[1] This study analyzes tide transformation in the Guadalquivir estuary (SW Spain). When fresh water discharges are less than 40 m 3 /s, the estuary is tidally-dominated (flood-dominated) and well mixed. Under such conditions, the estuary can be divided into three stretches, each characterized by a different tide propagation process. In the first stretch of 25 km, the dominant process is diffusion. In the next stretch, approximately over 35 km length, convergence and friction processes are in balance. At the head of the estuary, in the last stretch, the tidal motion is partially standing because of tidal reflection on the Alcalá del Río dam, located 110 km upstream from the estuary mouth. The reflection coefficient R varies with the frequency; for diurnal constituents its magnitude |R D | is 0.25; this value increases in the case of semi-diurnal (|R S | ≈ 0.40), and quarter-diurnal constituents (|R Q | ≈ 0.65), and reaches its minimum at the sixth-diurnal components (|R X | ≈ 0.10). The tidal reflection can generate residual currents that have consequences in the bed morphology. Furthermore, when the fresh water discharges are greater than 400 m 3 /s, the estuary is fluvially-dominated and the water level can be calculated as the linear superposition of tide and river contributions. However, superposition arguments do not hold for currents at any point in the estuary.

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Some aspects of the time‐spatial variability of the phase speed of the internal bore generated almost every tidal cycle in Camarinal Sill, are revised using a set of high resolution experimental data collected in two different positions of the Strait during May 2003. This variability is mainly driven by the intense tidal currents, comparable with the intrinsic propagation velocity of the first mode baroclinic bore. It is shown that the importance of the diurnal tide in the Strait of Gibraltar induces a considerable diurnal inequality on the bore velocity, with an observed maximum difference of 0.7 ms−1 between the speed of two consecutives bores propagating along the eastern part of the Strait. A regularly spatial pattern has been also found: the internal bore reaches its maximum velocity in Tarifa Narrows. A theoretical estimation predicts an extreme phase speed of 2.6 ms−1 during our period of study.

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