Strong Inland Propagation of Low‐Frequency Long Waves in River Estuaries

• Published in: Geophysical research letters 2020-10, Vol.47 (19), p.n/a
• Main Authors: Guo, Leicheng, Zhu, Chunyan, Wu, Xuefeng, Wan, Yuanyang, Jay, David A., Townend, Ian, Wang, Zheng Bing, He, Qing
• Format: Article
• Language: English
• Subjects: Amplitudes; Astronomical tides; Damping; Decay rate; Electromagnetic wave filters; Estuaries; Estuarine dynamics; Flood control; Flood management; Frequency filters; Long waves; low‐frequency; Mathematical models; MSf; Numerical models; River channels; river discharge; River flow; Rivers; Stream flow; subtidal friction; Tidal rivers; Tidal waterways; Tidal waves; Tides; Wave propagation
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2020GL089112

Tidal waves traveling into estuaries are modified by channel geometry and river flow. The damping effect of river flow on incident astronomical tides is well documented, whereas its impact on low‐frequency tides like MSf and Mm is poorly understood. In this contribution, we employ a numerical model to explore low‐frequency tidal behavior under varying river flow. MSf and Mm are locally generated by frictional mechanisms inside an estuary, and they are larger in amplitude far upstream in tidal rivers and persist landward of the point of tidal extinction. Increasing river flow nonlinearly modulates the longitudinal variations of MSf and Mm amplitudes. This is dynamically explained by flow‐enhanced asymmetry in subtidal friction over the spring‐neap (MSf) and perigee‐apogee (Mm) cycles, respectively. Estuaries act as frequency filters, where low‐frequency waves decay at a smaller rate and propagate more inland than high‐frequency waves. Strong inland penetration of low‐frequency tides informs compound flood management. Key Points High river flow stimulates local generation of significant low‐frequency tides particularly in upstream tidal river part of estuaries Varying river flows nonlinearly modulate longitudinal variations of MSf amplitude by enhancing fortnightly asymmetry in subtidal friction Strong inland penetration of low‐frequency tidal waves and surges beyond the limit of incident waves informs management of compound flood