Interactions between fluvial processes and vegetation along the natural channel margins have been shown to be fundamental in determining meandering rivers development. By colonizing exposed sediments, riparian trees increase erosion resistance and stabilize fluvial sediment transport through their root systems, while during a flood event the above-ground biomass interacts with the water flow inducing sediment deposition and altering scour patterns. In turn river dynamics and hydrology influence vegetative biomass growth, affecting the spatial distribution of vegetation. These bio-morphological dynamics have been observed to direct control accretion and degradation rates of the meander bend. In particular, vegetation encroachments within the point bar (i.e. colonizing species and strand wood), initiate pioneeristic landforms that, when evolving, determine the lateral shifting of the margin that separates active channel from river floodplain and thus inner bank aggradation (bar push). This diminishes the portion of the morphologically active channel cross-section, influencing the erosion of the cutting bank and promoting channel widen- ing (bank pull ). As a result of the cyclical occurrence of these erosional and depositional processes, meandering rivers floodplain show a typical ridge and swale pattern characterized by the presence of complex morphological structures, namely, benches, scrolls and chutes within the new-created floodplain. Moreover, difference in migration rate between the two banks have been observed to induce local temporal variations in channel width that affect river channel morphodynamics and its overall planform through their influence on the local flow field and channel bed morphology. Despite enormous advances in field and laboratory techniques and modelling development of the last decades, little is known about the relation between floodplain patterns and their controlling bio-morphological interactions that determine the bank accretion process. This knowledge gap has so far limited the development of physically-based models for the evolution of meandering rivers able to describe the lateral migration of banklines separately. Most existing meander migration models are indeed based on the hypothesis of constant channel width. Starting from this knowledge gap, the present doctoral research has aimed to provide more insight in the mutual interactions among flow, sediment transport and riparian vegetation dynamics in advancing banks of meandering rivers. In order to achieve its aims, the research has been designed as an integration of remote sensing and in-situ field observations with a mathematical modelling approach to i) provide a quantitative description of vegetation and floodplain channel topography patterns in advancing meanders bend and to ii) explore the key control factors and their role in generating the observed patterns. The structure of the present PhD work is based on four main elements. First, two types of airborne historical data (air photographs and Lidar survey) have been investigated, in order to quantify the effects of spatial-temporal evolution of vegetation pattern on meander morphology and to provide evidence for the influence of vegetation within the topography of the present floodplain. Such remote sensing analysis has highlighted a strong correspondence between riparian canopy structure and geomorphological patterns within the floodplain area: this has clearly shown the need to interpret the final river morphology as the result of a two-way interaction between riparian vegetation dynamics and river processes. Second, field measurments have been conducted on a dynamic meander bend of the lower reach of the Tagliamento River, Italy, with the initial aim of checking the outcomes of the remote sensing analysis through ground data. The outcomes of the field measurements have further supported the results, providing ground evidence on the relations between vegetation and topographic patterns within the transition zone that is intermediate between the active channel bed and the vegetated portion of the accreting floodplain. The influence of vegetation on inner bank morphology has also been interpreted in the light of the expected time scales of inundation and geomorphic dynamics that characterize the advancing process of the inner bank. The combined analysis of both remotely sensed data and field measurements associated with the historical hydrological dataset have allowed to quantitatively characterize the biophysical characteristics of the buffer zone, close to the river edge, where the accretion processes take place. The third research element has foreseen the development of a biophysically-based, simplified bio-morphodynamic model for the lateral migration of a meander bend that took advantage of the empirical knowledge gained in the analysis of field data. The model links a minimalist approach that includes biophysically-based relationships to describe the interaction between riparian vegetation and river hydromorphodynamic processes, and employs a non linear mathematical model to describe the morphodynamics of meander channel bed. Model application has allowed to reproduce the spatial oscillations of vegetation biomass density and ground morphology observed in the previous analyses. Overall, the model allows to understand the role of the main controlling factors for the ground and vegetation patterns that characterize the advancing river bank and to investigate the temporal dynamics of the morphologically active channel width, providing insights into the bank pull and bar push phenomena. The fourth and concluding element of the present PhD research is a analytical investigation of the fundamental role of unsteadiness on the morphodynamic response of the river channel. Results obtained in the previous elements have clearly showed the tendency of a meander bend to develop temporal oscillations of the active channel width during its evolution, but no predictive analytical tool was previously available to investigate the channel bed response to such non-stationary planform dynamics. A non linear model has therefore been proposed to investigate the effect of active channel width unsteadiness on channel bed morphology. The basic case of free bar instability in a straight channel has been used in this first investigation, which has shown the tendency of channel widening to increase river bed instability compared to the steady case, in qualitative agreement with experimental observations. Overall, the research conducted within the present Doctoral Thesis represents a step forward in understanding the bio-morphodynamics of meandering rivers that can help the development of a complete bio-morphodynamic model for meandering rivers evolution, able to provide support for sustainable river management.

