Abstract
Abstract. The theoretical TCEV (Two Component Extreme Value) distribution was applied to interpret the sediment yield datasets available in Southern Italy. The analysis is based on hydrological data collected for twelve catchments located in Calabria and Basilicata. A hierarchical approach was used to obtain a regional parent distribution which was used to determine the return time for each event. The hierarchical approach proposed in this study includes two stages. The first stage served for calibration and made it possible to estimate the parameters of the theoretical TCEV distribution. More specifically, the hypothesis of homogeneity with regard to the skewness coefficient and the coefficient of variation was verified using the datasets related to nine catchments. The second stage consisted in verifying the goodness of the theoretical distribution on three independent datasets provided by three experimental catchments not involved in the calibration. Overall results show that, even if the TCEV distribution was conceived to estimate peak flow, its concept of “double component” can be extended to predict sediment yield on a regional scale.
Highlights
Prediction of soil erosion and sediment yield, corresponding to a fixed return time, is necessary to adopt soil conservation strategies for reducing costs of on-site and off-site impacts in areas at risk.In Southern Italy, high rates of soil erosion and sediment yield are well documented both on cultivated land (Porto and Walling, 2012) and in areas covered by forests (Porto et al, 2004)
A recent study (Porto and Callegari, 2019), carried out on three experimental catchments (W1, W2, and W3) located in Calabria (Southern Italy), demonstrated that a significant proportion of the annual sediment yield in these catchments is due to the extreme event occurred each year which produced more than 50 % of the total annual sediment yield with a very few exceptions
Prediction of sediment yield generated by large events is very important in areas not covered by monitoring stations or for the areas with limited observational periods
Summary
Prediction of soil erosion and sediment yield, corresponding to a fixed return time, is necessary to adopt soil conservation strategies for reducing costs of on-site and off-site impacts in areas at risk.In Southern Italy, high rates of soil erosion and sediment yield are well documented both on cultivated land (Porto and Walling, 2012) and in areas covered by forests (Porto et al, 2004). Over the last 60 years, predictions of sediment yield are based both on the use of traditional monitoring techniques, such as observations on experimental plots or catchments, and on different types of models that vary from empirical-parametric approaches, such as SEDD (Ferro and Porto, 2000) or revised versions of the USLE (Cinnirella et al, 1998) to more recent physically- based models, such as WEPP (Nearing et al, 1989), whose goal is to simulate both the detachment and transport of soil particles Even if these models provide good estimates of long-term average values of sediment yield, they cannot make reliable predictions associated to a fixed return time especially if they are associated with extreme events.
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