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Meandering is one of the most common morphological pattern through which rivers manifest themselves. Here, the attention is devoted to meandering streams carving their path through permafrost floodplains, which typically characterize cold environments such as the Arctic. Despite meandering rivers have been widely studied in the last fifty years, little is known about the dynamics of streams where banks are composed of perennially frozen material. It is inquired whether there is a morphological signature in the planform of permafrost streams potentially deriving from specific thermo-mechanical processes occurring in Arctic landscapes, like the formation of thermo-erosional niches and sediment slumps caused by thaw-weakened soil. To this aim, a bend scale analysis of the planform geometry of several Arctic streams by means of Landsat satellite imagery is employed. Morphodynamic features such as lateral migration rates, channel curvatures, and width variations, are extracted from multispectral remotely sensed data by combining Google Earth Engine (GEE) with an established process-based software (PyRIS). Following a methodology based on continuous wavelet transform, a set of metrics quantitatively defining the meander shape, which include fattening and skewing coefficients, are used to compare permafrost streams with a series of natural meandering rivers from tropical and temperate regions obtained from the literature. The present analysis opens the way to a systematic integration between remote sensing and physically-based morphodynamic models able to incorporate thermo-mechanical processes uniquely related to permafrost environments.

While river channel change is a natural process for an alluvial river, increasing human activities such as sediment mining, construction of reservoirs and land use alterations can accelerate this process. Growing urbanization and socio-economic development in South-Eastern Europe over the last 30 years has shown a major impact on the river channel adjustments. New urbanization in Albania has rapidly developed after the collapse of dictatorial regime in 1990, with most rural population moving to the big cites, mostly the nearby capital Tirana and Durres. As consequence a boom in construction industry has occurred in this part of Albania, including new buildings and infrastructures. Rivers have been the primary source of building material. Here we analyse the channel adjustments that occurred on the Erzen River that passes nearby the two major urban centers of Tirana and Durres. The Erzen River has its origin at the Gropa mountain at 1200m asl, its length is 109 km, and it flows approximately westwards towards its mouth in the Adriatic Sea near the Lalzi Bay. The catchment area is 760 km2 and the mean annual flow is 18.1 m3/s. We analyse the incision and channel narrowing at lower part of the river by using remote sensing, historical image analyses, DEM and survey in the field. Major hydromorphological pressures potentially affecting the flow and sediment supply regime have been also analysed. Specifically, sediment mining has been reconstructed by identifying the mining sites in contact with the active river corridor between 1990-2015 along 30 km river length from aerial rivers, and from technical reports providing estimation of sand and gravel removed from the river.Our findings indicate rapid changes of channel morphology, with 20% up to 75% channel narrowing affecting the transitional and meandering reaches between 1968-2015 and high riverbed incision at the reach scale up to 5-6 m, which is also revealed by visual signs like increasing bed rock and bridge foundations exposure. Two cut-offs have been created at the meandering part of the river. Most of the main bridges in Albanian rivers have shown exposed foundation with 3-4 m on the last 15-20 years, where some of them are replaced by other bridges due to unstable structure condition. Compared with previous studies, narrowing and incision rates are among the highest observed in Europe after the 1950s. While on the upstream segment of the river two dams have been built, sediment mining appears as the main driving factors of the observed channel narrowing and incision. Twenty-two mining sites have been detected between 1995 - 2015 and 457,380 m3/year of sediments have been reported as withdrawn from the riverbed. The rapid channel incision has contributed to the increasing salty water intrusion and subsequent freshwater shortage in lowland part of the river. The observed narrowing and incision have likely played a key role also in the reduction of river sediment supply to the sea, which probably explains most of the very rapid coastal erosion that has been observed in the same period in the Lalzi Bay.

The construction of artificial reservoirs for hydropower production strongly alters sediment connectivity, which often produces significant impacts on the river reaches downstream morphology. Assessing sediment connectivity and transport variations is therefore crucial for predicting possible fluvial morphological trajectories and to define scientifically-based management practices in terms of water and sediment releases from Alpine reservoirs. For this reason APRIE, the agency responsible for hydropower regulation in the Trento Province (Italy), is carrying out a project to assess impacts caused by existing hydropower plants, in collaboration with the University of Trento.We focused on the study case of the Travignolo River, a tributary of the Avisio River in the Dolomites. The valley longitudinal connectivity has been completely interrupted by the Forte Buso dam construction in 1953 and by a series of smaller derivations from the main tributaries. We aim at understanding to what extent the presence of the dam affects the overall sediment connectivity, by assessing the relative contribution of sediment sources that currently drain into the lake with respect to the sources that are still connected to the Travignolo River, and by evaluating to what extent the disconnectivity has compromised the morphological equilibrium of the river.To this aim, structural and functional sediment connectivity are analysed through a three step integrated approach, considering connectivity at different spatial scales. First, fluvial morphological trajectories have been studied by investigating a dataset of historical images, which allowed us to identify both morphological changes and vegetation growth. Second, sediment connectivity has been modelled at the hillslope scale through the hydrological index of connectivity calculated by applying the SedInConnect model (Crema, S. & Cavalli, M., 2018, Computational Geosciences) on the basis of terrain elevation data and information on Quaternary deposits. The model allowed us to determine the potential sediment yield contribution from the different subbasins, as well as the position of sediment sources depending on their characteristic grain size. Finally, a quantitative analysis of sediment longitudinal connectivity has been carried on by applying the CASCADE Toolbox model (Tangi, M. et al., 2019, Environmental Modelling & Software) to the main river network of the Travignolo basin. Information on surface and subsurface grain size distribution have been obtained by collecting several samples along the main course of the Travignolo River and along their main tributaries, while channel width was estimated by analysing the high-resolution digital elevation model. To calibrate CASCADE model we have compared the predicted grain size distribution cascades with the measured subsurface composition. Furthermore, we have performed several simulations considering different methods of data spatialization and different choices of the main parameters, to obtain a general assessment of the model uncertainties.Results highlight the potential sediment contributions of different subbasins to the fluvial system, depending on their geological characteristics, slope and distance from the permanent drainage network. Moreover, the analysis of multiple scenarios reveals how sediment transport processes are strongly affected by the dam presence and how they may change depending on water delivery strategies.