Over the past 200 years, rivers in industrialized countries have been significantly altered by human interventions such as channelization, hydropower development, and sediment mining causing observable biogeomorphological changes. In the European Alpine region, many large rivers have been impounded and channelized, yet few studies have conducted in-depth research on the temporal patterns of the causes and trajectories of these biogeomorphological responses, in comparison to rivers that can adjust their planform. Moreover, it is well-known that within channelized rivers alternating bars may appear due to an instability of the riverbed, but the development and influence of vegetation on such bars, its feedbacks on the morphodynamics of the bars and the degree to which these mutual interaction processes responds to anthropic stressors related to alterations in the flow and sediment supply regimes has received little attention. The present research aims to disentangle the mechanisms that may determine dramatically diverging biogeomorphological trajectories in regulated Alpine rivers. It further intends to identify the underlying relations of the triad that connects vegetation – sediment – flow regime and its feedbacks in regulated, channelized, rivers with vegetated bars. The methodology comprises an interdisciplinary approach which combines field and historical investigations with theoretical predictions, and integrates a variety of spatial and temporal scales and different levels of detail in characterising processes. Two case studies in the Alpine region (the Isère river in southeast France and the Noce river in northeast Italy) were selected for a quantitative, historical analysis of the bio-morphological trajectories using remotely sensed data to investigate the apparent responses to human-induced modifications of natural processes. Both rivers have been heavily impacted, with a notable increase of human stressors since the mid-20th century which can be associated with the transition of both systems from an initial, stable dynamic state characterized by bars having only sparse colonizing vegetation with a frequent turnover to a new, apparently stable state characterised by reduced morphodynamics and an increased vegetation cover in recent decades. The Isère river, which underwent a shift from unvegetated, migrating bars to vegetated, stable bars, was further explored with a hydromorphodynamic modelling approach to investigate historical changes in riparian vegetation recruitment and survival related to changes in the flow regime. The Windows of Opportunity model was successful at revealing temporal changes in recruitment conditions in response to flow regime alterations. Further results indicated a reduction in relevant high flow events that might be competent to induce large bar migration in the system. Alterations of the flow regime are assumed to have played a major role in vegetation encroachment directly by affecting vegetation recruitment through reduced flow disturbances and indirectly inducing modifications of bar morphodynamics. Field observations of root development were also made on the Noce and Isère rivers, focusing on two species Salix alba and Phalaris arundinacea, with the aim of improving understanding of the role of roots on the presence and movement of vegetated bars. When comparing results from different sites, more predictable linear relationships between root properties and depth below the ground surface were associated with stronger flow regulation. Bar morphology (surface elevation or depth of sedimentation and sediment calibre) and flow regime were found to be the main drivers of root architecture. Furthermore, roots were found to have an important role in the stabilization of the bars with the ability to stabilise fine sediments trapped by the plant’s canopy during phases of bar aggradation. To understand the current state of channelized Alpine rivers, which often show diverging biogeomorphic features, it is necessary to understand the underlying interactions between flow, sediment, and vegetation dynamics. Only through investigating the historical biomorphological evolution of rivers and the main drivers of that evolution it is possible to design measures that can be effective in rehabilitating desired ecosystem functions that have been markedly modified by those state transitions. In summary, this study has provided novel, quantitative insights about the complexity of flow – vegetation – morphology interactions occurring in channelized river systems in relation to anthropogenic stressors causing alteration in their flow and sediment supply regimes. By integrating different approaches, this study has shown how these river systems can be highly sensitive to even small changes in the anthropogenic stressors, depending on the stage in their evolutionary trajectory, which is crucial to be detected to support the development of sustainable management strategies aimed at restoring or improving target riverine functions and processes.

