## 4 Discussion
The geometric stretching appeared to have a limited effect on water circulation, modulating the water exchange in the mouth (see SIMU 6 vs. SIMU 2). This reduction in the mouth width accords with [5], who has suggested that constrictions block wind-induced flushing and affect along-estuary salinity gradients. The mixing mechanism in very-shallow bays due strong winds has been illustrated by [6] in a similar domain than Fangar Bay. During these episodes pycnocline is tilted and becomes nearly vertical. In these cases, mixing is fast and largely driven by shear, and the interface becomes less defined. Numerical experiments based on our simple geometric model, including density variability, are suggested for further experiments focusing on the relationship between bathymetry variability and the evolution of the hydrographic structure. Remote winds may also produce water currents which flow against the local wind within the estuary. This behavior has been observed in Delaware or Chesapeake estuaries for low frequencies and is caused by a coastal Ekman set up due to remote wind effect [4; 37]. The remote wind effect seems not relevant due to the small scale and depth of the Fangar Bay, being the local frictional effects prevailing such as will be discussed in the next paragraph. Additionally, energetic wind events in Ebro delta (i.e., north-easterlies and north-westerlies winds) tends to affect a substantial percentage of the continental shelf being the wind spatial variability small [38]. However, the implementation of a nested numerical model using real configuration may solve the remote wind effect in Fangar Bay. Observations in Fangar Bay indicated that the water circulation was complex during calm periods: current velocities were very small and lacked a clear pattern (see Figures 5, 8 and 9), consistent with other contributions mentioned above. Momentum balance can facilitate analysis of the mechanism governing water circulation [38]. In very shallow domains, the bottom frictional term (\(\tau^{\text{B}}\)) in depth-averaged momentum balance equations (i.e., \(\tau^{\text{B}}/\rho H\)) may prove relevant (i.e., \(\text{H}^{-1}\) relation), indicating a substantial effect on water fluctuations. This means that local bathymetric disturbances may have a relevant role in modifying the flow. Similar findings were attained by [PERSON] et al. [9], observing how a complex, non-linear residual force leads to a stratified estuary in the case of Mobile (USA). These studies reveal that during calm or weak wind periods, being shallow and narrow areas, estuarine circulation is weak and occurs at the expense of frictional parameters, rendering a stable circulation pattern non-existent. Although water circulation in the inner Fangar Bay proved chaotic and complex, periods of wind intensity of up 9 m-s\({}^{-1}\) substantially modified water circulation within the Bay's basin. The effects of the energetic NW winds (up-bay wind) on the hydrodynamics could be clearly observed in the results. The observational results in Fangar Bay revealed that mixing occurred when the wind was equal to 10 m-s\({}^{-1}\) (Beaufort scale 5), as seen in Figure 10c,d. [PERSON] et al. [39] similarly observed that only a constant high-magnitude wind was capable of flushing the Indian River Lagoon, while [PERSON] et al. [35] noted that in Mobile Bay, winds of 10-15 m-s\({}^{-1}\) could break the strong stratification and completely mix the water column until strong river discharges re-stratified the water again. Furthermore, [PERSON] [5] obtained data from two estuaries on Cape Cod (USA) where weak circulation during onshore winds was altered by wind force, inhibiting circulation in the estuary. Mixing was even observed during summer, when temperatures reached 28 \({}^{\circ}\)C (Figure 8f). Persistent warm conditions in Fangar Bay have been associated with increases in mussel mortality and oyster growth [40]. The fact that the NW winds cool the water, as observed in the Figures 8 and 9, in a relatively short time aid aquaculture activity.