We investigated the ecohydraulic effects of a recently implemented hydropeaking mitigation measure in the Upper Noce Stream (NE Italy, Italian Alps), which also allows for additional hydropower production. The Upper Noce, a 3rd order gravel-bed stream, was affected since the mid-1920s by storage hydropower production and associated hydropeaking. The mitigation measure consisted in the diversion of most of the released hydropeaks into a sequence of three newly-installed, cascading run-of-the-river power plants, fed by a penstock running almost parallel to the former hydropeaking reach. The hydropeaking-diversion mitigation measure markedly reduced hydropeaking on a 10-km stream reach, and hydropeaking is now released immediately upstream the confluence with a major free-flowing tributary, which increases the hydropeaking baseflow. The flow regime in the mitigated reach shifted from hydropeaking-dominated to baseflow-dominated regime in winter, with flow variability represented only by snowmelt and rainfall in late spring and summer. We applied two sets of indicators (the Hydropeaking Indicators HP1, HP2 and the COSH method) and conducted a simplified hydraulic analysis of the hydropeaking wave propagation. We assessed the ecological effects of the mitigation measure using three complementary data sources: the analysis of (a) the benthic and (b) hyporheic invertebrate communities, based on datasets collected before and after the implementation of the diversion measure, and (c) ancillary data monitored by the diversion plant manager for required environmental monitoring, which included the suspended sediment regime and the Extended Biotic Index, measured yearly from the year before to the four subsequent years after the implementation of the mitigation measure.Three main changes in eco-hydraulic processes associated with hydropeaking mitigation were detected. i) The flow regime in the mitigated reach changed to a residual flow type, with much less frequent residual hydropeaks, with an average two-fold increase in downramping rates that were recorded downstream the junction with a major tributary. ii) The functional composition of the macrobenthic communities shifted slightly in response to flow mitigation, but the taxonomic composition did not recover to conditions typical of more natural flow regimes. This was likely due to the reduced dilution of pollutants and resulting slight worsening in water quality. iii) The hyporheic communities conversely showed an increase in diversity and abundance of interstitial taxa, especially in the sites most affected by hydropeaking, and this effect was likely due to changes in the interstitial space availability, brought by an alteration of the previous time-space pattern of fine sediment transport, which eventually resulted in reduction of fine sediments clogging of the gravel bed interstices.Besides illustrating a feasible hydropeaking mitigation option for Alpine streams, this work suggests the importance of monitoring both benthic and hyporheic communities, together with the flow and sediment supply regimes, and physico-chemical water quality parameters, for carefully detecting changes in eco-hydraulic processes associated with hydropeaking mitigation that may not be fully expected in the design phase.

Climate change is already altering the hydrological regime of Arctic rivers. However, still little is known about fluvial morphological processes and trajectories in permafrost environments. In such iced floodplains, both hydrological and thermal regimes affect sediment transport and riverine morphological processes. Remote sensing represents a powerful approach to investigate fluvial systems in those isolated areas. Nevertheless, its application presents challenges linked to ice seasonality and the limited time window of the morphological activity, alongside the complex permafrost/river spatial patterns and related spectral signatures, which imply significant computational efforts. Addressing this, we propose an improved integration of existing tools for the spatio-temporal extraction of fluvial morphological indicators, combining in a unique working environment the cloud computing capability of Google Earth Engine (GEE) and a process-based tool for riverine multitemporal planform analysis (PyRIS). Fluvial morphological metrics have been extracted from a set of meandering rivers in the Arctic region, outlining the potential of anisotropic image filtering and image segmentation to enhance active channel detection in complex spatial-pattern areas. A 20-40% refinement in small object removal in river mask detection emerges. The synergy among existing instruments enhances the observation of natural river systems in permafrost environments, setting the basis for further studies on morphological processes and the evolution of such pristine and climatically-sensitive river systems.

Urban population has been increasing worldwide in recent decades and it is expected to continue growing in the coming years. Cities are facing the effects of the climate crisis, which primarily impact the most vulnerable contexts, first and foremost informal settlements. In this context, the growth of informal neighborhoods, home to one billion people1, poses complex challenges for the cities of today and tomorrow. In these urban areas traditional, informal and formal social dynamics coexist, strengthened by strong community identities and bonds. Major problems are due to the lack of basic services and infrastructure, making these areas more vulnerable to the increasingly frequent and intense extreme rainfall events. In this work, we present the recently launched Europeaid-funded project MUDAR (Mozambique integrated Urban Development by Actions and Relationships), and specifically focus on its component that addresses the dynamics and effects of flooding in an informal urban area: the Macuti neighborhood in the city of Beira, Mozambique. Macuti is situated on the coast, making it particularly vulnerable to frequent cyclones, one of all Idai, which damaged 49% of its buildings in March 20192. Moreover, it is located on a marshy, purely flat area at the end of an inadequate open drainage network serving the entire city, which is unable to drain the flow at high tide. Macuti, with its almost 17 thousand people (2017), since the early 2000s has been experiencing a rapid growth in spontaneous settlements, which has resulted in a higher population density, with the unbuilt area decreasing by 40% from 2004 to 2022, and soil permeability further reducing in a context where the clayey soil composition already strongly limits rainfall infiltration. These changes, in addition to the inadequate water infrastructure, have exacerbated flooding problems associated with heavy rainfall events (the maximum daily precipitation of the 1990-2020 period was 288.5 mm/day). Investigating the socio-hydrology of flooding in these informal settlements is particularly complex because its requirements for high-resolution topographic, soil, land use and meteorological data, which are very limited in these informal settlements. More specifically, we present preliminary outcomes and the proposed project strategy to cope with the intrinsic data scarcity of such context, which is based on carefully designed participatory surveys with local actors. To fill this data gap, a multi-disciplinary approach has been adopted by combining elaborations from satellite image processing (SAR) with in-situ measurements and interviews to inhabitants and professionals. In addition to being involved in providing information about the area, the inhabitants are a crucial actor in the decision-making process for choosing the technical solutions to be implemented. Preliminary results on flooding dynamics in Macuti neighborhood, as well as on three Nature-Based-Solutions scenarios emerging from the participatory process highlight promising factors that can allow adapting the participatory procedure in similar contexts. 1French, M., Trundle, A., Korte, I., Koto, C. (2020). Climate Resilience in Urban Informal Settlements: Towards a Transformative Upgrading Agenda. Climate Resilient Urban Areas, 129-1532UNOSAT-REACH (2019). Mozambique- Beira City -Macuti - Neighbourhood Damage Assessment- As of 26 March 2019. URL: https://m.reliefweb.int/report/3056948