Near-natural river corridors (NNRs) provide crucial habitat for a host of biota and support the survival of people and nature worldwide at multiple spatiotemporal scales. Furthermore, NNRs represent fundamental references for river conservation, management, and restration, offering the opportunity to investigate processes under minimal anthropic disturbances. However, in the Anthropocene large near-natural rivers are rare gems in Europe an worldwide, and knowledge of their dynamics and ecosystem services are often scarcedue to a lack of hydromorphological and ecological data, monitoring, and baseline studies. Despite the scarcity and fragmentation of pertinent studies, many national and international guidelines and directives point to NNRs as reference systems for conservation, management, and restoration targets. In this framework, this Ph.D. thesis investigates the value of NNRs in the Anthropocene with an interdisciplinary approach, bridging fluvial geomorphology and environmental planning disciplines to support freshwater management and conservation in international cooperation for development. The first part of the research activity is rooted in fluvial geomorphology and explores the spatiotemporal trajectories of NNRs adopting several remote sensing products, cloud computing, and geomatic. The recent morphological trajectory of the near-natural Vjosa River (GR/AL) is presented as the response of the river to multidecadal climatic oscillations and more recent localized anthropic pressures, warning about the importance of considering and quantifying the geomorphic sensitivity of river systems in management and conservation. Thus, we focused on framing remote sensing-based procedures for characterizing active river channel spatiotemporal dynamics in the Mediterranean biogeoclimatic region. The second part of the research activity deals with the need to improve riverscape science and landscape management dialogue and the valuation of river ecosystem services. Focusing on inland waters ecosystem services, we integrate a socio-cultural approach with spatial analysis for cultural ecosystem services supply assessment in selected Albanian Protected freshwater ecosystems, outlining the relevant role of ecotones in providing cultural ecosystem services and the multifacet value of such dynamic zones. The third part of the research activity strongly links fluvial geomorphology and environmental management and conservation. It proposes the reconstruction of in-channel vegetation age and related ecosystem services spatiotemporal trajectories in targeted reaches of the Vjosa (GR/AL) and Tagliamento (IT) NNRs, integrating cloud computing, multispectral images, and fieldwork data. Developed baseline knowledge and tools can support the study, management, and conservation of highly dynamic river corridors in Mediterranean temperate climates, and the proposed integrated and multidisciplinary set of approaches is promising to cope with data scarcity that often characterizes the few remaining near-natural rivers in the world.

During the past decades, the systematic investigation of the morphodynamics of meandering rivers mostly involved the theoretical-analytical methodology. The development of analytical models enabled the definition of equilibrium conditions, stability and evolution of river meanders and to investigate the interaction between planform and bedform processes and mechanisms. In recent years the new branch of remote sensing applied to river morphodynamics has been constantly developing simultaneously to the rapid increase of computational and satellite resources. The remote sensing analysis is nowadays employed in a wide range fields in geophysics; for this reason, the past years have seen the prolific development of numerous algorithms for remote sensing analysis. However, remote sensing of meandering river morphodynamics has not been consistently integrated with morphodynamic modelling so far. There is a lack of sophisticated algorithms for the extraction of extensive morphodynamic information from the available remotely sensed data; this gap prevented researchers from seeking systematic validation of analytical models to define their range of applicability, and to exploit their potential for improved insight on observations in real world meandering rivers. The evolutionary dynamics of the channel width, at local and bend scale, as well as the dynamics of bars in meandering rivers represent two major unsettled issues in our present understanding of river meandering dynamics. In this thesis I first provide a systematic methodology for the automated extraction of meandering river morphodynamic information from multitemporal, multispectral remotely sensed data, coded in the PyRIS software. Moreover, I develop an analytical model to investigate the long-term planform evolution of periodic sequences of meander bends incorporating spatio-temporal variations of channel curvature, width and slope. A first model component predicts the temporal evolution of the channel width and slope based on a novel treatment of the sediment continuity at the reach scale. A second model component is a fully analytical, evolutionary model of periodic meanders with spatially and temporally oscillating width accounting for nonlinear feedbacks in flow and sediment transport by means of a two-parameters perturbation approach. Application of the PyRIS software to several long reaches of free-flowing meandering rivers allows me to develop a consistent set of observations on the temporal and spatial evolution of channel width and curvature with unprecedented level of detail. Furthermore, model outcomes indicate that meander-averaged width and slope invariably decrease during meander development, and that the temporal adjustment of the hydraulic geometry is controlled by the ratio between the evolutionary timescales of planform and riverbed, quantified from the analyzed meandering rivers dataset. The nonlinear perturbation model indicates that width and curvature co-evolve according to a hysteretic behavior in time and predicts that the meander belt width dramatically decreases when the meander resonance threshold is crossed. The modelling approach predicts wider-at-bend meanders when the bank pull is dominant with respect to bar push, which in turn promotes meander bends that are wider at inflections. Analytical modeling and remote sensing analysis are mostly integrated through a statistical approach; bend-scale evolutionary analysis of planform descriptors such as channel width, width oscillations and curvature in large pristine meandering rivers exhibit good agreement with the outcomes of the proposed analytical models. Finally, the integration between analytical modeling and remote sensing analysis allows me to identify the key processes controlling the interaction between migrating sediment bars and planform-driven steady point bars. The conditions for the formation of migrating bars in meandering rivers are mostly related to the production of sediment supply by the basin, contrarily to the widespread idea that meandering rivers exhibiting migrating bars typically display lower values of the channel curvature.

