Overtide Generation in Small Inlet-Bay Systems

Abstract

The generation of shallow water tides (overtides) may influence shoaling processes in shallow embayments and harbors. A simplified, conceptual model is developed to simulate the generation of overtides and tidal asymmetries in small inlet/bay systems. The model’s formulation assumes a weakly nonlinear, pumping-mode response and includes effects of four generating mechanisms: quadratic bottom friction (QB), elevation-effect of friction (EEF), nonlinear continuity (NC), and advective acceleration (AA). QB generates primarily odd harmonics, including a second overtide component (M6) that reduces/distorts peak flood/ebb currents symmetrically. The first overtide component (M4) is generated primarily by NC, EEF, and AA. NC, AA, and QB mechanisms are associated with flood-dominant distortion patterns, whereas the EEF mechanism is associated with a shift toward ebb dominance in the special case in which NC contributions are reduced (e.g., large basin tidal flats) and AA is small. Solutions for the M4 tide indicate phase-locking, and distortion patterns consistent with previous studies. A maximum flood-dominant response can occur when the ocean forcing frequency is half the Helmholtz frequency, which is a condition that may cause flood shoals to develop.