A three-dimensional numerical model, based on Delft3D code, has been implemented and calibrated in the mesotidal Guadalquivir Estuary (Spain), a tidally-driven estuary due to the reduced freshwater discharges (25 m3s-1 year-round average), which are subject to human regulation at the dam located at its head. The model has been applied to study in detail some estuarine features for low freshwater discharges: the first one is the non-linear interaction of semidiurnal constituents, which results in a tidal amplification factor (ratio of local amplitude to the amplitude at the mouth) that depends on the spring-neap tidal cycle, with markedly larger values during neap tides. The second one is the analysis of tidal resonance in the estuary, extending previous studies on the topic, which shows that resonance occurs at near-diurnal frequencies. The peak of resonance decreases in magnitude and shifts towards lower frequencies as friction increases, either by increasing the friction coefficient itself or the amplitude of the tide.
