Dinamica recente ed attuale di alvei fluviali: alcuni casi di studio appenninici (Italia centro-settentrionale)

Abstract

M.Rinaldi et al., Recent and present dynamics of river channels: some study cases from the Apennines (central-northern
Italy. (IT ISSN 0394-3356, 2008).
During the last decades and centuries, many fluvial systems of the world have been heavily impacted by various types of human disturbances. Regarding the Italian rivers, a bibliographic review carried out by Surian & Rinaldi (2003) pointed out two main types of channel adjustments (incision and narrowing) and proposed a classification scheme of the types and amount of channel adjustments. From more recent studies (Surian & Rinaldi, 2004) it is emerging that an inversion of trend in width adjustments (widening) and/or in bed-level adjustments (aggradation) have recently occurred in some study cases. Notwithstanding recent progress, there still remains the need to describe these processes more accurately and for a larger number of study cases. The research project PRIN 2005 "Present and recent dynamics of river channels in Northern and Central Italy: evolutionary trends, causes and management implications" has this general aim. This paper deals with changes and evolutionary trends of river channels in the Northern Apennines. The two main objectives of this research are: (1) to extend the knowledge of channel adjustments to new study cases in the northern Apennine; (2) to compare such study cases to define common trends of adjustments and differences eventually related to different geomorphic contexts and human impacts.
The following study cases have been selected, in order to represent different situations in the geographical context of central-northern
Apennines: (1) Magra River and its main tributary, Vara River; (2) Panaro River; (3) Cecina River, as a representative case of watershed
located in Southern Tuscany.
The following main aspects were investigated in detail:
1. Reconstruction of human interventions and disturbances in order to verify their possible role on the channel adjustments.
2. Analysis of channel changes. Most of the available maps and aerial photos were acquired and analysed in GIS, with the aim to allow
for comparisons and measurements of the planimetric parameters (channel width, sinuosity, braiding index). Then, a reconstruction of
bed-level changes through the comparison of topographic surveys from different years was carried out.
3. Field surveys. A series of forms for geomorphological field surveys were developed and applied to the study cases with a particular
focus on the interpretation and classification of channel adjustments.
The main results can be summarised as follows: (1) all study cases have been affected by channel bed incision, with the highest bedlevel lowering (up to 7-10 m) recorded along the Panaro River and the lower part of the Magra River; (2) similarly, all study cases have been affected by channel narrowing; (3) two phases of channel adjustment (incision - narrowing) can be distinguished, with the phase of major changes occurring between about '50s and the beginning of '90s; (4) such changes appear strongly connected to human factors, with quite evident cause-effect relations, and with the highest changes occurring along the rivers with strong human impact; (5) during the last 10-15 years, an inversion of trend of channel width is observed (widening phase, except for the Cecina River where the phase of channel narrowing is still continuing), coupled in some cases with situations of aggradation; however, during the last years (2006/07) a slightly new reduction in channel width is observed in some cases.