Subtidal variability in water levels inside a subtropical estuary

Abstract

Year-long time series of water level are analyzed at five locations along the St. Johns River Estuary, Florida, to investigate propagation of subtidal pulses. Hilbert-transformed Empirical Orthogonal Functions (HEOFs) are obtained after a dominant seasonal signal is extracted from the data. These functions provide information on spatial structure and propagation phase of subtidal water level pulses. The first HEOF mode explains 96% of the subtidal variability and features an unusual spatial structure: amplitude attenuation (averaging 1 mm/km) to 55 km upstream, slight amplification (0.16 mm/km) over the middle 70 km, and attenuation (2.3 mm/km) over the final 18 km of the estuary. The phase suggests a shift from progressive to quasistanding wave behavior at 55 km from the estuary mouth. Additionally, local minima in the phase suggest two sources of subtidal forcing: the coastal ocean and the upstream end. An analytical model describing the evolution of long waves through a channel with frictional damping is fit to the amplitude of HEOF mode 1. Solutions are obtained as a function of two parameters: the nondimensional length of the basin, j, and the nondimensional frictional depth, d. Values of j between 0.55 and 0.67 and d between 1.45 and 1.7 provide the best fit with the HEOF results (1% error or less). These values indicate a highly frictional environment in which the average subtidal wavelength is 10 times the basin length. Subtidal pulses in this estuary, therefore, behave as damped waves that can be represented with idealized models.

To What Extent Multidecadal Changes in Morphology and Fluvial Discharge Impact Tide in a Convergent (Turbid) Tidal River

“…The development and widespread use of nonstationary tidal analysis methods (Appendix A gives a brief overview of methods used to calculate tidal components) match the present-day research effort to understand the interactions of river discharge with tides. River discharge influences both the tidal and subtidal water levels (Alebregtse & de Swart, 2016;Henrie & Valle-Levinson, 2014;Jay & Flinchem, 1997;Ross & Sottolichio, 2016), enhances tidal friction, thereby damping tidal energy and tidal range (Cai et al, 2012(Cai et al, , 2014Godin, 1991;Savenije et al, 2008), decreases wave celerity (Godin, 1985;Savenije et al, 2008), and controls tidal interactions by dissipating the principal tidal constituents and favoring energy transfer from the principal bands to the lower and higher frequencies (Guo et al, 2015(Guo et al, , 2016. This generation of overtides and compound tides is favored until they reach a point upstream where they are damped more rapidly by friction than they are generated through the nonlinear interactions (Matte et al, 2014).…”

Cold Front Driven Flows Through Multiple Inlets of Lake Pontchartrain Estuary

“…A study for a semienclosed homogeneous, rotating basin by Sanay and Valle‐Levinson (), investigated the wind effect on hydrodynamics. Subtidal flows in estuaries and subtropical lagoons have been examined with ADCP data in many studies (e.g., Henrie & Valle‐Levinson, ; Li et al, ; Murphy et al, ; Sepulveda et al, ). In these studies, however, the wind effects were discussed without attention to the details of the weather systems.…”

Tidal and Subtidal Variations in Water Level Produced by Ocean‐River Interactions in a Subtropical Estuary

“…Factors that can modify salinity distribution are, among others, the variability of river discharge by dam regulation and precipitation fluctuations and by changes in depth through sea‐level rise or dredging (van Rijn, 2011). The effects of sea‐level rise in an estuary may be explored by understanding the interactions of river discharge and forcing from the ocean at tidal and subtidal time scales (Henrie & Valle‐Levinson, 2014). Subtidal time scales refer here to any periods greater than tidal periods, that is, >26 hr.…”

“…The aim of the present work is to study phase propagation in tidal and subtidal signals. It has been demonstrated that subtidal pulses from the ocean do propagate along estuaries (Henrie & Valle‐Levinson, 2014). Wind‐induced subtidal levels over the continental shelf (e.g., set‐up or set‐down) may propagate along estuaries in the form of free waves (Wong & Valle‐Levinson, 2002) with periodicities of 2–4 days or even longer, such as 5–20 days (Garvine, 1985).…”