Vincenzo Pampalone

Estimating the USLE Soil Erodibility Factor in Sicily, South Italy

The Universal Soil Loss Equation (USLE) is used by professionals and technicians to predict soil loss by water erosion and to establish soil conservation measures. One of the key elements of the USLE is the K factor, which is a measure of the soil erodibility. Given the difficulty in collecting sufficient data to adequately measure K, early in the USLEs history the soil erodibility nomograph method was developed to allow estimation of K based on standard soil properties. Since the nomograph approach was developed based on a small number of soils in the United States, it is necessary for other contexts to check the nomographs ability to predict the soils true erodibility. Considering that soil organic matter data are difficult to obtain, an estimation procedure of the soil erodibility factor, K, based only on soil textural data is desirable. In this investigation, the soil erodibility factor was first experimentally determined for the clay soil at the Sparacia (Sicily) experimental station. A relatively low value (0.039 t ha h ha-1MJ-1mm-1) was determined, and summer erodibility was found to be more than twice the value of winter erodibility. This measured K value was 1.85 times the nomograph K, which for many practical applications is not a large difference. Finally, using 1813 data points, a procedure for estimating K using only soil textural data was developed for Sicily. The errors of the predictions did not exceed a factor of two and three for 94.4% and 99.2% of the data points, respectively, suggesting a satisfactory ability of the developed procedure to yield an estimate of K with a reduced input dataset.

New Solution of Classical Hydraulic Jump

This technical note, applying dimensional analysis and incomplete self-similarity, proposes a new functional relationship for the sequent depth ratio for hydraulic jumps over both smooth and rough horizontal beds. For the smooth bed condition, experimental measurements in the literature were used to calibrate the new relationship. For the rough bed condition the data of a previous investigation were used with new measurements carried out in a rectangular horizontal flume having a gravel bed. Finally, a generalized solution of the sequent depth ratio is proposed.

Experimental Investigation of the Outflow Process over a Triangular Labyrinth-Weir

In this paper, the outflow process from a sharp-crested triangular labyrinth weir is studied. Applying dimensional analysis and the Π theorem, five dimensionless groups, describing the outflow process, are deduced. The measurements, carried out by using sharp-crested weirs placed in a flume, allowed to establish a dimensionless stage-discharge relation. According to this equation, the flow magnification is affected by either the length magnification ratio or head to one cycle width ratio. The proposed equation, which also satisfies two theoretical boundary conditions, was finally tested by using experimental measurements of different reservoir hydraulic models.

Testing the USLE-M family of models at the Sparacia experimental site in south Italy

AbstractThe modified Universal Soil Loss Equation (USLE-M) was empirically deduced by a statistical analysis of the original data set of soil loss measurements used to derive the Universal Soil Los...

Flow resistance equation for rills

In this paper a new flow resistance equation for rill flow was deduced applying dimensional analysis and self-similarity theory. At first the incomplete self-similarity hypothesis was used for establishing the flow velocity distribution whose integration gives the theoretical expression of the Darcy-Weisbach friction factor. Then the deduced theoretical resistance equation was tested by some measurements of flow velocity, water depth, cross section area, wetted perimeter and bed slope carried out in 106 reaches of some rills modelled on an experimental plot. A relationship between the velocity profile, the channel slope and the flow Froude number was also established. The analysis showed that the Darcy-Weisbach friction factor can be accurately estimated by the proposed theoretical approach based on a power-velocity profile.

Modeling Rill Erosion at the Sparacia Experimental Area

AbstractIn this paper, the contributions of rill and interrill components to total soil erosion monitored at event scale at the Sparacia experimental area, southern Italy, were first compared and the dominance of the rill component was detected. Then, the reliability of two empirical relationships between the rill length and its eroded volume and among the morphological variables (length, width, depth, and volume) describing the channelized process was tested using both direct measurements of rills, carried out for the October 3, 2011, event, and those of ephemeral gullies surveyed on February 2010 at Sparacia. The measurements of rills detected by the direct field relief were compared with those obtained using a survey that allowed the generation of a digital elevation model of the rilled area. Finally, plot rill erodibility values were estimated and their spatial and time variability were analyzed. Spatial variability of rill erodibility was negligible whereas a temporal variability was detected.

