# Observing Meteorological Tides: Fifteen Years of Statistics in the Port of La Spezia (Italy)
## 4 Discussion  
As seen in the previous paragraph, the hydrobarometric transfer factor is usually much greater within port basins than in offshore areas: A few hPa of atmospheric pressure variation can cause several cm of astronomical tide that, if in phase with the astronomical one, can generate anomalous sea level variations. The knowledge of the hydrobarometric transfer factor allows for correctly estimating expected meteorological tides in harbors and, together with the joint prediction of astronomical components from tide charts, forecasting sea level within port basins, an aspect of fundamental importance to better managing port operations. In fact, the monitoring/forecasting of sea level (and then of water depth) in coastal areas is extremely important for managing, planning, and optimizing:  
* Maritime transport and port navigation safety (e.g., to reduce the risk of accidents or to plan the refloating of a ship and minimize the risk of environmental damages and economic losses) [48; 49; 50; 51];
* Ship loading (how much to load a ship in the departure port based on the expected tide in the port of arrival) [52; 53; 54; 55];
* Dock performances and vessel moorings;
* Dimensioning of maritime works based on the maximum sea level expected;
* Dredging activities;
* The control of chemical and physical parameters of water;  
as well as preventing the risk of flooding at the mouths of rivers (civil protection purposes) by providing early warning to the population involved. For this reason, the results of this study can have important applications in coastal areas: A software tool has been developed by the research group to which the authors belong with the aim of providing useful operational support to port communities, local authorities, and decision makers; it dynamically updates the initial port bathymetric map (usually acquired through multibeam surveys and updated after changes in the harbor topography, e.g., following dredging operations) based on sea level measured or expected and, if the draught of a certain ship is known, identifies the permitted/alert/prohibited areas for that same ship at a given time. An intuitive graphical interface implements what are called \"virtual traffic lights\" by coloring the forbidden areas red, the alert zones yellow, and the allowed ones green, based on two thresholds that in their turn depend on the vessel draught. Red areas are those with depths less than the lower threshold (usually equal to the vessel's draught), green areas those with depths greater than the upper threshold (much greater than the vessel's draught); finally, yellow areas are the intermediate ones. The application continuously recalculates the \"real\" bathymetry (water depth variable over time) of a harbor using sea level data acquired in real time (by downloading them from the monitoring station via an Internet connection), measured in the past and saved in a dataset (to analyze a posteriori past events of particular importance such as the stranding of ships) or forecasted in the future by means of the hydrobarometric transfer factor and tide charts, in order to signal in advance potentially dangerous areas and avoid critical situations induced by sea level changes for a given ship. It can be very useful, e.g., for supporting a certain ship in choosing the best route to follow or the best time to enter or leave a port or the most suitable quay to moor. For example, in Figure 8, virtual traffic lights in the middle of the port of La Spezia on 30 June 2010 at 12:00 UTC are shown, when the tide gauge was measuring \(-0.54\) m. Thresholds were chosen equal to 12 and 13.5 m, e.g., for a Panamax cargo ship, whose draught is about 12 m (areas with depth less than 12 m are prohibited, those with depth greater than 13.5 m are permitted, the others are warning areas).