Hydrodynamic Response of a Shallow Mesotidal Estuary to the Artificial Shifting of a Two-Jettied Inlet

Mazzolari, A., and Trigo-Teixeira, A., 2024. Hydrodynamic response of a shallow mesotidal estuary to the artificial shifting of a two-jettied inlet. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 504-508. Charlotte (North Carolina), ISSN 0749-0208. This study investigates the hydrodynamic effects of shifting the position of an inlet and navigation channel on the tidal circulation of a mesotidal estuary. The case study is represented by the Cávado estuary located on the Northern Portuguese coast, delimited from the Atlantic Ocean by an erosion-prone sand spit. At present, the shallow and migrating bed forms of the inlet do not allow safe navigation, while storm waves entering the low estuary frequently flood the waterfront promenade. This paper analyzes an alternative estuary configuration, characterized by the opening of a two-jettied inlet southward of the present position, the shortening of the navigation channel length, and the filling of the Cávado natural river mouth. The comparison of the tidal hydrodynamics between the present and new estuary configurations is carried out by means of a two-dimensional shallow water model. In the new configuration, the tidal wave has a bigger amplitude and travels less distorted along the navigation channel, as a consequence of the deeper depths, while the differences in duration between ebb and flood phases decrease with respect to the present configuration. Water volume exchanges with the Ocean show a limited variation, as the higher ebb tide fluxes calculated for the new configuration are counterbalanced by a shorter ebb phase duration.