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This paper investigates the impact of the bridge-pilling modifications on the tidal flow at the strait of a human-altered mesotidal estuary (Cádiz Bay, Spain). The analysis was accomplished by combining (1) field data of current velocities in a cross-section close to the pile of a recently built bridge, and (2) hydrodynamics results from the calibrated and tested DELFT3D numerical model on the study site. The analysis was focused on bridge piling effects at intratidal scale during neap and spring tides. Semidiurnal (D2), quarti-diurnal (D4) and sixth-diurnal (D6) bands were examined. The ratio of quarter-diurnal to semidiurnal amplitudes (D4/D2) is largest (¿1) near the bottom of the channel due to friction, and the ratio D6/D2 is largest (¿1.5) close to the pile and in the shallowest part of the cross-section, due to internal asymmetry and tidal advective accelerations. Comparing neap and spring tides, the most marked asymmetries are found in the latter. These asymmetries occur around the wake of the pile, alternating from flood to ebb. The location of the bridge pile causes a decrease in the amplitude of D2 (50%), and a phase lag in the tidal wave of 30 min. The D6 amplitude increases up to almost 100% due to distortion of the tidal wave induce by the wake created at the pile. Moreover, the pile reduces about 1 m the depth where the pycnocline is observed. Additionally, the pile can be considered as an obstacle for the sediment flux. These effects can be extrapolated to similar infrastructures, such as wind or wave energy farms, that can potentially modify the estuarine dynamics. • Tidal flow is modified by a bridge piling in an estuary. • The M2 tidal amplitude is reduced up to 50% near the pile. • The pile causes a 30-min phase lag in the pile wake. • The sixth-diurnal tidal band increases up to 100%. • The center of the pycnocline is deepened by 1 m. [ABSTRACT FROM AUTHOR]

Abstract: A background knowledge of marine dynamics helps harbour managers to control pollution and to manage dredging and traffic operations. This contribution studies the hydrodynamic conditions within Bilbao Harbour, which is enclosed by the Nervión Estuary (in the Basque Country, Spain). The results obtained from hydrographical surveys are compared with numerical simulations obtained using the Regional Ocean Modelling System (ROMS). Hydrodynamic modelling was carried out to determine the inner harbour currents for a specific period in which data were available. Then, numerical experiments were designed in order to quantify the importance of different driving mechanisms in the harbour hydrodynamics. The results show that, in addition to the strong tidal influence on water circulation, the wind forcing and freshwater discharge also have a non-negligible influence on the currents. The computational domain is complex due to the presence of harbour infrastructures (i.e. breakwaters and piers). As a result, topographic eddies are therefore observed in the results. The freshwater influence of the Nervión river can also be observed in residual currents. This paper presents an improvement to the application of numerical modelling to a complex geometry domain, contributing to our understanding of the behaviour of the marine systems in meso-tidal harbours. This can be used to deal with harbour engineering and management problems. [Copyright &y& Elsevier]