Multiscale Temporal Response of Salt Intrusion to Transient River and Ocean Forcing. Issue 3 (7th March 2022)

• Record Type: Journal Article
• Authors: Payo‐Payo, Marta; Bricheno, Lucy M.; Dijkstra, Yoeri M.; Cheng, Weicong; Gong, Wenping; Amoudry, Laurent O.
• Is Part Of: Journal of geophysical research. Volume 127:Issue 3(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-03-07
• Subjects: estuarine salt intrusion -- wavelet analysis -- transient response -- numerical model; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2021JC017523
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: Salt intrusion in surface waters endangers freshwater availability, influences water quality, and affects estuarine ecosystem services with high economic and social values. Salt transport and the resulting salinity distributions result from the non‐linear interactions between salt and water dynamics. Estuaries are often considered under (quasi)‐steady assumption or by focusing on specific timescales. Our understanding of their temporal multiscale response to transient forcing is limited, which hinders the implementation of effective mitigation strategies. We apply wavelet analyses to quantify the variability of salt intrusion from hourly to seasonal timescales and unravel the temporal variability of its response across scales. We focus on an estuary that undergoes significant transient forcing, the Modaomen estuary in the Pearl River Delta, and apply the wavelet analyses to year‐long data generated by a coastal ocean numerical model. Our results show that this estuary responds to changes in tidal and riverine forcing throughout the year over interwoven timescales. Our results highlight the temporal variability of the salt intrusion response time both within a given regime and for the transition between regimes. They also suggest that tides control the response time more strongly than river discharge, even though river discharge determines the magnitude of the salt intrusion, and thus modulates the evolution of the salt intrusion response time. We propose a broadly applicable framework to calculate response times with simple data. These results can provide a first‐order guidance for design and implementation of estuarine management strategies and mitigation measures that ensure water access and facilitate sustainable development. Plain Language Summary: With more and more people living by coast, more water resources are needed, and the fragile equilibrium of estuaries and coastal ecosystems is at risk. In estuaries and deltas, the salty water from the ocean meets the fresh water from the river and can propagate upstream. We call this salt intrusion. One of the solutions used to control salt intrusion is releasing water to push the salt intrusion back, but for this to be effective it needs to be well timed. We use a computer model to understand how the changes in river and ocean affect how far and when the salty water reaches upstream. We show that the river determines how far it reaches but it is mostly the tide that determines when this will happen. Since the ocean moves at different scales, the salt intrusion also responds at multiple scales with different time delays, and it is difficult to distinguish one from another because they overlap. The time delays are not constant and evolve throughout the year. We need to consider the multiple overlapping scales and the evolving time response to ensure the sustainable management of estuaries. Key Points: We analyze the multiscale temporal response of salt intrusion to transient river and ocean forcing during dry and wet season The salt intrusion response time evolves over time throughout the year both within regimes and across regimes This response time is mainly controlled by tidal forcing and indirectly modulated by river forcing