C. Di Stefano

SW—Soil and Water: Linking Clay Enrichment and Sediment Delivery Processes

Recent research has directed attention to the size distribution of eroded material because of its influence on deposition mechanics and in carrying capacity of pollutant materials. At first, in this paper the relationship between aggregate breakdown mechanism and erosion processes is briefly reviewed. Then the link between the clay enrichment ratio and the sediment delivery ratio at morphological unit scale is investigated. For 129 soil samples well distributed over the Sicilian Sparacia basin, the values for the experimental clay enrichment ratio calculated by the measured ultimate grain-size distributions are compared with the theoretical clay enrichment ratio values obtained by a procedure based on effective grain-size distribution. The clay content measurements, carried out in sediment samples drawn out from the sedimentation tank located at the basin outlet during the period February 1996–February 1997, are used to calculate the coefficient appearing in the relationship applied to estimate the sediment delivery ratio of each morphological unit. A relationship for estimating this coefficient using sediment clay content, measured by a conventional ultimate particle-size distribution, is also proposed. Finally, a Monte Carlo technique and caesium-137 measurements carried out in the experimental basin are used for verifying the accuracy of the sediment delivery distributed model which is strongly dependent on the estimate of the coefficient appearing in the sediment delivery ratio relationship.

Slope curvature influence on soil erosion and deposition processes

Sediment water quality problems are not necessarily the direct result of erosion from the most intense soil erosion areas. A study of within-basin variability of the sediment delivery processes is needed to identify areas where the most effective soil conservation strategies should focus. In this paper the sediment delivery processes is examined along the hydraulic path from sediment source areas to the nearest stream reach. The effects of shape (convex, concave, and uniform) of the hydraulic path are modeled using a power equation for slope profile and revised universal soil loss equation (RUSLE) with two different expressions of the topographic factors. A criterion is proposed for the erosion active slope length, i.e., the slope length in which no deposition processes occur. Then, using the continuity equation for sediment transport, a Ψ factor is deduced to correct the topographic factors of RUSLE and those proposed by Moore and Burch [1986], depending on slope curvature. Finally, two relationships for correcting the topographic factors for an irregular slope are experimentally tested comparing the calculated sediment yields with net soil erosion values estimated by the proportional method of Martz and de Jong [1987] and cesium 137 data available from a Sicilian basin.

Applying the bootstrap technique for studying soil redistribution by caesium-137 measurements at basin scale

Abstract The use of the bootstrap technique to estimate the reference level of137 Cs in an uneroded site is tested. The analysis is developed using 137Cs measurements made in a small experimental Sicilian basin. In the reference area the 137Cs activity is normally distributed with a known sample mean value, m equal to 94.4 mBq cm−2. The influence of137 Cs reference site sampling was determined generating samples having a fixed size, N and six different values of the sample coefficient of variation, CV, by a Monte Carlo technique. Then, for each size N, the probability distribution of the mean μ of the sequences generated by Monte Carlo technique is defined. The soil redistribution is determined, both at morphological unit and basin scale, using the proportional method of Martz & de Jong for calculating the net soil loss. The analysis showed that the spatial distribution of the net soil loss E i, and the basin value E b are independent of the sample size, N, and the coefficient of variation, CV, of the samples drawn from the reference area, if the bootstrap technique is applied for estimating the mean μ(μ) to use as reference value. The soil redistribution is also examined using as reference value the quantiles μ2.5, μ25, μ75, μ97.5 corresponding to a frequency F(μ) equal to 2.5, 25, 75 and 97.5%, respectively. In conclusion, the analysis established that a robust estimate of the reference value can be obtained even in fields where a small number of samples was drawn (high CV of the 137Cs activity of the field samples), using the bootstrap technique for generating sequences of reference values having known mean value m (the mean value of the 137Cs activity of the drawn field samples) and large sample size (N = 50).

Regular ArticleSW—Soil and Water: Linking Clay Enrichment and Sediment Delivery Processes

Recent research has directed attention to the size distribution of eroded material because of its influence on deposition mechanics and in carrying capacity of pollutant materials. At first, in this paper the relationship between aggregate breakdown mechanism and erosion processes is briefly reviewed. Then the link between the clay enrichment ratio and the sediment delivery ratio at morphological unit scale is investigated. For 129 soil samples well distributed over the Sicilian Sparacia basin, the values for the experimental clay enrichment ratio calculated by the measured ultimate grain-size distributions are compared with the theoretical clay enrichment ratio values obtained by a procedure based on effective grain-size distribution. The clay content measurements, carried out in sediment samples drawn out from the sedimentation tank located at the basin outlet during the period February 1996–February 1997, are used to calculate the coefficient appearing in the relationship applied to estimate the sediment delivery ratio of each morphological unit. A relationship for estimating this coefficient using sediment clay content, measured by a conventional ultimate particle-size distribution, is also proposed. Finally, a Monte Carlo technique and caesium-137 measurements carried out in the experimental basin are used for verifying the accuracy of the sediment delivery distributed model which is strongly dependent on the estimate of the coefficient appearing in the sediment delivery ratio relationship.

SW—Soil and Water

Recent research has directed attention to the size distribution of eroded material because of its influence on deposition mechanics and in carrying capacity of pollutant materials. At first, in this paper the relationship between aggregate breakdown mechanism and erosion processes is briefly reviewed. Then the link between the clay enrichment ratio and the sediment delivery ratio at morphological unit scale is investigated. For 129 soil samples well distributed over the Sicilian Sparacia basin, the values for the experimental clay enrichment ratio calculated by the measured ultimate grain-size distributions are compared with the theoretical clay enrichment ratio values obtained by a procedure based on effective grain-size distribution. The clay content measurements, carried out in sediment samples drawn out from the sedimentation tank located at the basin outlet during the period February 1996–February 1997, are used to calculate the coefficient appearing in the relationship applied to estimate the sediment delivery ratio of each morphological unit. A relationship for estimating this coefficient using sediment clay content, measured by a conventional ultimate particle-size distribution, is also proposed. Finally, a Monte Carlo technique and caesium-137 measurements carried out in the experimental basin are used for verifying the accuracy of the sediment delivery distributed model which is strongly dependent on the estimate of the coefficient appearing in the sediment delivery ratio relationship.