We discuss the prioritization of river reaches to be selected for restoration measures under the constraints of financial resource limitation. We propose and apply a simple approach based on the quantification of major hydro‐morphological alterations and the critical comparison with locally proposed restoration actions. The available hydro‐morphological and ecological data for the approach do not go beyond the requirements posed by the implementation of the EU Water Framework and Floods Directives. We describe an example that refers to a heavily regulated Alpine river (Sarca River, NE Italy). The results indicate hydropower facilities as a key source of hydrological alteration, with sediment retention and grade control structures on lateral tributaries playing an additional relevant role in reducing sediment supply. The frequency and duration of sediment‐transporting floods have dramatically decreased, and the bed sediment composition has been markedly altered and become highly compacted. Habitat improvement has been achieved after the implementation of minimum environmental flows. The comparison between the results of the hydro‐morphological indicators and the locally proposed restoration actions highlights that reaches with lower degree of hydro‐morphological alterations do not coincide with the areas chosen for the locally planned actions, which often miss considerations of the relevant spatial scales. In a context of limited available financial resources and data compared to other flagship river restoration projects in the European Alps, the present work suggests viable options for the choice of target restoration reaches., Consorzio dei Comuni BIM Sarca, Italian Ministry of Education, University and Research (MIUR), Rete di Riserve della Sarca

Besides their environmental values, near-natural rivers offer the opportunity to observe and investigate riverine processes as they would occur under limited anthropic pressures, representing fundamental references for river management and restoration. Even so, few large near-natural rivers can still be found in Europe and worldwide, and their knowledge is often scarce due to a lack of hydromorphological monitoring and baseline studies. Among them, the Vjosa/Aoos River (GR, AL) has been recently recognized as a key large fluvial corridor and a significant model ecosystem. We investigate the catchment-scale recent morphological trajectories of the Vjosa river and its tributaries, coupling the reconstruction of channel adjustments over the past 50 years from remote sensing images with the analysis of possible drivers of change at the catchment and reach scale. We considered eight reaches in the main course of the Vjosa river as well as in some major tributaries (Sarandaporo, Drinos, Shushica) with different morphologies and confinement degrees. Our results underline the sensitivity of the Vjosa system to both hydrological alterations and human pressures. Specifically, it is possible to observe a response of the system passing from an intense period of high magnitude, frequency, and duration of flood events in the 1960s to a drier period in the following decades. To study the morphological response, three time periods are considered: 1968-1985, 1985-2000 and 2005-2020. In the first examined decades, river trajectories highlight the narrowing of the active channel as a primary response to the hydrological change in the majority of selected reaches, with a 20-50% active width reduction with respect to 1968. In the following time periods, the narrowing rate decreases at the catchment scale, while in the last phase the effect of human pressures in some reaches can be observed. Indeed, from the late 1980s, human pressures at different spatial and temporal scales can be identified, locally altering the natural trajectory of the affected reaches. Such pressures include sediment mining and extensive bank protection of the lowland reaches, together with flow regime alteration occurring in one headwater sub-catchment. However, our analysis reveals primarily a high sensitivity of the Vjosa system to recent climatic variations, suggesting the importance of accounting for future projected changes in rainfall regime in shaping morphological trajectories. The baseline knowledge on the morphological sensitivity and recovery time developed in this work provides an important reference for the management of highly dynamic river corridors in temperate and Mediterranean climates.

Confined meandering rivers are bounded between valleys and they are limited in their lateral migration compared to free meandering ones. In this study, we designed a model-based analysis to investi...

We study the morphodynamics of channel width oscillations associated with the planform development of river meander bends. With this aim we develop a novel planform evolution model, based on the framework of the classical bend theory of river meanders by Ikedaet al. (J. Fluid Mech., vol. 112, 1981), that accounts for local width changes over space and time, tied to the local hydro-morphodynamics through a two-way feedback process. We focus our attention on ‘autogenic’ width variations, which are forced by flow nonlinearities driven by channel curvature dynamics. Under the assumption of regular, sinusoidal width and curvature oscillations, we obtain a set of ordinary differential equations, formally identical to those presented by Seminaraet al. (J. Fluid Mech., vol. 438, 2001, pp. 213–230), with an additional equation for the longitudinal oscillation of the channel width. The proposed approach gives insight into the interaction between autogenic width variations and curvature in meander development and between forcing and damping effects in the formation of width variations. Model outcomes suggest that autogenic width oscillations mainly determine wider-at-inflection meandering river patterns, and affect their planform development particularly at super-resonant aspect ratios, where the width oscillation reaches its maximum and reduces meander sinuosity and lateral floodplain size. The coevolution of autogenic width oscillation and curvature occurs through temporal hysteresis cycles, whereby the peak in channel curvature lags behind that of width oscillation. Width oscillation amplitudes predicted by the model are consistent with those extracted from remotely sensed data.

