Tide transformation in the Guadalquivir estuary (SW Spain) and process‐based zonation

Abstract

[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.

Frictional interactions between tidal constituents in tide-dominated estuaries

“…The amplitude and phase of tidal constituents near the mouth are highly similar to those at the entrance of the Guadiana estuary (Table 2), producing a semidiurnal and mesotidal signal with a mean spring tidal range of 3.5 m. In this paper, the tidal observations of the Guadalquivir estuary are taken directly from Diez-Minguito et al (2012). The results apply to the low river discharge conditions (< 40 m 3 s −1 ) that usually predominate in the estuary.…”

“…The estuary has a length of 103 km starting from the mouth at Sanlúcar de Barrameda to the Alcalá del Río dam. The geometry of the Guadalquivir estuary can be approximated by exponential functions with a convergence length of a = 60 km for the cross-sectional area and b = 66 km for the width (see Diez-Minguito et al, 2012). The flow depth is more or less constant (7.1 m).…”

Reservoir impacts downstream in highly regulated river basins: the Ebro delta and the Guadalquivir estuary in Spain

“…in significant suspended sediments concentration in the river. Figure 4 shows the relationship between the mean daily flow delivered by Alcalá del Río and the suspended sediment concentration during 1993-2007. However, significantly higher concentrations are usually found along the estuary, in which the dramatic decrease of freshwater delivery from the catchment has altered the sediment dynamics and budget, two turbidity maximum areas found (Díez-Minguito et al, 2012), and tidal dynamics influencing both salinity and sediments dynamics (Díez-Minguito et al, 2013, 2014, with turbidity events that may persist over weeks after a flooding event. Contreras and Polo (2012) reported values up to 14 and 9 g L −1 at the upper and mediumlow reaches of the estuary.…”

Frictional interactions between tidal constituents in tide-dominated estuaries

“…The estuary has a length of 103 km starting from the mouth at Sanlucar de Barrameda to the Alcala del Rio dam. The geometry of the Guadalquivir estuary can be approximated by exponential functions with convergence length of a=60 km for the cross-sectional area and b=66 km 155 for the width (see Diez-Minguito et al, 2012). The flow depth is more or less constant (7.1 m).…”

“…Tidal dynamics along the Gualdalquivir estuary was analysed by Diez-Minguito et al (2012) based on harmonic analyses of field measurements collected from June to December 2008. The amplitude and phase of tidal constituents near the mouth are highly similar to those at the entrance of the Guadiana estuary ( term on the velocity, u|u|.…”