NewAge-JGrass system for forecasting and modelling of water resources in general at the basin scale. As a modern hydrological modelling, it is composed of two parts: (i) the system for data and results visualization based on the Geographic Information System uDig and (ii) the component based modelling system. All the system is based on Java because of its portability. Java is a modern and mature language aware of the web and has features such as multithreading that are essential to build scalable modelling platform. There are a few open source frameworks available that allow adaptation for our task, such as the GeoTools project by the Open GIS Consortium, representing a solid foundation for spatial analysis. OMS was chosen for facilitating model connectivity because of it low invasiveness in code practice and capability in production of leaner and more descriptive modelling code . uDig as visualization/GIS platform, including GIS services, and its integration with the JGrass GIS, developed by http://udig.refractions.net/, offers a spatial toolbox which contains the features previously offered by JGrass. Compared to traditional hydrological models, which are built upon monolithic code, JGrass-NewAge allows for multiple modelling solutions for the same physical process, provided they share similar input and outputs constraints. Modeling components are connected by means of a concise scripting language NewAge-JGrass components can be grouped in several categories. The geomorphic and DEM analyses which solves the problem of basin delineation; the tools for making spatial extrapolation/interpolation of the meteorological data; the estimation of the radiation forcing; the estimation of evapotranspiration; the estimation of the runoff production; the channel routing and tools for automatic model parameter calibration such as DREAM, Particle Swarm and LUCA. NewAge requires interpolated meteorological variables (such as air temperature, precipitation, and relative humidity) as input data for each hillslope. They can be computed by a deterministic or geostatistic approaches. The energy model includes both, shortwave and longwave radiation calculation components for each hillslope. The first implements algorithms that take into account shade and complex topography and cloud cover. Evapotraspiration can be modelled using two different solutions: the Fao-Evapotraspiration model and the Priestley-Taylor model. A snow melting and snow water equivalent model is also part of the system. Duffy's model and Hymod model are the runoff production models implemented in NewAge. In both cases the model is applied for each hillslope. Finally, the discharge generated at each hillslope is routed to each associated stream link. Modeling solutions (connections of different components) are applied in three different river basin and verifications against measured data (discharge, radiation fluxes, snow water equivalent) are presented by using traditional goodness of fitting indices.