This study investigates the dependency of meander lateral migration rates on the spatial distribution of channel centerline curvature in both synthetic and real meandering rivers. It employs Machine Learning techniques (hereafter ML) to relate observed local lateral meander migration rates with the local and the upstream/downstream values of the centerline curvature. To achieve this goal, it was primarily essential to identify the feasibility of using ML in the meandering river's morphodynamics. We then determined the ability of ML to predict the excess near bank velocity based a set of input data using different regression techniques (linear and polynomial, Stochastic Gradient Descent, Multi-Layer Perceptron, and Support Vector Machine). We then moved forward to study the upstream-downstream influence on local migration rate. Synthetic meandering river planforms, as obtained through the planform evolution model of Bogoni et al. (2017), which is based on Zolezzi and Seminara (2001) meander flow model, were used as test cases for the calibration and check of the different adopted ML algorithms. The calibrated algorithms were then applied to multi-temporal information on meander planform dynamics obtained through the PyRiS software (Monegaglia et al., 2018), to quantify to which extent the upstream and downstream distribution of meander centerline curvature affects the local meander migration rate in real rivers.References 1- Zolezzi, G., & Seminara, G. (2001b). Downstream and upstream influence in river meandering. Part 1. General theory and application overdeepening. Journal of Fluid Mechanics, 438(September 2015), 183–211. https://doi.org/10.1017/S002211200100427X2- Monegaglia, F., Zolezzi, G., Güneralp, I., Henshaw, A. J., & Tubino, M. (2018). Automated extraction of meandering river morphodynamics from multitemporal remotely sensed data. In Environmental Modelling & Software (Vol. 105, pp. 171–186). https://doi.org/10.1016/j.envsoft.2018.03.0283- Bogoni, M., Putti, M., & Lanzoni, S. (2017). Modeling meander morphodynamics over self-formed heterogeneous floodplains. In Water Resources Research (Vol. 53, Issue 6, pp. 5137–5157). https://doi.org/10.1002/2017wr0207264- Benozzo, D., Olivetti, E., Avesani, P. (2017). Supervised Estimation of Granger-Based Causality between Time series. In Frontiers in Neuroinformatics. https://doi.org/10.3389/fninf.2017.00068 5- Sharma A., Kiciman, E. (2020). DoWhy: An End-to-End library for Causal Inference. arXiv preprint arXiv:2011.04216. https://arxiv.org/abs/2011.04216

Restoration of spawning and juvenile habitats is often used to restore fish abundances in rivers, although often with unclear results. To study the effects of habitat limitations on the common barbel (Barbus barbus), a riverine litophilic cyprinid fish, an age-structured population model was developed. Using a Bayesian modeling approach, spawning and fry (0+ juvenile) habitat availability was integrated in the model in a spatially explicit way. Using Beverton-Holt and Ricker recruitment models, density dependence was incorporated in the spawning process and the recruitment of 0+ juveniles. Model parameters and their uncertainty ranges were obtained from reviewing the existing literature. The uncertainty of the processes was intrinsically accounted for by the inherently probabilistic nature of the Bayesian model. By testing various scenarios of habitat availabilities for the barbel, we hypothesize that improvement of the fish stock will be reached only at a well specified ratio of spawning to fry habitat. Model simulations revealed substantial abundance improvements at rather equal amounts of about 10% cover of both habitats, while even substantial improvements of either spawning or fry habitats only will result in little or no increase of abundance. Higher ratios of spawning to fry habitat were found to lower population recovery times. This work provides a tool that serves the assessment and comparison of river restoration scenarios as well as benchmarking rehabilitation targets in the planning phase. When targeting restoration of fish stocks, focusing only on one key life stage or process (such as spawning), without considering potential bottlenecks in other stages, can result in little to no improvement.

We analyse recent morphological evolution of braiding rivers of disparate regions of the Earth to develop and address the hypothesis that braiding of rivers tends to be reduced by human presence and related activities. Firstly, through a large-scale literature survey we observe generalised paths of bed degradation, channel narrowing and shift towards single-thread configuration in braided reaches due to multiple anthropogenic stressors. Secondly, we select three rivers from different geographic contexts characterised by complementary anthropic stressors for a detailed analysis (the lower Waitaki River in New Zealand, the middle Piave River in Italy and the lower Dunajec River in Poland) which shows that these rivers have undergone very similar trajectories of morphological change. In previous works, these morphodynamic changes have been related to the alteration of the fundamental physical processes of braided rivers, due to anthropogenic changes in constraints and controls. Here, a closer analysis of these alterations shows that analogous morphological evolutionary trajectories can result from very different paths of causation, i.e., from different management causes and different alteration of physical processes. Through the use of pattern predictors we analyse observed morphological trajectories and potential for recovery. We highlight the role of different geographic contexts as sources of constraints and drivers to the river evolution, with reference both to the physical and human environment, showing that the observed similar trajectories are the product of different local conditions and characteristics. These observations have implications for river management and restorations.

The presence of lateral planimetric constraints preventing free migration and avulsion has a significant influence on the planform dynamics of river meanders. This particular confined kind of meandering rivers is definitely understudied, especially in comparison to freely migrating ones. Through a semi-analytical meander model, here we attempt to investigate the effect of the confined floodplain width through a morphodynamic modeling approach. The confined floodplain width is defined as the width between symmetric lateral confinement where the river is free to migrate, on the planform pattern and dynamics. Model results illustrate that weak confinement (i.e. loose floodplain boundaries) increases planform irregularity, with the river centerline preferentially lying close to floodplain boundaries, while strong confinement (tight floodplain boundaries) leads to a remarkable planform regularity, constituted by periodic sequences of sawtooth-shaped meanders. Bend orientation is reminiscent of the sub/super-resonant regime regardless of the confinement width. Model results are supported by good agreement with available field and remote sensing observation on selected case studies of confined meandering rivers in Canada previously studied by Nicoll and Hickin (2014).

Amongst different climatic and anthropogenic drivers, water resources management can cause massive changes to the natural regime of a lake after its regulation, thereby affecting the quantity and quality of water intended for satisfying the multiple basin water requirements. Here, we investigate the multi-decadal variation of the water levels and outflows of Lake Garda, the largest in Italy, where the dam operational rules and the related basin water needs heavily altered the annual and seasonal trend of the lake regime since its regulation in 1951. Daily lake levels and outflows were first collected and digitized for the period 1888–2020, thus providing a unique database of 133 years that allowed a consistent comparison between natural and regulated periods. Statistical analyses highlighted a significant change of the inter-annual trend of the lake outflows, which passed from upward to downward after regulation, against a constant increasing trend of the water levels. Conversely, water levels showed a more remarkable shifts on a seasonal scale if compared to the outflows, revealing the influence of summer and winter basin water needs. Additional analyses on the inter-annual variation of the main downstream water demands regulated by the dam, i.e. the irrigation, hydropower and fluvial ecosystem requirements, outlined their relevance in changing the lake regime, influencing dam operational policies, which progressively limited the share of water released for ecosystem integrity. A comparison between the lake levels and outflows recorded for the pre-regulation and post-regulation periods of some selected European perialpine lakes finally highlighted different effects on the lake regime, drawing attention to the importance of defining the role of the dam operational policies within the current scenario of climate change and changing water demands.

