Osservazioni su pluviometria e idrologia della Valle di Susa (Alpi Occidentali)

On precipitation and hydrology of Susa Valley (Western Alps)

Abstract

The Susa Valley is a transverse glacial valley belonging to the Cottian and Graian Alps. For this study, climatological and hydrological data from different sources have been collected and analysed. Monthly cumulated values of precipitations, discharge and hydrometric height have been calculated from daily data. Annual precipitation values result quite constant along the year within a range from 700 to 900 mm, with exception of Gad, a dry site (around 600 mm/y). The annual distribution of precipitation shows a bimodal trend, with a winter main minimum and an autumn maximum with secondary maximum in spring or summer according to the place considered. The pluviometric rate is thus subalpine or subcontinental. Peak discharge and hydrometric height maximum generally occur in March and in June, together with secondary maximum of precipitations and the melting of snow cover. Water resources in Susa Valley have been assessed on annual basis. By taking annual values for rainfall (isohyetal method) and runoff comparison, a water balance has been calculated at St. Antonino gauging station. Also on the basis of the lithologies outcropping on the area, it emerges that mean average precipitation (886 mm) are balanced by an evapotranspiration of 318 mm, a water runoff of 350 mm and a groundwater flow of 218 mm.