River/stream water temperature is one of the master water quality parameters as it controls several key iogeochemical, physical and ecological processes and river ecosystem functioning. Thermal regimes of several rivers have been substantially altered by climate change and other anthropogenic impacts resulting in deleterious impacts on river health. Given its importance, several studies have been conducted to understand the key processes defining water temperature, its controls and drivers of change. Temporal and spatial river temperature changes are a result of complex interactions between climate, hydrology and landscape/basin properties, making it difficult to identify and quantify the effect of individual controls. There is a need to further improve our understanding of the causes of spatiotemporal heterogeneity in river temperatures and the governing processes altering river temperatures. Furthermore, to assess the impacts of changing river temperatures on the river ecosystem, it is crucial to better understand the responses of freshwater biota to simultaneously acting stressors such as changing river temperatures, hydrology and river quality aspects (e.g. dissolved oxygen levels). So far, only a handful of studies have explored the impacts of multiple stressors, including changing river temperature, on river biota and, thus, are not well known. This thesis, thus, analysed the changes in river temperature behaviour at different scales and its effects on freshwater organisms. Firstly, at a regional scale, temporal changes in river temperature within long (25 years) and short time periods (10 years) were quantified and the roles of climatic, hydrological and landscape factors were identified for North German rivers. Secondly, at a reach scale, spatial temperature heterogeneity in a sixth-order lowland river (River Spree) was quantified and the role of landscape factors in inducing such heterogeneity was elucidated. Thirdly, at a site scale, short-term behavioural responses (namely drift) of three benthic invertebrate species to varying levels of water temperature, flow, and dissolved oxygen, and to combinations of those factors were experimentally investigated. Results from this thesis showed that, at a regional scale, the majority of investigated rivers in Germany have undergone significant annual and seasonal warming in the past decades. Air temperature change was found to be the major control of increasing river temperatures and of its temporal variability, with increasing influence for increasing catchment area and lower altitudes (lowland rivers). Strongest river temperature increase was observed in areas with low water availability. Other hydro-climatological variables such as flow, baseflow, NAO, had significant contributions in river temperature variability. Spatial variability in river temperature trend rates was mainly governed by ecoregion, altitude and catchment area via affecting the sensitivity of river temperature to its local climate. At a reach scale as well, air temperature was the major control of the temporal variability in river temperature over a period of nine months within a 200 km lowland river reach. The spatial heterogeneity of river temperature in this reach was most apparent during warm months and was mainly a result of the local landscape settings namely, urban areas and lakes. The influence of urban areas was independent of its distance from the river edge, at least when present within 1 km. Heat advected from upstream reaches determined the base river temperature while climatological controls induced river temperature variations around that base temperature, especially below lakes. Riparian buffers were not found to be effective in substantially moderating river temperature in reaches affected by lake warming due to the dominant advected heat from the upstream lake. Experimental investigation indicated that increasing water temperature had a stronger short-term effect on behavioural responses of benthic invertebrates, than simultaneous changes in flow or dissolved oxygen. Also, increases in water temperature was shown to affect benthic invertebrates more severely if accompanied by concomitant low dissolved oxygen and flow levels, while interactive effects among variables vary much among taxa. These results support findings of other studies that river warming, similar to climate change, might be a global phenomenon. Within Germany, lowland rivers are the most vulnerable to future warming, with reaches affected by urbanization and shallow lentic structures being more vulnerable and, therefore, requiring urgent attention. Furthermore, river biota in lowland rivers is particularly susceptible to short-term increases in river temperature such as heat waves. Plantation of riparian buffers, a widely recognized practice to manage climate change effects, in the headwater reaches can be suggested to mitigate and prevent future warming of lowland rivers in general and also throughout river basins, as river temperature response in lowland catchments is a culmination of local and upstream conditions. However, further river temperature increase in lowland river reaches within or close to urban areas and shallow lentic structures will be more difficult to mitigate only via riparian shading and would require additional measures