Within the past 30 years there have been two major heatwave events (in 2003 and 2006) that broke 500-year-old temperature records in Europe. Owing to the growing concern of rising temperatures, we analyzed the potential response in a number of river sections that are subject to hydropeaking and thermopeaking through the intermittent release of water from hydropower stations. Thermopeaking in alpine streams is known to intermittently cool down the river water in summer and to warm it up in winter. We analyzed the response of river water temperature to air temperature during heatwaves at 19 gauging stations across Switzerland, using a 30-yr dataset at a 10-min resolution. Stations were either classified into “unpeaked” or “peaked” groups according to four statistical indicators related to hydropeaking and thermopeaking pressure. Peaked stations were exposed to reduced temporal variability in river water temperature, and it was determined that correlations between river water and air temperature were weaker for peaked stations compared with unpeaked stations. Similarly, peaked stations showed a much weaker response to heatwaves compared with unpeaked stations. It is important to note that this “cooling effect” created by hydro-thermopeaking was most pronounced during the two major heatwave events that took place in 2003 and 2006. Furthermore, results from thermal stress events on the growth of a typical cold eurythermic fish species (brown trout) increased continuously in rivers subject to peaked station water release during heatwaves. While hydropower operations that take place high up on mountains releasing hypolimnetic water may mitigate the adverse effects of heatwaves on downstream alpine river ecosystems locally, our results show the complexity of an artificial physical template associated with flow regime regulation in alpine streams.

et al., Higher Education Institutions play a critical role in societies transition towards sustainable development, educating future professionals and decision makers. In the last few decades, a number of technical universities have devoted major efforts to integrating sustainable development into engineering curricula. There is still, however, an increasing need to further transform learning and training environments and build capacity of educators and trainers on sustainable development issues. Against this background, this paper assesses the role of online training courses, within continuing professional development strategies, in promoting sustainable human development in engineering degrees. It was built upon the implementation of a European initiative, the Global Dimension in Engineering Education, promoted by a transdisciplinary consortium of technical universities and non-governmental organisations. In terms of method, this study analyses two sets of quantitative and qualitative indicators to assess i) the perceived quality/relevance of the training proposals, and ii) the learning acquisition of participants. Quantitative indicators were complemented by a descriptive analysis of findings from a semi-structured survey. The results provide evidence that online learning can be an effective approach for continuing professional development of academics. The findings also suggest that participants perceived online courses’ contents and curricula, developed jointly by academics and practitioners of non-governmental organisations, as relevant and useful for integrating sustainability principles in teaching activities. To conclude, authors recommend the leaders of higher educational institutions to explore the integration of online courses addressed to faculty into university policy and strategies, as a way to promote professional development and the engagement of academics on sustainable development., The research was conducted in the framework of the European initiative Global Dimension in Engineering Education financed by: - European Commission, Non-State Actors and Local Authorities in Development, Raising public awareness of development issues and promoting development education in the European Union Reference: EuropeAid/131141/C/ACT/MULTI, Number of proposal: DCI-NSAED/2012/280-929. - Barcelona City Council, Program: Barcelona Solidaria 2013. Grant number: 13ED0046.

To date, the role of riparian trees in the formation of scroll bars, ridges and swales during the evolution of meandering channels has been inferred largely from field observations with support from air photographs. In situ field observations are usually limited to relatively short periods of time, whereas the evolution of these morphological features may take decades. By combining field observations of inner bank morphology and overlying riparian woodland structure with a detailed historical analysis of airborne LiDAR data, panchromatic and color images, we reconstruct the spatial and temporal evolution of the morphology and vegetation across four meander bends of the Tagliamento River, Italy. Specifically we reveal (i) the appearance of deposited trees and elongated vegetated patches on the inner bank of meander bends following flood events; (ii) temporal progression from deposited trees, through small to larger elongated vegetated patches (pioneer islands), to their coalescence into long, linear vegetated features that eventually become absorbed into the continuous vegetation cover of the riparian forest; and (iii) a spatial correspondence between the resulting scrolls and ridge and swale topography, and tree cover development and persistence. We provide a conceptual model of the mechanisms by which vegetation can contribute to the formation of sequence of ridges and swales on the convex bank of meander bends. We discuss how these insights into the biomorphological processes that control meander bends advance can inform modelling activities that aim to describe the lateral and vertical accretion of the floodplain during the evolution of vegetated river meanders.

The provision of important river ecosystem services (ES) is dependent on the flow regime. This requires methods to assess the impacts on ES caused by interventions on rivers that affect flow regime, such as water abstractions. This study proposes a method to i) quantify the provision of a set of river ES, ii) simulate the effects of water abstraction alternatives that differ in location and abstracted flow, and iii) assess the impact of water abstraction alternatives on the selected ES. The method is based on river modelling science, and integrates spatially distributed hydrological, hydraulic and habitat models at different spatial and temporal scales. The method is applied to the hydropeaked upper Noce River (Northern Italy), which is regulated by hydropower operations. We selected locally relevant river ES: habitat suitability for the adult marble trout, white-water rafting suitability, hydroelectricity production from run-of-river (RoR) plants. Our results quantify the seasonality of river ES response variables and their intrinsic non-linearity, which explains why the same abstracted flow can produce different effects on trout habitat and rafting suitability depending on the morphology of the abstracted reach. An economic valuation of the examined river ES suggests that incomes from RoR hydropower plants are of comparable magnitude to touristic revenue losses related to the decrease in rafting suitability.

