Nonlinear Interaction Between the Tide and the Storm Surge with the Current due to the River Flow in the Río de la Plata

Abstract

The Rio de la Plata estuary (RdP) is characterized by the large flow of its tributary rivers (Q), with an average of 22,000 m3 s− 1 and an interannual variability range from 8000 to 90,000 m3 s− 1. In this work, the hypothesis that the current due to that flow (CDR) interacts nonlinearly with both the tides and storm surges is evaluated utilizing water level observations and numerical simulations. Two tide gauge time series gathered at the freshwater tidal zone (FTZ) of the RdP are analyzed with the novel surrogate analysis. The analysis is applied for periods of high, medium and low Q. Results show that both interactions occur at the upper half of the FTZ and increase with Q. Harmonic analyses support the surrogate analysis’ conclusions and show that tide-CDR interaction redistributes the energy among tidal harmonics, increasing asymmetry. Numerical simulations confirm that (i) both interactions maximize at the upper half of the FTZ and decrease downstream; and (ii) they are modulated by Q; a rise of about 14,000 m3 s− 1 (interquartile range) can produce an intensification of 50% and 100% of the amplitudes of the tide-CDR and surge-CDR interactions, respectively; and (iii) both interactions introduce asymmetries in the water level, with faster rises and slower falls; (iv) the quadratic bottom friction is the main source of both interactions; (v) tide-CDR interaction represents 12% of the water level associated with the tide, whereas surge-CDR interaction accounts for 5% of the surge peak; and (vi) the interactions are significant in the upper FTZ because there, the magnitude of the currents associated with the tide and the surge are comparable to CDR; downstream, the channel widens and CDR decreases.