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|Short- and Long-Term Effects of Freshwater Discharge on Sea-Level Variability in Back-Barrier Estuaries|
Oudijk, E. (2021). Short- and Long-Term Effects of Freshwater Discharge on Sea-Level Variability in Back-Barrier Estuaries
. MSc Thesis. NIOZ Royal Netherlands Institute for Sea Research: Yerseke. 72 pp.
Measures to prevent sea level rise from causing societal and ecological damage are needed to protect vulnerable, coastal communities. Many of these communities are located at back-barrier estuaries. To choose the correct measures, it is important to know the local trend in sea level rise. However, this is difficult due to the strong interannual variability of the local sea level. Part of this variability is explained by atmospheric effects (wind and pressure) on the sea level. Previous studies show that after removing the variability associated with winds and atmospheric pressure (for example by multiple linear regression) still a large variability remains. In this work, it is shown that this interannual variability can be reduced by considering the long-term effect of fresh water discharged into the back-barrier system. The Dutch Wadden Sea (DWS) is used as a test case. The long term effect of freshwater discharge on the local sea level has been unknown until now due to a lack of observational data spanning several years with a high spatial and temporal resolution. In this work, 35 years of data of the DWS from validated three-dimensional baroclinic numerical simulations was used. A correlation coefficient R = 0.7 is found between the sea set-up, after being corrected for atmospheric effects, and the fresh water discharged into the (back-barrier) DWS on a timescale of 35 years. Correlations do not prove a causality, but the strong correlations are supported by results of an idealized analytical model that also show that the input of fresh water in a back-barrier estuary creates a set-up in sea level. The set-up caused by freshwater discharge is in the order of centimeters for the DWS, and is relevant for predicting the local sea-level rise. The results can be used for planning and restoring projects, making funding decisions, and prioritizing investments with the final goal to protect coastal communities.