We report on a multi-decadal analysis of alternate bar dynamics in a 41.7 km reach of the Alpine Rhine River, which represents an almost unique example of a regulated river with fixed levees, straight reaches and regular bends in which alternate gravel bars spontaneously formed and migrated for more than a century. The analysis is based on freely available Landsat imagery, which provided an accurate and frequent survey of the dynamics of the alternate bar configuration since 1984. Bars were characterized in terms of wavelength, migration, and height. Longitudinal and temporal patterns are investigated as a function of flood occurrence and magnitude and in relation to the presence of local planform discontinuities (bends and ramps) that may affect their dynamics. Bars in the upper part of the reach are mostly steady and relatively long (about 13 channel widths); bars in the lower part of the reach are migrating and shorter (about 9 channel widths). Bar height is rather uniform along the reach, ranging between 3 to 4 m. The temporally long hydrological dataset allowed the investigation of bar migration during flood events, showing that bars migrate faster for intermediate floods. The observed relationship between bar migration and wavelength was consistent with linear theories for free migrating and steady forced bars in straight channels. The comparison of theories with observations highlights the key role of theories to support interpretation of observations, for a better understanding of the morphodynamic processes controlling bar formation and dynamics. This article is protected by copyright. All rights reserved.

We propose a bio-morphodynamic model at bend cross-sectional scale for the lateral migration of river meander bends, where the two banks can migrate separately as a result of the mutual interaction between river flow, sediments and riparian vegetation, particularly at the interface between the permanently wet channel and the advancing floodplain. The model combines a non-linear analytical model for the morphodynamic evolution of the channel bed, a quasi-1D model to account for flow unsteadiness, and an ecological model describing riparian vegetation dynamics. Simplified closures are included to estimate the feedbacks among vegetation, hydrodynamics and sediment transport, which affect the morphology of the river-floodplain system. Model tests reveal the fundamental role of riparian plants in generating bio-morphological patterns at the advancing floodplain margin. Importantly, they provide insight into the biophysical controls of the ‘bar push’ mechanism and into its role in the lateral migration of meander bends and in the temporal variations of the active channel width.

River research often addresses the influence of anthropogenic and natural processes on the ecological, hydrological, and geomorphological dynamics of river systems. However, here we take a river-centered approach and consider how rivers influence their landscapes by developing concepts of river landscape ‘signatures’ and ‘envelopes.’ The influence of a river penetrates well beyond its channel into the atmosphere, across the land surface, and into the subsurface. We define a signature as an emergent property of a set of processes acting on a river landscape, and its envelope as the dynamic penetration of the signature across the landscape. The potential to recognize river signatures and envelopes is driven by unprecedented expansion in data acquisition, processing, and modeling technologies. The spatial envelope of any particular signature will have fuzzy and temporally dynamic edges, may rapidly expand and contract, may differ in its extent from other signatures, and may be highly permeable to many organisms using the river (and broader) landscape. However, an understanding of the approximate dynamic envelope of a signature is crucial to understanding the contribution of rivers at a landscape scale and to informing the sustainable management of these landscapes and their ecosystem services. WIREs Water 2016, 3:313–325. doi: 10.1002/wat2.1143 For further resources related to this article, please visit the WIREs website.

The applicability of a portable, commercially available surface velocity radar (SVR) for noncontact stream gauging was evaluated through a series of field-scale experiments carried out in a variety of sites and deployment conditions. Comparisons with various concurrent techniques showed acceptable agreement with velocity profiles, with larger uncertainties close to the banks. In addition to discharge error sources shared with intrusive velocity-area techniques, SVR discharge estimates are affected by flood-induced changes in the bed profile and by the selection of a depth-averaged to surface velocity ratio, or velocity coefficient (α). Cross-sectional averaged velocity coefficients showed smaller fluctuations and closer agreement with theoretical values than those computed on individual verticals, especially in channels with high relative roughness. Our findings confirm that α = 0.85 is a valid default value, with a preferred site-specific calibration to avoid underestimation of discharge in very smooth channels (relative roughness ∼ 0.001) and overestimation in very rough channels (relative roughness > 0.05). Theoretically derived and site-calibrated values of α also give accurate SVR-based discharge estimates (within 10%) for low and intermediate roughness flows (relative roughness 0.001 to 0.05). Moreover, discharge uncertainty does not exceed 10% even for a limited number of SVR positions along the cross section (particularly advantageous to gauge unsteady flood flows and very large floods), thereby extending the range of validity of rating curves.

Meanders are oscillatory systems characterized with multiple spatial frequencies in their planforms. Although the concept of dominant meander wavelength (DMW) is central to morphodynamic research on river meandering, shorter and longer spatial scales of oscillations are also relevant. Using Continuous Wavelet Transform (CWT), we present an objective quantitative characterization of the relevant wavelengths of meandering rivers. Analysis of synthetic meanders generated through Kinoshita curves and real meandering rivers show that DMW can be better detected by applying CWT to the spatial series of the direction-angle, instead of curvature, because the latter shifts the meander oscillation energy toward shorter harmonics. This is related to the typical observed high ratio of meander arclength to channel width, as emerging from field observations and from morphodynamic modeling of meanders, implying the dimensionless wavenumber of meander oscillations to be an O 10 − 1 number. The capability of CWT of capturing local as well as global information in a spatial series is exploited by analyzing two CWT-based indicators, which express the relevance of other wavelengths with respect to the local DMW within the same reach ( M λ ) and the variability of the local DMW with respect to the global DMW ( S λ ). Thresholding the M λ indicator shows that the global DMW corresponds to local DMW for only the most regular meanders. At longer scales, the S λ indicator also reveals the existence of spatial modulations of the direction-angle oscillations in real meandering rivers, which have been previously detected only in synthetic planforms generated by morphodynamic models. This correspondence between observations and modeling indicates the potential of CWT analysis of meanders to provide further insight into the connections between the form and processes of channel meandering, as it suggests that spatial modulations might be inherent in meander-planform dynamics and related to the tendency of meanders to evolve in wavegroups, a potential cause of the so called ‘cutoff avalanches’ observed in natural and modeled meandering streams.

