Bridge-piling modifications on the momentum balance in an estuary: The role of tides, winds and seasonality

Abstract

Marine structures modify the hydrodynamics in relatively shallow coastal areas such as bays and estuaries, as analyzed here in the Bay of Cádiz. This study explores the momentum balance and the wakes generated by bridge piles, through a validated numerical model of a well-mixed mesotidal estuary. Three main drivers are considered: tides, winds and buoyancy forcing. The results show that the contribution of advection has the same order of magnitude as that of the barotropicity, with baroclinicity being relevant only during summer. The effects of the pile are intensified inside the basin (i.e., the bay) during spring-tides and ebb periods, and outside the bay during neap-tides and flood periods. These changes in the momentum balance reach up to 1 km landward in the deepest areas and up to 2 km seaward in the shallowest areas. The momentum terms vary the most in spring and summer, when wind forcing is weak. Westerly winds coinciding with flood-tide periods increase the advection in the outer basin, because of the pile. In contrast, easterly winds coinciding with the ebbing tides intensify the advection in the inner basin. Results can be extrapolated to other study sites with similar human interventions such as wind or wave energy converters.