Braided rivers exhibit extremely complex and dynamic morphologies as their multiple channels are constantly re-worked. The research reported in this thesis explored a number of properties of braided river form and dynamics and some controlling factors through three individual but complementary research elements. The first research element was concerned with some of the controls on the transition between single thread and multi-thread channel patterns. Twenty-seven different flume experiments were conducted, supported by fourteen replicates. In these experiments, channel confinement (maximum possible channel width) and formative discharge were varied in a 25 x 2.9 m flume of constant slope (1%) and bed material (D50 = 1mm) with sediment supply constrained to match sediment output. As the maximum potential channel width increased, the channel pattern changed from a single channel with alternate bars, to the formation of mid-channel bars, and finally to a multi-thread braided pattern. Bed elevation frequency distributions showed distinct changes in their median, standard deviation, skewness and kurtosis as channel width and discharge increased, indicating the consequences of confining braided channels and regulating discharge on their bed elevation and morphology. The second and third parts of the research use remotely sensed data sets to explored (i) the degree to which a real river shows similar characteristics to those generated in the flume experiments and (ii) the variety in braiding patterns that are found in association with different boundary conditions of slope, width, discharge, and riparian vegetation. For the second research element, a Lidar survey of a 36 km reach of the lower Tagliamento river, Italy, was investigated. Within this reach, the river shows only small variations in slope and bed material size and is subject to the same flood flows. Analysis focused on thirty-six 1 km sub-reaches and demonstrated clear associations among the median, standard deviation, kurtosis and skewness of the bed and also clear downstream trends. Measures of vegetation cover showed statistically-significant associations with the median, standard deviation, kurtosis and skewness of the bed, particularly when only the 32 truly braided reaches were analysed. The measures of vegetation cover also showed downstream trends that corresponded with the trends in bed morphology. Overall, variations in bed morphology showed similar characteristics to those observed in the laboratory flume, but also they showed correspondence with riparian vegetation cover, indicating a topographic signature of vegetation on the bed morphology. The downstream trends appear to be associated with the changing vigour of the riparian vegetation and possibly variations in river baseflow characteristics associated with varying groundwater levels in the alluvial aquifer. The most mature patches of vegetation within the braid plain of the most downstream part of the 36 km reach appear to occur on remnants of braid plain isolated by river bed incision. The third and final research element considered the morphology of six European braided rivers of different slope, width, discharge and riparian vegetation type. Information extracted from Google Earth and other aerial imagery, and gauged river flow data supported an analysis of changes in braided river characteristics through time, and among the six European river sites. Four traditional planform indices were used to characterise the braiding pattern (Bi – braiding index, Ai and Ai2 –anastomosing indices; Si – main channel sinuosity) were combined with measures of stream power and its component variables (width, Q10, and slope). Robust data for bed material calibre was not available. Statistical analysis of the entire data set revealed a potential influence of riparian vegetation type on the relationship between unit stream power and braid channel width; and a trend of increasing Bi, Ai, Ai2, and Si with decreasing unit stream power. However, a larger and more complete data set is needed to confirm these general trends and to fully explore transitional rivers. This research has illustrated the morphological consequences of confining braided rivers and the dependence of the braiding pattern on stream power. It has also illustrated the role of vegetation in contributing to the morphological complexity of braided rivers and the potential role of riparian vegetation in constraining the relationship between stream power and braided river width.

The turbulent properties of flow in rivers are of fundamental importance to aquatic organisms yet are rarely quantified during routine river habitat assessment surveys or the design of restoration schemes due to their complex nature. This thesis uses a detailed review of the literature to highlight the various ways in which plants and animals modify the flow field, how this can deliver beneficial effects; and how turbulence can also generate threats to growth and survival. The thesis then presents the results from detailed field assessments of turbulence properties undertaken on low, intermediate and high gradient rivers to advance scientific understanding of the hydrodynamics of rivers and inform effective habitat assessment and restoration. A reach-scale comparison across sites reveals spatial variations in the relationships between turbulent parameters, emphasising the need for direct measurement of turbulence properties, while a geomorphic unit scale assessment suggests that variations in turbulence at the scale of individual roughness elements, and/or within the same broad groupings of geomorphic units (e.g. different types of pools) can have an important influence on hydraulic habitat. The importance of small-scale flow obstructions is further emphasised through analysis of the temporal dynamics of turbulence properties with changes in flow stage and vegetation growth. The highest magnitude temporal changes in turbulence properties were associated with individual boulders and vegetation patches respectively, indicating flow intensification around these sub-geomorphic unit scale features. Experimental research combining flow measurement with underwater videography reveals that more sophisticated turbulence parameters provide a better explanation of fish behaviour and habitat use under field conditions, further supporting direct measurement of turbulent properties where possible. The new insights into interactions between geomorphology, hydraulics and aquatic organisms generated by this work offer opportunities for refining habitat assessment and restoration design protocols to better integrate the important role of turbulence in generating suitable physical habitat for aquatic organisms.