The thermal regime of rivers is threatened by anthropogenic stresses at a large variety of timescales. We focus on sub-daily thermal alterations induced by the release of hypolimnetic water for hydropower production (thermopeaking). We analyse the thermal signal focusing on the following characteristics that are potentially affected by hypolimnetic releases: (i) sub-daily thermal rate of change and (ii) oscillation frequencies contained in the thermal signal. Through a proper scaling, we derive two dimensionless at-a-station indicators to compare alterations among stations with different locations and physiographic characteristics of the basins. Then we analyse the data from two different thermal datasets (Italy/Switzerland) for a total of 48 stations with 10 min time resolution of temperature data. The stations are grouped according to the absence of upstream hydropeaking releases (29 stations, reference group) and the existence of upstream hydropeaking, hence potentially impacted by thermopeaking (19 stations, altered group). Using a simple statistical approach, based on a non-parametric definition of outliers, we identify the range of variability of the two indicators for the reference, unaltered group. This range measures the ‘natural’ sub-daily thermal variability of the proposed indicators. Finally, we investigate the seasonality effects on the two proposed indicators and it results, that sub-daily alterations mostly occur during summer. The two indicators represent a novel tool for the assessment of river thermal regime alterations and can be easily included in existing methodologies to assess river quality.

We assessed the effects of repeated hydropeaking over five consecutive days on the zoobenthic community by manipulating discharge in five experimental flumes directly fed by an Alpine stream. Treatment consisted of two different hydropeaking intensities which increased discharge two- and threefold from baseflow and lasted for 5 h each day. The resulting sudden changes in flow directly affected benthic invertebrates through the induction of catastrophic drift as a direct response to high (hydropeaking) flow conditions, and of behavioural drift in the low, baseflow conditions (at the conclusion of each hydropeaking event) for some taxa. We observed: an initial strong peak in catastrophic drift within the first 3 min of increased discharge, followed by a decreased drift rate throughout the following hours of the experiment; a strong response in the first day of the simulation, with successive days having substantially decreased drift; taxa-specific responses over the short and long-time scales: least-resistant taxa (i.e. Baetis spp.) were removed via the initial catastrophic drift, while more resistant taxa began to behaviourally drift later in each hydropeak (i.e. Simuliidae). Peaks in drift rates corresponded to the initial removal of CPOM which, during low flows, provided habitat and food resource for a high number of individuals and taxa. Quantification of drift responses over time scales larger than the single hydropeaking event underlines the relevance of the typical intermittency and repetition frequency as a stress factor for benthic communities, and that the response to hydropeaking is closely related to the time elapsed since the last perturbation. Copyright © 2015 John Wiley & Sons, Ltd.

In this paper we propose a new theoretical model to investigate the influence of temporal changes in channel width on river bar stability. This is achieved by performing a nonlinear stability analysis, which includes temporal width variations as a small-amplitude perturbation of the basic flow. In order to quantify width variability, channel width is related with the instantaneous discharge using existing empirical formulae proposed for channels with cohesionless banks. Therefore, width can vary (increase and/or decrease) either because it adapts to the temporally varying discharge or, if discharge is constant, through a relaxation relation describing widening of an initially overnarrow channel towards the equilibrium width. Unsteadiness related with changes in channel width is found to directly affect the instantaneous bar growth rate, depending on the conditions under which the widening process occurs. The governing mathematical system is solved by means of a two-parameters (ε, δ) perturbation expansion, where ε is related to bar amplitude and δ to the temporal width variability. In general width unsteadiness is predicted to play a destabilizing role on free bar stability, namely during the peak stage of a flood event in a laterally unconfined channel and invariably for overnarrow channels fed with steady discharge. In this latter case, width unsteadiness tends to shorten the most unstable bar wavelength compared to the case with constant width, in qualitative agreement with existing experimental observations.

We study the numerical approximation of the two-dimensional morphodynamic model governed by the shallow water and Exner equations to simulate reach-scale two-dimensional morphodynamics of bedload-dominated alluvial rivers. The solution strategy relies on a full coupling of the governing equations within each time step. The resulting system of governing equations contains nonconservative products related to the longitudinal and lateral bed slopes and source terms related to friction. The full problem is solved numerically on unstructured triangular grids, simultaneously updating the principal part and adding the source terms (friction) using a splitting technique. The principal part is solved by means of a novel second-order accurate upwind-biased centred scheme of the finite volume type, while the source terms are added to the problem by solving a system of ordinary differential equations. A new algorithm for treating the wetting-and-drying is also proposed. The model is applied to well-established test problems in order to verify the accuracy of the proposed method, the robustness of the wetting-and-drying algorithm and the ability of the model in dealing with transcritical flows. Finally we test the model ability to reproduce two dimensional morphodynamic processes occurring at the scale of tens of channel widths in bedload dominated alluvial rivers with homogeneous grain size. This is achieved by comparing model outcomes with those of analytical theories and flume experiments on the same morphodynamic processes. These selected “benchmarks” include migrating free bars spontaneously developing in straight reaches, steady bars forced by abrupt river planform changes and the dynamics of channel bifurcations.

Cultural and recreational river ecosystem services and their relations with the flow regime are still poorly investigated. We develop a modelling-based approach to assess recreational flow requirements and the spatially distributed river suitability for white-water rafting, a typical service offered by mountain streams, with potential conflicts of interest with hydropower regulation. The approach is based on the principles of habitat suitability modelling using water depth as the main attribute, with preference curves defined through interviews with local rafting guides. The methodology allows to compute streamflow thresholds for conditions of suitability and optimality of a river reach in relation to rafting. Rafting suitability response to past, present and future flow management scenarios can be predicted on the basis of a hydrological model, which is incorporated in the methodology and is able to account for anthropic effects. Rafting suitability is expressed through a novel metric, the "Rafting hydro-suitability index" (RHSI) which quantifies the cumulative duration of suitable and optimal conditions for rafting. The approach is applied on the Noce River (NE Italy), an Alpine River regulated by hydropower production and affected by hydropeaking, which influences suitability at a sub-daily scale. A dedicated algorithm is developed within the hydrological model to resemble hydropeaking conditions with daily flow data. In the Noce River, peak flows associated with hydropeaking support rafting activities in late summer, highlighting the dual nature of hydropeaking in regulated rivers. Rafting suitability is slightly reduced under present, hydropower-regulated flow conditions compared to an idealized flow regime characterised by no water abstractions. Localized water abstractions for small, run-of-the-river hydropower plants are predicted to negatively affect rafting suitability. The proposed methodology can be extended to support decision making for flow management in hydropower regulated streams, as it has the potential to quantify the response of different ecosystem services to flow regulation.

