Earth Surface Processes and Landforms最新文献

The origin of the Amazon River is formed at the confluence of the Marañón and Ucayali rivers. Remote sensing and detailed hydrodynamics, sediment transport and bed morphology analysis under different hydrological conditions have been applied to understand the control mechanisms of the modern confluence, thus informing about ancient confluences. Results showed that: 1) meandering-meandering confluences existed when bifurcated meandering channels from the Marañón River joined the meandering Ucayali River, 2) far-field scale provided the boundary conditions for the near-field scale processes. In the case of the Marañón River, the spatial frequency and displacement of incoming anabranching structures to the confluence location set the boundary conditions for the near-field scale. In the case of the Ucayali River, the incoming hydrodynamics and bed morphology are governed by far-field processes such as the occurrence of cutoffs, 3) high intensity secondary flows at large rivers were observed at far- and near-field scales, where previous studies have reported that secondary flows are weak or nonexistence or mainly found downstream of confluences. Finally, 4) even though the Marañón River is larger compared with the Ucayali River, the confluence hydrogeomorphology is governed by the Ucayali River because of more developed and stronger secondary flows.

In a recently published report focused on the role of swelling of Triassic clays as the dominant process that led to the local steepening of competent Jurassic strata, its authors presented an opinion on the lack of evidence for the existence of the Gnieździska–Brzeziny strike-slip fault along the contact between the Triassic and Jurassic rocks. This discussion presents the structural, geophysical, cartographic and geomechanical data indicating that the contact of Triassic and Jurassic rocks is defined by the vertical dextral strike-slip Gnieździska–Brzeziny fault, which was formed after tilting of the beds in the Late Cretaceous. The presented evidence validates the tectonic deformation of Mesozoic rocks related to strike-slip faulting. The dominant horizontal contraction across the fault planes within the restraining stepovers resulted in tilting of the beds, which is a well-recognized phenomenon within the strike-slip fault networks worldwide.

Understanding the effects of human disturbance on the bedload transport regime of anthropised rivers is a topic of growing importance, as such information is of interest for adequate river diagnosis, correct implementation of restoration measures and appropriate design of post-action monitoring programs. However, such assessments are complex, especially in sites where multiple factors simultaneously influence the bedload transport regime, so that it is difficult to establish simple causal relationships between human disturbances and changes in the sediment transport regime, notably on bedload. To overcome this, there is a need for rigorous hypothesis-driven approaches to assess the isolated effects of each driver. With this in mind, we have characterised the dynamics of bedload transport in the Upper Garonne (Central Pyrenees, Spain-France), a river impacted by sediment retention, flow diversion and mining that influence its morphological conditions and transport regime. We assessed the effects of (1) surface grain size distribution, (2) river morphology, (3) sediment supply and (4) flow diversion on the bedload transport regime. Four sites with different degrees of river anthropisation were selected. After defining hypotheses on the most likely bedload transport conditions for each site, we proposed a set of discriminating criteria to test these hypotheses, based on temporal within-site and spatial between-site comparisons of coarse particle tracking measurements over four years. The results of this research showed that the hydrosedimentary regime of the Garonne is controlled by a complex combination of drivers such as valley physiography, which exerts a first-order control on differences in reach-scale bedforms and bedload dynamics; and human disturbances which contribute to a reduction in sediment supply through changes in land cover and hydropower dams, or to changes in hydrology (i.e., flow competence) due to water diversion and abstraction.

Estuarine tidal channels are active geomorphic units in tidal flats. However, accurate information on the spatiotemporal changes in tidal channel systems remains scarce. The width of the tidal channels may vary from several kilometres to tens of centimetres. Monitoring tidal channel evolution is complicated because of periodic tidal scouring, anthropogenic activities and sea level rise. In this study, we propose a synergetic classification method to detect and extract morphological information of estuarine tidal channels with a spatial resolution of up to 3 m by fusing PlanetScope multispectral data with C-band GaoFen-3 fully polarised Synthetic Aperture Radar (SAR) data and machine learning algorithms. Considering the Yellow River Estuary as an example, the spectral features, vegetation and water index, polarisation and texture features derived from the multispectral and SAR images were selected as input data for classifiers according to feature importance ranking. Comparison to the maximum likelihood, and support vector machine classifiers, the synergetic classification with random forest showed the best performance, with an overall accuracy of 99.6%. Based on these results, the total number of tidal channels in the Yellow River Estuary reached 872, with a total length of 348.8 km. The spatiotemporal changes in the central axis over the last 4 years (2019–2022) suggest that the evolution of tidal channels was mainly controlled by ocean dynamics and anthropogenic activities. This method provides a cost-effective alternative to accurately map tidal channel systems in global estuarine and coastal zones and helps to quantitatively describe their morphological evolution, stability and drivers.