Post-dam channel adjustments of the Tammaro River (southern Italy)

The Tammaro River is the main right tributary of the Calore River(southern Italy). It is mostly an alluvial river, approximately 78 km-long. The basin is 673 km2-wide and mainly shaped into Miocene-aged flysch deposits. Agricultural areas strongly prevail over forests. Nowadays, the river is dammed in proximity of the Campolattaro village. The building of the Campolattaro Dam started in 1981 and was completed in 1993. After this year, several tests were carried out, but the dam started to work definitively only in 2006, due to several landslides that triggered on the western slope of the reservoir basin. This study compares the channel morphology of the Tammaro River in 1955, i.e. before the building of the Campolattaro Dam, with the morphology in 2004, i.e. after the tests, with the aim to investigate the channel adjustments experienced by the river in the investigated time-span. The study was carried out by introducing into the ArcGis 9.3 software both 1:25,000-scale topographic maps, dated back to 1955 and produced by Italian Geographic Military Institute (IGMI), and 1:5,000-scale color orthophotos, provided by Regione Campania. Both the topographic maps and the orthophotos were geo-referenced in the Italian Gauss-Boaga coordinate system. To improve and check the analysis of the topographic maps and aerial photos, also 1:25,000-scale topographic maps, derived from an updating, which was carried out in 1992, of the IGMI topographic maps of 1955, and 1:5,000-scale color orthophotos, dated back to 1998 and provided by Regione Campania, were introduced into the GIS software. The active channel, the centerline and the valley axis were manually digitized and automatically measured by the software. Similarly, fluvial bars were manually digitized and classified and their number and extension were automatically quantified. Finally, the obtained results were checked and/or integrated by means of a detailed geomorphological field survey. The results showed that the Tammaro River underwent a sharp narrowing, together with a slight increase of the sinuosity. These adjustments were more remarkable in the reaches located upstream to the Campolattaro Dam than downstream. A marked decrease in the fluvial bars area, coupled with an increase in their number, was also detected. Field evidence of riverbed lowering was also quite widespread. The channel morphology generally changed from transitional with slight or moderate incision to single thread. Such adjustments were coherent with those experienced by most part of the Italian rivers in the second half of the last century.