Since 1953, an equation has been used to explain the relationship between hydraulic parameters (river width, depth, and velocity) and river discharge, the volume of water that flows through a river channel. This relationship is called at-a-station hydraulic geometry (AHG). Understanding this relationship is important for hydraulic engineering, predicting flooding, navigation, and more.
Though this equation has been studied extensively through field research, this has limited sample size and study areas and is not enough to fully explain the variety of factors beyond hydraulic parameters that impact river discharge. The ability to use satellites to monitor the surface of the earth through remote sensing may provide an option to expand the way AHG is understood. The data was presented in a paper published in the Journal of Remote Sensing.
"Understanding the response of width to changing discharge in different rivers is crucial for hydraulic modeling and river management. However, previous research is limited in spatiotemporal coverage by field measurements and only offers a fragmentary understanding in confined areas. This study introduces new data sources—multi-temporal river width data derived from Landsat and global discharge observations built upon years of progresses by the community —to provide a more comprehensive scope," said Zimin Yuan, a researcher at the Institute of Remote Sensing and Geographic Information Systems at Peking University in Beijing, China. By using several data sets covering years ranging from 1979 to 2020 and matching data against Google Map Images to find limitations, researchers were able to derive an unprecedented global samples of AHG.
18 variables relating to AHG were identified from a vast range of factors, which could be divided into six categories that included: hydrology, physiography, climate, land cover, geology, and human influences. To focus the list of variables, researchers looked at the relationship between each variable and how it impacts the AHG. Then, because AHG is also closely related to the planform river pattern, researchers also factored in whether a river was meandering, anabranching, straight, or braided.
Understanding how these identified factors are related is essential for predicting river width changes, which can have impacts on the land and communities around the river. "We found that a 1% increase in discharge will result in a median of 0.2% increase in river width worldwide. Reaches characterized by cohesive soil, high forest coverage, and less human influences typically exhibit weaker response of width to discharge changes. River planform patterns are correlated with width response, and the relationship can be well correlated by climatic conditions," said Yuan.
Looking ahead, researchers are hoping to understand the changes in river width over time, which is impacted by channel shape. They also plan to explore the abilities of remote sensing to find other factors that influence river discharge. "We plan to explore the depth response to discharge using remote sensing in the future. We also hope to reconstruct global channel shape on the basis of the samples and knowledge obtained in this and following studies," said Yuan.
Other contributors include Peirong Lin of the Institute of Remote Sensing and Geographic Information Systems at Peking University; Xiwei Guo at the Department of Geosciences at The Pennsylvania State University; Kai Zhang at Geovis Environment Technology Co. Ltd.; and Hylke E. Beck at the Physical Science and Engineering Division of King Abdullah University of Science and Technology.
The National Natural Science Foundation of China, the Beijing Nova Program, and the Yunnan Provincial Science and Technology Project at Southwest United Graduate School funded this research.
