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Improving current understanding of hydrodynamics and sediment dynamics in complex tidal embayments is of major importance to face future challenges derived from climate change and increasing human pressure. This work deepens the knowledge of the hydro-morphodynamics of complex creek networks that connect basins with different characteristics, identifying their morphodynamic trends and the potential impacts of channel deepening. We selected two tidal creeks which flow through salt marshes and tidal flats of the Cádiz Bay (SW Spain) in a singular network due to their double connection to the Atlantic Ocean and the inner bay. We study the interactions between tidal waves that penetrate into the creeks from these two different bodies of water, analyzing the tidal asymmetry and the morphodynamic tendencies of the system. For the analysis, we set up a hydro-morphodynamic model specifically developed for areas with very shallow and complex channels. Results show that the tidal wave penetrates within the tidal network both from the inner Bay and the open ocean with different amplitudes, phases and flow velocities. There is also an asymmetric pattern for the tidal flows caused by the deformation of the dominant astronomical tidal constituents, M2 and M4, due to the non-linear interaction of tidal currents with the irregular creek geometry and bottom topography. Tidal asymmetry promotes the progressive infilling of the area where the tidal waves meet closing the connection between the open ocean and the inner bay, such an infilling trend being accelerated by human interventions.

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Bays are semi-enclosed bodies of water connected to the open ocean that are formed by one or more basins with different hydrodynamic behaviors (Arheimer et al., 2015). The presence of multiple basins increases the complexity of these coastal systems from a hydrodynamic and management point of view. For example, basins near the open ocean are usually more exposed to waves (Zarzuelo, D'Alpaos, et al., 2019), which can control their hydrodynamics during storms. However, the hydrodynamics of inner basins may be driven only by wind, tides and/or baroclinic flows that are mainly triggered by solar radiation and stratification, since river discharges of fresh water can be usually negligible in bays, such as the bays of San Francisco

Despite relevant advances achieved in recent years, sediment transport and sedimentation problems at tidal inlets are still worldwide issues to be addressed. Furthermore, dredging strategies are carried out following traditional layouts, such as channel deepening, lasting short periods of time despite the high economic expenditures and the potential environmental impacts. This work proposes a new dredging strategy for tidal inlets and analyzes its morphodynamic evolution by means of numerical modeling. This numerical model, used to perform hydro-morphodynamic simulations, is applied to a highly altered tidal inlet (Punta Umbría inlet, Southern Spain) with a navigational capacity being continuously compromised. After calibrated and tested, the model is applied to different dredging strategies, including channel deepening, littoral drift barrier and shoal removal. Among these strategies, the shoal removal, which is a new soft-engineering strategy,

Bays are coastal environments with significant socio-economic importance, which has led to the development of human interventions in their interior that can have an important impact on the water and wave dynamics, which in turn modify their morphodynamics and water renewal capacity. In order to deepen our understanding of these impacts, numerical modeling was used in a bay in southern Spain to analyze the effect of inner harbor expansion and channel deepening, including the baroclinic and wave propagation effects, as well as variations in salinity and temperature. The results show that the deepening of the channel decreases the amplitude and speed of the tidal wave as it propagates through the bay, reducing the effects of friction and increasing the flushing time. The system evolves from convergent to a damping system that can potentially reduce the effects produced by projected sea level rise. In addition, the seasonal variability of salinity and temperature is reduced, increasing the bed shear stresses and resulting in increased turbidity that can affect the biogeochemistry of the bay. Finally, wave heights decrease along the main waterway, although the yearly-average wave energy flux is only slightly modified on the interior beaches of the bay. However, significant variations are observed during storms, which could affect the morphodynamics of these beaches.