![]() ![]() Tides that propagate into the upper estuaries are subject to tide-river interactions (TRIs), resulting in the modulation of tidal amplitudes at specific tidal frequencies by bottom friction and river flow ( Godin, 1999 Horrevoets et al., 2004). Prandle and Wolf (1978) used a one-dimensional model to show that TSI is mainly produced by the quadratic friction effect followed by the shallow water and advective effects, and that the shallow water and advective effects can be dominant on rising tides, while quadratic friction can be prominent on high tides. The degree of total water level modulation due to TSI is also site-specific and varies with surge height and tidal ranges ( Keers, 1968 Prandle and Wolf, 1978). (2013) applied a statistical method to the hindcast over 1959–2005 in the Irish Sea and found that surges tend to peak at a particular phase of tide irrespective of the timing of the storm landfall but with site specificity. Horsburgh and Wilson (2007) gave a first-order explanation of the surge cluster that occurs with rising tide based on the phase shift of the tidal signal (the effect of surge on tides) combined with the modulation of surge production due to the change in water depth (the effect of tides on surge). In an early study conducted in the North Sea and River Thames, United Kingdom, observed TSI was found to amplify surge height significantly on rising tides, independent of initial surge height or the relative phase difference between tides and surges ( Proudman, 1955). The characteristics and mechanisms of tide-surge interactions (TSIs) have been widely studied during recent decades ( Proudman, 1955 Prandle and Wolf, 1978 Wolf, 1978 Idier et al., 2012 Zhang et al., 2020). Furthermore, such non-linear interaction is sensitive to sea level rise, storm intensity, and river flow as a result of climate change ( Yang et al., 2014 Li et al., 2020), which makes the flood hazard risk even more complex and unpredictable. The total water levels could be increased or decreased by the non-linear interactions between storm surges, river flow, and tides. Non-linear interactions are known to exist between tides, storm surge, and river flow, but understanding of how non-linear interactions exacerbate the compounding effect is limited. Coastal flood risks associated with compound flooding cannot be simply estimated by superposition of astronomical tides and river-induced and storm-surge-induced water levels. The co-occurrence of storm surge and river flooding may cause compound flooding ( Bevacqua et al., 2019), which results in extreme water levels caused by non-linear interactions of storm surges, river flood, and astronomical tides ( Doodson, 1956 Proudman, 1957 Rossiter, 1961 Johns et al., 1985 Arns et al., 2020). population living in low-lying coastal areas. ![]() The transition zone of damping and enhancing effects shifted downstream as the river flow rate increased.Ĭoastal flooding hazards caused by tropical cyclones present a severe risk to nearly 40% of the U.S. ![]() Furthermore, sensitivity analysis was carried out to evaluate the effect of river flooding on the non-linear interactions. Evident compound flooding was observed as a result of non-linear tide-surge-river interactions. Tide-river interactions suppressed the water level upstream while tide-surge interaction increased the water level downstream, which resulted in a transition zone of damping and enhancing effects where the tide-surge-river interaction was prominent. Model results indicated that tide-river interactions damped semidiurnal tides, while the tide-surge interactions mainly influenced diurnal tides. Non-linear interactions between tide-surge-river were investigated using a non-stationary tidal analysis method, which decomposes the interactions’ components at the frequency domain. ![]() The model was validated with tide gauge data in the estuary for selected hurricane events. To better understand the contribution of non-linear tide-surge-river interactions to compound flooding, the unstructured-grid Finite Volume Community Ocean Model was applied to simulate coastal storm surge and flooding in the Delaware Bay Estuary in the United States. Low-lying coastal areas in the mid-Atlantic region are prone to compound flooding resulting from the co-occurrence of river floods and coastal storm surges. 3Pacific Northwest National Laboratory, Earth Sciences Division, Richland, WA, United States.2Department of Civil and Environmental Engineering, University of Washington, Seattle, WA, United States.1Pacific Northwest National Laboratory, Coastal Sciences Division, Seattle, WA, United States.Ziyu Xiao 1, Zhaoqing Yang 1,2*, Taiping Wang 1, Ning Sun 3, Mark Wigmosta 2,3 and David Judi 3 ![]()
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