Carmine Vacca (*) & Rocco Dominici (*)

(*) Dipartimento di Biologia, Ecologia e Scienze della Terra, Università della Calabria, cubo 15B, 87036 Arcavacata di Rende (CS). E-mail: carmine.vacca@unical.it

In Calabria region one of the main factors controlling the hydrological risk is the sediment transport of a stream. In this study, carried out by using the formula of Gavrilovi? (1972) in GIS environment, the average annual volume of sediment production for the catchment area of the F.ra Stilaro was calculated.
The formula W=T?h????(Z^3 )?S contains the following parameters: Temperature coefficient T=?((t'/10)+0,1) where t' is the average temperature, h mean annual rainfall (mm), S area of the watershed (km2) and Z coefficient of relative erosion =X?Y?(?+?Im) where X is the coefficient of soil cover; Y is the coefficient of soil resistance, ? is the coefficient of type and extent of erosion and Im the average slop of the watershed.
The calculation of the mean annual sediment yield W was performed by using bibliographic data such as the Geological map (1:25.000 scale sheet map, Cassa del mezzoggiorno), PAI (Autorità di Bacino Regione Calabria), use of the Soil (Corine 2000) and a 20 m DTM (Geoportale Nazionale). Temperature and annual precipitation from the period 1996-2005 (Center Multirischi-ARPACAL) have been considered for the calculation of T and h factors.
Data from different weather stations from 1920 to 2013 show a strong variability in relation to elevation, with a reduction in average rainfall and an increase in average temperatures from 1996 to 2005.
The values for X and Y were calculated based on qualitative description of the basin to which some numerical parameters defined by Zemljic (1971) correspond, while ? was calculated by integrating the database of the PAI (relating only to urban areas), with analysis of landslides in the areas (carried out by means of photo-interpretation and visual inspections).
Based on these data, the sediment retention coefficient (R) has been calculated in order to obtain the value (G) net of the sediment load redeposited at the watershed outlet. The application of the Gavrilovi? formula leads to a W value equal to 86789.63 mc / year and a value of G=W?R equal to 63166.34 mc / year.
The high meteo-climatic variability at the basin scale strongly controls the sediment yield as it modifies T, h and X, ? in a direct and indirect way respectively.
Referring to these elements, the estimation of sediment yield of F.ra Stilaro by applying the Gavrilovi? method must be carried out by the use of multi-temporal analysis in a GIS environment, supplemented by specific geo-morphological and litho-technical surveys.

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