With the increasing availability of big geospatial data (e.g., multi-spectral satellite imagery) and access to platforms that support multi-temporal analyses (e.g., cloud-based computing, Geographical Information Systems, GIS), the use of remotely sensed information for monitoring riverine hydro-morpho-biodynamics is growing. Opportunities to map, quantify and detect changes in the wider riverscape (i.e., water, sediment and vegetation) at an unprecedented spatiotemporal resolution can support flood risk and river management applications. Focusing on a reach of the Po River (Italy), satellite imagery from Landsat 5, 7, and 8 for the period 1988–2018 were analyzed in Google Earth Engine (GEE) to investigate changes in river planform morphology and vegetation dynamics associated with transient hydrology. An improved understanding of these correlations can help in managing sediment transport and riparian vegetation to reduce flood risk, where biogeomorphic processes are commonly overlooked in flood risk mapping. In the study, two established indices were analyzed: the Modified Normalized Difference Water Index (MNDWI) for monitoring changes in the wetted river planform morphology, inferring information about sediment dynamics, and the Normalized Difference Vegetation Index (NDVI) for evaluating changes in vegetation coverage. Results suggest that planform changes are highly localized with most parts of the reach remaining stable. Using the wetted channel occurrence as a measure of planform stability, almost two-thirds of the wetted channel extent (total area = 86.4 km²) had an occurrence frequency >90% (indicating stability). A loss of planform complexity coincided with the position of former secondary channels, or zones where the active river channel had narrowed. Time series analysis of vegetation dynamics showed that NDVI maxima were recorded in May/June and coincided with the first peak in the hydrological regime (occurring in late spring and associated with snowmelt). Seasonal variation in vegetation coverage is potentially important for local hydrodynamics, influencing flood risk. We suggest that remotely sensed information can provide river scientists with new insights to support the management of highly anthropized watercourses.

An 8-km-long and 250-m-wide reach of the Po River (Italy) was surveyed with two vessels, aiming to investigate the channel morphology and flow field characterizing this major Italian river and to provide data for the calibration of a numerical model. The first vessel was equipped with a multibeam ecosounder (MBES), whereas an acoustic doppler current profiler (ADCP) was located on the second one. Fixed-vessel ADCP measurements were used to preliminarily investigate the turbulence variability affecting the reliability of moving-vessel measurements. To evaluate the friction velocity by using moving-vessel measurements, the vertical variance of velocity profiles as an alternative to logarithmic fitting of ADCP profiles was estimated. An average of 30-m cells of depth-averaged velocity, friction velocity, and surface-bottom velocity angle are presented in maps as the most relevant flow field features. The flow field and channel morphology at bed-form or channel scales showed noticeable correlations (0.9). In ...

The use of echo-levels from Acoustic Doppler Current Profiler (ADCP) recordings has become more and more common for estimating suspended bed-material and wash loads in rivers over the last decade. Empirical, semi-empirical and physical-based acoustic methods have been applied in different case studies, which provided relationships between scattering particles features derived from samples (i.e., concentration and grain size) and corresponding backscattering strength and sound attenuation. These methods entail different assumptions regarding sediment heterogeneity in the ensonified volume (e.g., particle size distribution (PSD) and spatial concentration gradient). Our work was to compare acoustic backscatter and attenuation properties of suspended sediments, sampled in the rivers Parana and Danube that represented rather different hydro-sedimentological conditions during the surveys. The Parana represents a large sandy river, characterized through a huge watershed and the typical bimodal PSD of sediment in suspension, while the Danube represents in the investigated reach an exposed sand-gravel bed and clay-silt particles transported in the water column in suspension. Sand and clay-silt concentrations clearly dominate the analyzed backscattering strength in the rivers Parana and Danube, respectively, with an effect of PSD level of sorting in the latter case. This comparison clarifies the extent of assumptions made, eventually advising on the actual possibility of applying certain ADCP methods, depending on the expected concentration gradients and PSD of suspended sediment to be investigated.

River systems evolve in response to the construction of dams and artificial reservoirs, offering the possibility to investigate the short-term effects of base level oscillations on fluvial architecture. A major effort has been dedicated to the understanding of river response downstream of large dams, where deep channel incisions occur in response to the removal of sediment that is sequestered in the upstream reservoir. Integrating field observations and numerical-modeling results, this work quantifies the sedimentary and morphological changes of the Po River (Italy) upstream of the Isola Serafini dam to investigate the impact of dam-induced backwater on river morphodynamics. The construction of a reservoir generates a new base level that forces an upstream shift of alluvial lithofacies and a change in the planform geometry of the river. The lateral migration rate of the channel is up to 45 m/yr upstream of the influence of backwater flow and ca. 10 m/yr at the transition from normal to backwater flow conditions (30 km from the dam). Within this reach, a reduction of the bed shear stress promotes deposition of coarse-grained sediment and the emergence of the gravel–sand transition of the river. The lateral migration of the channel continuously decreases over time, and rates < 5 m/yr can be observed in the reservoir backwater zone. This trend is accompanied by the drowning of channel bars, the reduction of river competence, and an increase in bedform spacing. Oscillatory backwater and drawdown surface water profiles can be observed closer to the dam, which are associated with varying low-discharge and high-discharge events, respectively. While low-flow conditions, persisting for much of the year, allow the deposition of fine-grained sediment, high-discharge events promote not only the resuspension and transport of fine material but also the progressive erosion of channel bars and the overall deepening of the thalweg. This study provides a clear picture of the river evolution in response to the construction of a hydropower dam that may be of help in predicting how other fluvial systems will respond to future human interventions. Moreover, the result of how changes in base level and oscillations in water surface profile (backwater and drawdown) control river hydro-morphodynamics and sediment transport may provide new insights when reconstructing ancient fluvial and deltaic sequences.