inside the soil (structural component) and the physical–chemical process at a molecular level (functional component). Fast field cycling (FFC) nuclear magnetic resonance (NMR) relaxometry allows for measuring structural and functional connectivity by two suitable indexes named structural connectivity index (SCI) and functional connectivity index (FCI). In this study, FFC NMR relaxometry was applied to soils sampled in a very degraded environment (i.e., a badland area) to detect the capability of the measurement technique to distinguish the hydrological connectivity of these samples having different conditions (layer explored by roots, sparsely‐vegetated and bare soil). The relaxograms measured by the FFC NMR, using Proton Larmor frequencies in the range 0.01–10 MHz, were integrated and the resulting S‐shaped curves were analysed to obtain the connectivity indexes. Results showed that the ‘Sparsely vegetated’ sample is characterized by more small‐sized pores than the ‘Rooted’ one. The comparison between the ‘Sparsely vegetated’ and ‘Bare’ conditions pointed out that the presence of vegetation reduces the measured relaxation times and, as a consequence, the corresponding pore sizes and modifies the structural connectivity. The analysis also revealed that the three samples are characterized by similar values of SCI, which are independent of the proton Larmor frequency, while the FCI values of the ‘Bare’ soil are the lowest. Conversely, samples from soil with vegetation (‘Rooted’ and ‘Sparsely vegetated’) present comparable functional connectivity. Finally, the analysis of the frequency distribution of the ratio of each connectivity index and its mean value (SCI/m(SCI) and FCI/m(FCI)) allowed to establish its normal distribution. For the investigated samples, this result established that FCI and SCI can be represented by their mean value.