More than 50 years ’ river training practices in the Lower Yellow River provide valuable experience in river management for flood control in rivers having rapid flow changes, silting beds, and active channel migrations and are of importance in understanding the fluvial processes in regulated rivers with high sediment loads. Planned channel alignments for river training in the Lower Yellow River usually consist of a series of consecutive moderate bends representing the natural tendency of flows. Flow guide works, namely spur dikes, were constructed on the concave banks of the planned bends to protect the channel against scouring and migration by deflecting the current away from bends and further guiding the main flow from one bend to the next one. As a result, well-planned flow guide works can play a crucial role in limiting channel shifting and migration and in establishing a relatively stable channel. Enough flow guide works, on both sides together reaching about 80% of the channel length, may change the...

We analyze why the sediment discharges of fine-grained rivers are an order of magnitude larger than predicted by current theory.

Water is essential for the survival of plants, animals, and human beings. It is imperative to effectively manage and protect aquatic resources to sustain life on Earth. Small tributaries are an important water resource originating in mountain areas, they play an important role in river network evolution and water transmission and distribution. Snow and cloud cover cast shadows leading to misclassification in optical remote sensing images, especially in high-mountain regions. In this study, we effectively extract small and open-surface river information in the Upper Yellow River by fusing Sentinel-2 with 10 m resolution optical imagery corresponding to average discharge of the summer flood season and the 90 m digital elevation model (DEM) data. To effectively minimize the impact of the underlying surface, the study area was divided into five sub-regions according to underlying surface, terrain, and altitude features. We minimize the effects of cloud, snow, and shadow cover on the extracted river surface via a modified normalized difference water index (MNDWI), revised normalized difference water index (RNDWI), automated water extraction index (AWEI), and Otsu threshold method. Water index calculations and water element extractions are operated on the Google Earth Engine (GEE) platform. The river network vectors derived from the DEM data are used as constraints to minimize background noise in the extraction results. The accuracy of extracted river widths is assessed using different statistical indicators such as the R-square (R²) value, root mean square error (RMSE), mean bias error (MBE). The results show the integrity of the extracted small river surface by the RNDWI index is optimal. Overall, the statistical evaluation indicates the accuracy of the extracted river widths is satisfactory. The effective river width that can be accurately extracted based on satellite images is three times the image resolution. Sentinel-2 MSI images with a spatial resolution of 10 m are used to find that the rivers over 30 m wide can be connectedly, accurately extracted with the proposed method. Results of this work can enrich the river width database in the northeast Tibetan Plateau and its boundary region. The river width information may provide a foundation for studying the spatiotemporal changes in channel geometry of river systems in high-mountain regions. They can also supplement the necessary characteristic river widths information for the river network in unmanned mountain areas, which is of great significance for the accurate simulation of the runoff process in the hydrological model.

Significance: Fine-grained sediment transport systems (grain size under 2,000 μm) are ubiquitous over time and space on Earth and extraplanetary surfaces, and include rivers, deltaic coastal settings, and submarine, lahar, and subglacial systems. Forecasting the evolution of Earth’s surface requires a predictive algorithm for sediment transport. Herein we provide a universal relation for sediment transport in fine-grained rivers. Surprisingly, it is shown that sediment flux differs by up to 2 orders of magnitude as grain size changes only slightly near the boundary between very fine sand and fine sand. The universal applicability of the sediment transport formulation enables quantitative understanding of the sedimentology and morphology of fine-grained rivers.