Meandering channels is a vast research field, spanning a broad variety of time and space scales, environmental domains, and conceptual and methodological approaches. This paper serves as an introduction to this special issue of Geomorphology “Meandering Channels”, which addresses the need for sustained scientific dialogue on the dynamics of meandering channels. In an effort to place this issue in the broad context of this rapidly changing and advancing research field, we begin by discussing the motivation behind this issue. Then, we continue by summarizing the main novel research contributions of each paper. Finally, we conclude by proposing five major research directions that directly develop from the ensemble of the scientific contributions to this special issue. These research directions emphasize the critical importance of the coupling of near-bank geomorphic and flow processes; the characterization of co-evolution of meandering rivers and their floodplains; the need to improve linkages between meandering rivers research and river management and restoration; the potential of expanding laboratory-based research; and the integration of holistic and reductionist approaches.

The present work revisits the classical, uniform-width bend theory with the aim to understand whether and how spatial width oscillations can affect the process of linear bend stability that initiates meander planform evolution. Although longitudinal oscillations of channel width are common along many meandering streams, little investigation of their properties and dynamic effects has been pursued so far. The theory therefore accounts for width variations as a geometrical forcing in a depth-averaged model of meander morphodynamics by assuming the potential interaction with the classical curvature forcing effect. A first quantification of width variations is made by referring to a freely evolving meandering river, which shows that the dimensionless amplitude of width variations is a ‘small’ parameter with comparable magnitude to that of curvature variations, thus suggesting the use of a two-parameter perturbation expansion. Moreover, it is reasonable to assume that channel width oscillates in space with a double frequency relative to curvature, which implies that one nonlinear interaction between the two forcing effects is enough to reproduce the effect of spatial width variations on the process of bend stability. Overall, width variations consistently promote the instability of shorter bends with respect to meanders with uniform width: on average, this predicted tendency is supported by analysis of field data referring to hundreds of natural meander bends. The effect on meander wavelength selection depends on the location of the widest section relative to the bend apex. Under typical formative conditions of gravel-bed rivers, with large-enough channel aspect ratios, two distinct most unstable longitudinal modes develop. Such behaviour is absent when the width is uniform, and suggests a mechanistic interpretation for the reach-scale occurrence of chute cutoffs that can be observed more frequently in wider-at-bends than in equiwidth meandering channels.

The extent and pattern of width variations along a meandering channel and its association with variation in bed topography and development of mid-channel bars have been examined through field survey evidence for a reach of the River Bollin in NW England. The wet width has been quantified along the reach by applying a hydraulic model to surveyed cross sections under a range of discharges between low flow and defined bankfull conditions. This approach allows an objective, modelling-based method to compute channel width. The high spatial resolution of the topographical survey allows capture of significant variations in the cross-sectional morphology at the meander wavelength scale. Results disclose some features of longitudinal and stage-dependent width variability in meanders. Width variation is shown to be highly correlated with curvature: at bankfull conditions width peaks in bend apex sections exceed those at inflection sections and can be up to twice greater. The width-curvature behavior is correlated with the pattern of bed and banks morphology, which is different in bend apices and in meander inflections. The survey shows that the bedform morphology can be characterized by a mid-channel bar pattern that is initiated at the inflection section and that the bedform dynamics can be closely associated with channel width variations.

The ‘Global Dimension in Engineering Education’ (GDEE) network is an initiative that aims to increase the awareness, critical understanding and attitudinal values of undergraduates and postgraduates students in technical universities across Europe related to Sustainable Human Development (SHD) and its relationship with technology. This is being dealt with by integrating SHD as a cross-cutting issue in teaching activities by improving the competences of academics and through engaging both staff and students in initiatives related to SHD. The GDEE started as a collaborative project between a consortium of European Universities and NGOs. The chapter presents a common understanding of how best to establish effective education for global development, and presents a pedagogical approach to facilitate the connection between theoretical knowledge (lecturers and students from universities) with practice (through NGOs). It discusses this approach through the analysis of case studies of best practice from those already working in this area within higher education across Europe. It concludes with the presentation of a continued professional development (CPD) approach for academics that uses a series of online training courses, with support from a series of contextual case studies written by NGOs to support teaching human development within engineering courses., European Commission, Non-State Actors and Local Authorities in Development, Raising public awareness of development issues and promoting development education in the European Union Reference: EuropeAid/131141/C/ACT/MULTI, Number of proposal: DCI-NSAED/2011/63, Barcelona City Council, Team GDEE.

The recent (25 years) morphodynamics of a proglacial reach of the Ridanna Creek, North-East Italy, evolving in the absence of human constraints, has been investigated by means of an intensive field activity and of the analysis of aerial photographs. The study reach mostly displays a braided morphology, with sharp downstream variations of valley gradient, sediment size and formative conditions within the main channel. These discontinuities are associated with different processes of channel adjustment at different timescales, which have been quantified by coupling hydrological with morphological information. Several processes of channel change and variations in braiding intensity have been documented along the whole reach and highlight how a regular, weakly meandering main channel may significantly affect the morphodynamics of the braided network. A first attempt to predict the morphological instability of this main channel at the observed spatial scales through existing linear theories of curved river channels shows a good agreement with field observations. Finally, the complete hydro-morphodynamical characterization of such an undisturbed alpine river reach can provide a relevant contribution to the definition of reference conditions for Alpine rivers required by the EU Water Framework Directive. Copyright © 2007 John Wiley & Sons, Ltd.