Salt intrusion and its controls in the macro-tidal Oujiang River Estuary, China
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Salt intrusion and its controls in the macro-tidal Oujiang River Estuary, China Yichun Li 1 & Jingui Liu 2,3 Received: 18 February 2020 / Accepted: 24 August 2020 / Published online: 17 September 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The Oujiang River Estuary (ORE) is a macrotidal estuary in southeast Zhejiang Province of China. Although the economy has developed rapidly over the past two decades, few studies have been explored on the estuarine dynamics. Based on in situ measurements, we established a 3-D numerical model to investigate salt intrusion and its response to river discharge, tide, and the salinity at river mouth. We obtained following conclusions. (1) Although salt intrusion length followed a power law with respect to overall river discharge span capturing the fundamental trend, salt intrusion length should be analysed at different ranges of river runoff, as regression accuracy increased substantially at individual range. (2) Estuarine salt transport was dominated by two components of downstream Euler flux and upstream Stokes flux, while tidal shear effects and tidal pumping contributed less. (3) Salt intrusion length not only was a function of river runoff and tidal range but also influenced, with more indicating significance, by mouth salinity. Additionally, geometry effect and nonlinearity might amplify the strong dependences of salt intrusion on mouth salinity and tidal range. (4) Results from partial least squares revealed an approximately linear relation between salt intrusion length and the determining factors of tidal range, river runoff, and river mouth salinity. The hysteretic term was found to have most important influence on salt intrusion length. The response time of salt intrusion in ORE varied with runoff from ~ 2.5 days for medium discharge to ~ 1 day for large and small discharges. Keywords Oujiang River Estuary . Salt intrusion . FVCOM . Partial least squares . Stokes transport
1 Introduction In estuaries, saltwater intrudes upstream during flood tide. Estuarine salt intrusion is dependent on hydrological conditions such as river flow and tide and bathymetry and their natural or artificial changing behaviours. River discharge pushes the saltwater downstream while estuarine gravitational circulation and tidal dispersion drive ocean water into the estuary (Guerra-Chanis et al. 2019). The pattern of salt intrusion may be altered by dredging, barrier construction or flow regulation as well. Salt intrusion is one of the most important ODYN-D-20-00024R2 * Jingui Liu [email protected] 1
Key Laboratory of Habor, Coastal and Offshore Engineering, Beibu Gulf University, Qinzhou, Guangxi 535011, China
2
National Marine Environmental Forecasting Center (NMEFC), Ministry of Natural Resources (MNR), Beijing 100081, China
3
Key Laboratory of Marine Hazards Forecasting, NMEFC, MNR, Beijing 100081, China
components of estuarine processes and has a significant influence on freshwater utilization, ecosystem protection and estuarine management. The length of sa
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