Analysis of the River Isonzo discharge (1998-2005)

The River Isonzo is the largest river flowing into the Gulf of Trieste, a semi-enclosed basin located in the northeastern corner of the Adriatic Sea. Eight years of discharge and rainfall data (1998-2005) were collected from within the Isonzo watershed. Discharge was obtained at two locations, one at about 300 m downstream from the Solkan hydropower plant (Slovenia) and the other at Turriaco (Italy), at 13 km from the mouth. During 1998-2001, the mean flow was 91.2 m3/s at Solkan and 123.1 m3/s at Turriaco, with an annual cycle characterized by distinct maxima in spring and fall. From 2002 to 2005, the mean flow was weaker (about 68.7 m3/s at Solkan, 59.3 m3/s at Turriaco) and the peaks in the annual cycle were less distinct. Omitting the year 2003, that was exceptionally dry, similar results (74.4 m3/s at Solkan, 66.6 m3/s at Turriaco) were observed for the same period 2002-2005. Rainfall data was obtained at 6 locations (5 in Slovenia and 1 in Italy), and significant correlations between annual discharge and rainfall were found at most locations. The best correlations were found at stations with the highest annual rainfall (Socˇa and Kobarid), evidencing that, despite the damming, the River Isonzo discharge is strongly subject to the rainfall in the Slovenian territory.