Amplification of downstream flood stage due to damming of fine-grained rivers

• Published in: Nature communications Vol. 13; no. 1; p. 3054
• Main Authors: Ma, Hongbo, Nittrouer, Jeffrey A., Fu, Xudong, Parker, Gary, Zhang, Yuanfeng, Wang, Yuanjian, Wang, Yanjun, Lamb, Michael P., Cisneros, Julia, Best, Jim, Parsons, Daniel R., Wu, Baosheng
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-06-2022; Nature Publishing Group; Nature Portfolio
• Subjects: 704/242; 704/286; 704/4111; 704/844/4081; Amplification; Channel morphology; Dams; Downstream; Flood control; Flood predictions; Flood stages; Floods; Floodwater; Flow resistance; Humanities and Social Sciences; multidisciplinary; Rivers; Science; Science (multidisciplinary); Water conveyance
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-022-30730-9

River dams provide many benefits, including flood control. However, due to constantly evolving channel morphology, downstream conveyance of floodwaters following dam closure is difficult to predict. Here, we test the hypothesis that the incised, enlarged channel downstream of dams provides enhanced water conveyance, using a case study from the lower Yellow River, China. We find that, although flood stage is lowered for small floods, counterintuitively, flood stage downstream of a dam can be amplified for moderate and large floods. This arises because bed incision is accompanied by sediment coarsening, which facilitates development of large dunes that increase flow resistance and reduce velocity relative to pre-dam conditions. Our findings indicate the underlying mechanism for such flood amplification may occur in >80% of fine-grained rivers, and suggest the need to reconsider flood control strategies in such rivers worldwide.
Dams constructed on fine-grained rivers cause an increase in flow resistance downstream, thereby amplifying, rather than reducing, flood stage.