Impact of Intertidal Areas on Tidal Propagation in Tidally Dominated Estuaries. Part I: Theoretical Formulation

Intertidal zones, such as saltmarshes and mudflats, face significant pressure from climate change and human activities, threatening the sustainable functioning of estuarine ecosystems. Using a one-dimensional analytical model that resolves the coupled tidal motions in the channel and intertidal areas, we systematically investigated the impact of intertidal zones on tidal propagation in tidally dominated estuaries. Unlike previous analytical studies considering only the effect of water storage over intertidal areas (IWS), our model resolves both IWS and the water exchange between the channel and intertidal areas due to longitudinal currents over intertidal areas (ILC). Our analytical solution demonstrates intertidal zones increase the complex tidal wavenumber () through the width and water flux ratios between the intertidal and channel regions, representing the IWS and ILC effects, respectively. The effects of intertidal areas on depend on the relative importance of local inertia, width convergence, and bottom friction. In weakly dissipative, weakly convergent estuaries, increases in induced by intertidal zones bring estuaries closer to resonance when the real part of
(with the estuary length) is below its resonance threshold (amplifying tides) and move them further from resonance when above (damping tides). In strongly dissipative, weakly/moderately convergent estuaries, intertidal areas consistently cause tidal damping by increasing. In weakly/moderately dissipative, strongly convergent estuaries, tides are hardly influenced by intertidal zones. The ILC effect reduces, thereby partly counteracting the aforementioned overall effects of intertidal areas. A comprehensive sensitivity analysis of the ILC process is conducted in Part II of this study.