Flow regime and geomorphic changes: statistical analysis of the Brenta River during the last 30 years

During the last decades, the most of European rivers have suffered intensive morphological changes. Geomorphic adjustments of rivers may be related to a natural (eg. hydrological regime) and anthropogenic response processes. Flood events cause large changes in a short time, and the European Directives require the mapping of risk areas and the improvement of the ecological river quality. To achieve these aims, it is essential to provide tool for forecasting river dynamics. This work has assessed the relationship that exists between river morphology, represented by active channel surface, and flow regime (last 30 years) of a middle portion of the Brenta River (~ 20 km). Geomorphic changes derived from interpretation of recent aerial photos (from 1981 to 2011) were evaluated and transformed into geomorphic variables. The Flow regime, measured at the Barzizza gauging station located 5 km upstream of the study reach, was analysed. Hydrological and morphological parameters organized into a single dataset were obtained. These two sets of data were analysed with measures of the relative goodness of fit of statistical regression models (“Akaike Information Criterion”) in order to assess whether the changes in the width of the channel and river island were due to the flow regime or to the floods occurrence. Results that the time and the sum of the discharge above the bankfull level, are significantly correlated with the morphological adjustments for both reach and sub-reach scale. The driving factor of the active channel widening is directly related to the flow regime, while the fluvial island increasing have a significant inverse relation with the time occurred. These variables can also be used for management purposes, as they can help to understand the future evolution of the watercourse.