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Space‐time plots of simulated bed level change (difference) and bed surface grain size change (ratio) due to an erosion‐control measure, relative to a base case without the measure: (a) constant discharge‐unisize sediment; (b, c) constant discharge‐mixed‐size sediment; (d) variable discharge‐unisize sediment; (e, f) variable discharge‐mixed‐size sediment. White space on the plots indicates no change in bed level or grain size.
Source publication
Erosion‐control measures in rivers aim to provide sufficient navigation width, reduce local erosion, or to protect neighboring communities from flooding. These measures are typically devised to solve a local problem. However, local channel modifications trigger a large‐scale channel response in the form of migrating bed level and sediment sorting w...
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Citations
... For example, channelization or levee construction typically narrows down the channel and intensifies bed incision, leading to lower values of b [52]. On the contrary, erosion-control measures have been implemented in many reaches to mitigate channel incision, resulting in aggradation and higher values of b [53]. Despite the complexity of human intervention, our analyses of GDP, nighttime lights, and urban extent point to a clear pattern that urbanized and developed regions are usually distributed around reaches with high b. ...
The power-function exponent b of at-a-station hydraulic geometry (AHG) depicts the temporal response of river hydraulic parameters to changing discharge and is crucial for hydraulic modeling, habitat assessment, and river management. However, previous research, limited by field measurements, offers only a fragmentary understanding of the AHG exponent b in confined areas. Additionally, it remains challenging to establish the correlation between b and the climatic regime of a river. To offer a more comprehensive scope of AHG, this study assesses the width–discharge AHG exponents of 1,568 river reaches by pairing multi-temporal river width data from 1.19 million Landsat images with discharge observations from >17,000 gauge stations worldwide. The results show that b has a median value of 0.213, consistent with values reported in previous regional studies, but it exhibits complex relationships with 3 spatial dimensions—latitude, elevation, and drainage area. We further analyze the spatial variations in b against >200 physiographic and climatic factors, and find that reaches characterized by cohesive soil, high forest coverage, and less anthropogenic influences typically exhibit lower values of b, indicating a weaker response of width to discharge changes. By labeling 4 planimetric river morphologic types globally, we show that braided reaches exhibit the highest median of b, followed by straight, anabranching, and meandering reaches. The differences can be well explained by the climatic conditions of the river reaches as shown on the Budyko curve. This study lays the foundation for AHG research in ungauged regions using satellite remote sensing, expanding global hydraulic data and enhancing the understanding of the spatial variability and influencing factors of hydraulic geometry worldwide.
Most of the rivers in the Polish Carpathians are regulated over long sections by a sequence of grade control structures (GCSs), reducing the channel bed gradient. Their impact on changes in river morphodynamics is still little known. It is usually believed that they interrupt the continuity of the river and thus deteriorate its ecological quality. The aim of this study was to analyze longitudinal and vertical sediment distribution and potential conditions of sediment transport in a mountain river with grade control structures. The influence of hydraulic parameters on particle-size distribution and sediment transport conditions was also examined. The study was carried out in the mountainous, gravel-bed Mszanka River, with an average annual flow of 3.35 m3/s. Along a 5.66-km-long section of this river, 25 concrete GCSs of approximately 1 m in height were constructed. The study included geomorphological mapping of the channel, geodetic surveys and measurements of both surface and unstratified bed material, as well as hydraulic modeling and calculations. The findings showed that the particle size distribution is very complex, with no consistent tendency to either fining or coarsening. The most interesting observation is the lack of armour layer in 10 out of 15 surveyed reaches between GCSs. The material is generally well mixed and even slightly finer on the surface. This contradicts the accepted view that under conditions of low sediment supply such layer always forms. Our hypothesis is that the reduced water surface gradient provided by the GCS system, despite the lack of a regular supply of coarser material, may be a factor in preventing the formation of armouring. The results of the potential transport calculation indicate that at relatively low but frequent Q2 flow, partial transport can occur, but in most reaches involving percentiles of at least φ50. This flow is also responsible for erosion and morphological changes in the channel. This is contrary to the regulation design, which assumed that the channel would be stable under these flow conditions. At Q5 flow, global transport can take place in 10 reaches between GCSs. Correlation analysis showed that transport conditions (maximum particle taken for transport and transport rate) depend mainly on water surface gradient, flow velocity and unit stream power. They are also influenced by the GCS height (negatively) and the length of the reach between GCSs (positively). The regulation with GCSs has resulted in the division of the river into reaches that are differentiated in terms of sediment distribution and conditions for transport. The value of the channel-forming discharge may be different in each reach between GCSs. The findings of our study may be useful in better managing rivers with GCS and in improving their habitat quality.
