HYDRO-SEDIMENTARY DYNAMICS OF INTERMITTENT RIVER SYSTEMS: THE CELONE STREAM, PUGLIA (S-E ITALY)

This PhD thesis is carried out as part of a co-tutoring project between the University of L'Aquila and the Institute for Water Research (IRSA) of the National Research Council (CNR) based in Bari, it examines the erosion-transport-sedimentation dynamics of a small mediterranean watershed togheter with its ephemeral, intermittent river system. The data set consists of continuous discharge measurements (Q) and discrete concentration of suspended solids (SSC) samplings, collected at "Masseria Pirro" gauging station located 8 km upstream the Capaccio (Torrebianca) reservoir, and entirely managed by the institute. The flow-regime, the seasonality and the occurrence of particular events, will be studied as well as the total annual loads of suspended sediment calculated with different methods widely used in the literature. Subsequently, a statistical uncertainty analysis will be applied to these "output" data, aimed at assessing the reliability ranges related to each analyzed estimation method. From this last step one can already understands one of the fundamental purposes of the study, which is precisely to provide an instrument capable of making it clear that there is a certain "range", within which the applicability and repeatability of certain methods of evaluation rather than others, it may be more or less correct for some basins rather than others. Subsequently, starting from the results of the analysis carried out by addressing the load estimation problem and observing that, as in similar basins, also in Celone river most of the suspended sediment transported during the year is conveyed during flood events, we proceeded to analyze at the event scale the erosion-transport-sedimentation dynamic. After having obtained historical high resolution rainfall depth data, 30 min (± 0.5mm), of two different gauging stations belonging to the basin for the same study period (2010-2011) and after identifying a set of 18 independent variables, all competing in various capacities in influencing the studied phenomena, a Principal Component Analysis (PCA) was conducted, aimed at decreasing the variable’s space, reducing it to the only components, the main ones, which are most able to describe them. The event-scale analysis also made it possible to carry out a further study, concerning the Q-SSC hysteresis, or the nonlinear relationship that occurs during a single event between the variation in discharge and suspended sediment concentration, over time. This study, already carried out by De Girolamo et al. 2015, has been revived through the indexing of hysteresis cycles by the introduction of specific HI index. This methodology, even if it entails the loss of precision given by the observation of the single cycle in the traditional plot (Zhang et al. 2014), had the purpose of being able to make comparisons, both within the basin and with other basins, of different responses to different rainfall events. The application also made it possible to provide interesting indications regarding the location, more or less distant from the sampling point, of the sediment production areas, then compared with the results obtained by applying the FLORENCE model referred to in the subsequent chapter. Finally, a physically based modeling of the instrumented watershed was carried out, starting from it, through a subdivision into sub-areas unit with homogeneous characteristics and through further multi-scenario modelling applied to them, those areas of the basin most likely to release and convey sediment to the watercourse will be identified. The same model will make it possible to give a first approach quantification the of the reservoir siltation, for the Torrebianca reservoir itself (8km downstream of the measurement station on the Celone river). This quantification will then be validated through the aforementioned suspended load estimates.