Braided rivers represent one of the most complex forms of natural streams. Characterized by intense bed-load transport and highly dynamic channels, they carry significant naturalistic value and support a multiplicity of ecosystem services. Anthropogenic stressors and environmental changes put under stress hydro-morphological dynamics, biological processes, and ecosystem functioning and services of these fragile environments, necessitating integrated management and conservation strategies to preserve their biodiversity and ecological integrity. From a regulatory perspective, the two European Directives 2007/60/EC (the Floods Directive) and 2000/60/EC (the Water Framework Directive) identify and promote win--win measures that both reduce hydraulic risk and enhance the quality of water bodies. Some examples of win--win measures are river naturalization projects that not only restore river ecosystems to their natural state, enhancing biodiversity and ecosystem services but also provide flood protection, improve water quality, and offer recreational opportunities for local communities. This thesis contributes to the development of scientific knowledge in the previously mentioned areas, facilitating the know-how transfer of expertise from academia to the public institution. Building on these premises, this thesis aims to provide additional insights into the morphodynamics of braided rivers, offering new perspectives on the evolution of morphological indices during flood events and contributing valuable knowledge on how these complex systems respond to external stressors. The PhD thesis has been structured along three parts. The primary goal was to develop an innovative unsupervised algorithm for extracting the spatial and temporal evolution of braided river morphology. This computational framework is tailored for Sentinel--1 Synthetic Aperture Radar (SAR) data, overcoming the limitations imposed by weather conditions and day--night cicles. Moreover, it can be effortlessly adapted to additional SAR imagery databases. In cases where the water class covers only a minimal area of the entire scene, the histogram primarily represents the dry soil class. The framework faces this challenge employing a Self-Adaptive Thresholding Approach (SATA) to achieve a distinct bimodal distribution, enabling the accurate computation of threshold values for the 'dry soil' and 'water' classes. The tool, developed within the Python--API of Google Earth Engine (GEE), allowed us to assess the intra--event inundation dynamics, the estimation of the relationship between hydrometric level and wet area extension, and the assessment of bank erosion phenomena. The second chapter focuses on analyzing how morphological indices, such as the Total Braiding Intensity (TBI) index defined as the number of active channels, the Maximum Channel distance (MCD) defined as the distance between the most external channels, and the Cross-Sectional Cumulative Wetted Area (WA) defined as the sum of the wet area of all chanels in a cross section, correlate with discharge variations during flood events. To achieve this objective, the framework designed for Sentinel--1 images was adapted for use with high--definition imagery from the Italian COSMO--SkyMed satellite constellation. Leveraging the superior ground resolution of 3x3 meters provided by the Italian COSMO--SkyMed satellite constellation, we successfully segmented narrow secondary branches that remained undetected with Sentinel--1's 5x20 meter resolution. Thus obtained, the temporal evolution of the braiding system, enables us to evaluate the temporal evolution and the relationship between the TBI, MCD, and WA indices with increasing discharge values. The last part of the PhD thesis, deals with the assessment of the river bed grain size. The initial concept behind this PhD work was to analyze the potential of Synthetic Aperture Radar (SAR) data in assessing not only river morphology but also the pattern of patches with different grain size. While the initial two parts of the work addressed this, the final section's analysis of SAR data, unfortunately, did not provide significant results. Nevertheless, the subjects of surface roughness and the creation of spatially distributed grain size maps continue to hold significant scientific value in the fields of hydraulic and eco--hydraulic modeling and a key information for river management and renaturation projects. The principal role of this factor led us to slightly shift the research focus towards a detailed investigation of these elements, utilizing orthophotos, digital imagery, and corresponding analytical methods to model patterns of river roughness and grain size. A map illustrating the spatial pattern of grain size at the river reach scale was produced through regression analysis. This analysis correlated the texture properties derived from orthophoto tiles with the d50, d84, d90, and d95 grain size characteristics obtained from digital images, thereby providing considerable support for the implementation of detailed hydraulic models.

Hydropower plants, in particular High-head Hydropower Plants (HPPs), are an important source of energy also for their role in covering the daily peaks of energy demand. However, HPPs, especially storage power plants, have several negative effects on the ecosystems of downstream watercourses inducing unnatural changes in flow regime (hydropeaking). One way to study ecological implications induced by hydropeaking is represented by the coupling of hydrodynamic models (CFD) with habitat suitability models, in which hydrodynamic parameters are typically used to describe the physical habitat of indicator species. The research activity wanted to investigate possible differences between the use of 2D and 3D CFD approaches to determine the watercourse hydraulic characteristics and their effects on habitat evaluations, performed with CASiMiR software, in complex morphology as usually presents in hydropeaked reaches. In particular the habitat suitability for the two case studies (Valsura River and Rio Selva dei Molini), is analysed comparing different approaches for the reconstruction of the velocity field (depth-averaged velocities from 2D modelling, bottom velocity field reconstruction with log-law approach from 2D modelling and bottom velocity field from 3D modelling). The results show that the habitat suitability index (HSI) using 2D or 3D hydrodynamic models can be significantly different. Considering the entire flow range of hydropeaking events, the habitat simulations with bottom flow velocities from 3D modelling provide suitable habitats over the entire flow range representing the availability of stable suitable habitats. The results from the hydraulics and habitat analyses are used to investigate the effects of a hydropeaking mitigation project on the Valsura River (realization of a compensation bypass tunnel to decrease the peak flow rate and to remodel the up and down flow ramping rates) and on Rio Selva dei Molini (morphological measures to reduce the hydropeaking effects).