Establishing a Soil Loss Threshold for Limiting Rilling

AbstractIn this paper a frequency analysis of event soil loss measurements collected in the period 1999–2012 at the microplots and plots of the Sparacia Experimental Area in Sicily, southern Italy, was developed. The analysis was carried out using the annual maximum soil loss measurements normalized by the mean soil loss measured at a given temporal and spatial scale. The empirical frequency distribution of the normalized variable was well fitted by two Gumbel’s theoretical probability distributions discriminated by a value of the normalized variable equal to 2. This last value discriminates between the relatively low and frequent values of the normalized variable and the high and rare ones. The annual maximum soil loss was demonstrated to be representative of the total annual soil erosion at the Sparacia Experimental Area. Then, a threshold soil loss value at the annual temporal scale was calculated by multiplying the frequency factor, equal to 2, by the mean annual maximum soil loss values for each give...

Sequent Depth Ratio of a B-Jump

A B-jump is defined as the jump having the toe section located on a positively sloping upstream channel and the roller end on a downstream horizontal channel. This jump often occurs in the stilling basins with a horizontal bottom and located downstream of a steep channel. For a B-jump, a completely theoretical approach is not sufficient to solve the momentum equation and to establish the sequent depth ratio. In this paper, by using the laboratory measurements carried out in this investigation, some available empirical relationships useful for estimating the sequent depth ratio are tested. Then, by using the Π theorem of the dimensional analysis and the incomplete self-similarity theory, a generalized functional relationship for estimating the sequent depth ratio for different types of jumps is deduced. The estimate of the coefficient appearing in this relationship is dependent on the particular type of jump. In conclusion, the analysis established that the sequent depth ratio for a B-jump depends on a par...

Comparing theoretically supported rainfall‐runoff erosivity factors at the Sparacia (South Italy) experimental site

Hydrological Processes. 2018;32:507–515. Abstract Interpreting rainfall‐runoff erosivity by a process‐oriented scheme allows to conjugate the physical approach to soil loss estimate with the empirical one. Including the effect of runoff in the model permits to distinguish between detachment and transport in the soil erosion process. In this paper, at first, a general definition of the rainfall‐runoff erosivity factor REFe including the power of both event runoff coefficient QR and event rainfall erosivity index EI30 of the Universal Soil Loss Equation (USLE) is proposed. The REFe factor is applicable to all USLE‐based models (USLE, Modified USLE [USLE‐M] and Modified USLE‐M [USLE‐MM]) and it allows to distinguish between purely empirical models (e.g., Modified USLE‐M [USLE‐MM]) and those supported by applying theoretical dimensional analysis and self‐similarity to Wischmeier and Smith scheme. This last model category includes USLE, USLE‐M, and a new model, named USLE‐M based (USLE‐MB), that uses a rainfall‐runoff erosivity factor in which a power of runoff coefficient multiplies EI30. Using the database of Sparacia experimental site, the USLE‐MB is parameterized and a comparison with soil loss data is carried out. The developed analysis shows that USLE‐MB (characterized by a Nash–Sutcliffe Efficiency Index NSEI equal to 0.73 and a root mean square error RMSE = 11.7 Mg ha) has very similar soil loss estimate performances as compared with the USLE‐M (NSEI = 0.72 and RMSE = 12.0 Mg ha). However, the USLE‐MB yields a maximum discrepancy factor between predicted and measured soil loss values (176) that is much lower than that of USLE‐M (291). In conclusion, the USLE‐MB should be preferred in the context of theoretically supported USLE type models.

Testing the outflow process over a triangular labyrinth weir

AbstractIn this paper, the dimensionless stage-discharge relation for a sharp-crested triangular labyrinth weir, determined in a previous study, is initially tested by some experimental runs carrie...