Exploration of Tidal‐Fluvial Interaction in the Columbia River Estuary Using S_TIDE

Abstract

Numerous tidal phenomena, including river tides, internal tides, and tides in ice-covered bay, are nonstationary, which pose a great challenge for traditional tidal analysis methods. Based on the independent point scheme and cubic spline interpolation, a new approach, namely the enhanced harmonic analysis, is developed to deal with nonstationary tides. A MATLAB toolbox, S_TIDE, developed from the widely used T_TIDE, is used to realize the approach. The efficiency of S_TIDE is validated by analyzing a set of hourly water level observations from stations on the lower Columbia River. In all stations, the hindcast of S_TIDE is more accurate than NS_TIDE that is a powerful nonstationary tidal analysis tool adapted to river tides. The changing mean water level and tidal constituent properties obtained by S_TIDE are similar to those obtained by NS_TIDE, continuous wavelet transform, and empirical mode decomposition and highly consistent with theory on river tides. Moreover, different from NS_TIDE that only can be applied to river tides, enhanced harmonic analysis is free of dynamic content, assuming only known tidal frequencies. Therefore, S_TIDE can be applied to all kinds of nonstationary tides theoretically. Though powerful, S_TIDE also has some limitations: S_TIDE cannot be used for prediction and too many independent points in S_TIDE may induce computational memory overflow and unrealistic results.Plain Language Summary Based on the independent point scheme and cubic spline interpolation, a new approach, enhanced harmonic analysis, was developed to deal with nonstationary tides. Enhanced harmonic analysis is realized by a MATLAB toolbox, S_TIDE, which is developed from the widely used T_TIDE. S_TIDE assumes only known tidal frequencies and theoretically can be applied to all kinds of nonstationary tides and stationary tides. In this study, S_TIDE is applied to analyzing records of river rides that is one of the simplest kinds of nonstationary tides for which ample data are available. The method is compared with other methods to show its efficiency.

Seasonal variation of the principal tidal constituents in the Bohai Sea

“…In this study, the EHA developed in Jin et al (2018) and Pan et al (2018b) was further improved in order to resolve more tidal constituents by adding the minor constituents whose harmonic parameters were assumed to be constant and calculated together with the temporally varying harmonic parameters of the principal tidal constituents. The nodal and astronomical argument corrections were embedded into the least square fit to eliminate the influences of nodal cycle and linearly varying astronomical argument.…”

“…In contrast, the harmonic parameters are assumed to be constant in CHA and constant within each month in SHA. A MATLAB toolkit, S_TIDE, was released to realize EHA by Pan et al (2018b). In this study, nodal and astronomical argument corrections are embedded into the least square fit, following Foreman et al (2009); in addition, the harmonic parameters of the minor tidal constituents are assumed to be constant and calculated together with the temporally varying harmonic parameters of the principal tidal constituents to resolve more constituents and retain compu-4 D. Wang et al: Seasonal variation of the principal tidal constituents tational stability.…”

“…Similar to Jin et al (2018) and Pan et al (2018b), the independent point scheme and cubic spline interpolation are used to jointly solve the temporally varying and constant harmonic parameters, which are not shown here for brevity. As mentioned in Pan et al (2018b), the temporally varying harmonic parameters obtained using EHA with different numbers of independent points represent fluctuations on different timescales. In this study, six independent points are used to obtain the seasonal variability of the principal tidal constituents.…”

Seasonal variation of the main tidal constituents in the Bohai Bay

“…Through combining CHA with the independent point scheme and cubic spline interpolation, Jin et al (2018) developed enhanced harmonic analysis (EHA) to directly obtain temporally varying tidal harmonic parameters. A MATLAB toolbox, S_TIDE, was released to realize EHA in Pan et al (2018b). As mentioned in Pan et al (2018b), the temporally varying harmonic parameters obtained using EHA with different numbers of independent points represented oscillations on different time scales.…”

“…A MATLAB toolbox, S_TIDE, was released to realize EHA in Pan et al (2018b). As mentioned in Pan et al (2018b), the temporally varying harmonic parameters obtained using EHA with different numbers of independent points represented oscillations on different time scales. Therefore, the seasonal variability of the major tidal constituents will be directly obtained by using EHA with 6 independent points in this study.…”